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Leaky Electolytics in Philips 'scope
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Cursitor Doom
Mar 22, 2015, 10:20:10 AM3/22/15
to
Hi all,
I've just got around to troubleshooting this old Philips scope that was
given to me by some chap who was moving abroad. It's the PM3264 model and
appears to be a well-constructed four channel job. It's blowing the 2A
fuses that are contained in the fuse-holder at the rear of the
instrument, so something's gone low-res. I can't see any obvious signs of
anything having burned-out on any of the boards, but a lot of the
electroytics - most of them in fact, are testing as leaky in-circuit
according to my ESR meter and before I go any further I was wondering if
that fact alone could account for the blowing fuses?
Thanks,
cd.
I've just got around to troubleshooting this old Philips scope that was
given to me by some chap who was moving abroad. It's the PM3264 model and
appears to be a well-constructed four channel job. It's blowing the 2A
fuses that are contained in the fuse-holder at the rear of the
instrument, so something's gone low-res. I can't see any obvious signs of
anything having burned-out on any of the boards, but a lot of the
electroytics - most of them in fact, are testing as leaky in-circuit
according to my ESR meter and before I go any further I was wondering if
that fact alone could account for the blowing fuses?
Thanks,
cd.
Cursitor Doom
Mar 22, 2015, 10:31:50 AM3/22/15
to
On Sun, 22 Mar 2015 14:19:14 +0000, Cursitor Doom wrote:
I should have said the caps I refer to are the small, low voltage ones on
the signal boards, NOT the large ones in the PSU section.
I should have said the caps I refer to are the small, low voltage ones on
the signal boards, NOT the large ones in the PSU section.
N_Cook
Mar 22, 2015, 10:46:09 AM3/22/15
to
slowish soft blown?
How do the fuses fare if you try running off a variac at say 60 percent
mains?
Cursitor Doom
Mar 22, 2015, 11:02:42 AM3/22/15
to
fuse blew at only about 80V!
I've got one of the PSU covers off now and have identified a suspect
component. It's some sort of capacitor with the following markings:
250V, 0.22uF@X fo=3,00Mhz
and it has a fine web of cracks over its encapsulation. I had one of
these go short-circuit once before in a microscope power supply and that
was the cause of it blowing fuses too.
I don't understand the markings on the component, though. IIRC, "fo"
refers to the self-resonant frequency and I don't see what purpose there
would be in that at 50hz mains where it's located in that part of the
device pre-PSU!
Gareth Magennis
Mar 22, 2015, 12:36:08 PM3/22/15
to
"Cursitor Doom" wrote in message news:memj12$tl2$1...@dont-email.me...
circuitry around it is discharging it whilst the meter is trying to measure
it, and thus it can't be measured whilst in circuit, and it might be
perfectly OK?
Gareth.
Cursitor Doom
Mar 22, 2015, 12:47:18 PM3/22/15
to
unfamiliar with, first time I've used it, and the readout messages aren't
terribly grammatical. But I've moved on now and narrowed the fault down
to the pre-PSU area.
There's one of those aluminium cased mains filters next inline down from
the 2A fuse compartment and it's measuring only 1ohm across it! However,
measuring the resistance looking into the scope circuitry after
disconnecting this results in an open circuit reading, so replacing the
filter alone will not fix the problem. Probably the filter just blew and
took out something further down the line. More investigation required....
Reinhard Zwirner
Mar 22, 2015, 1:17:32 PM3/22/15
to
Cursitor Doom schrieb:
[...]
here:
<http://www.okaya.com/products/noise-surge/capacitors/capacitors-faq/>
HTH
Reinhard
[...]
> 250V, 0.22uF@X fo=3,00Mhz
>
> and it has a fine web of cracks over its encapsulation. I had one of
> these go short-circuit once before in a microscope power supply and that
> was the cause of it blowing fuses too.
> I don't understand the markings on the component, though. IIRC, "fo"
> refers to the self-resonant frequency and I don't see what purpose there
> would be in that at 50hz mains where it's located in that part of the
> device pre-PSU!
Search for "X capacitor", e. g.
>
> and it has a fine web of cracks over its encapsulation. I had one of
> these go short-circuit once before in a microscope power supply and that
> was the cause of it blowing fuses too.
> I don't understand the markings on the component, though. IIRC, "fo"
> refers to the self-resonant frequency and I don't see what purpose there
> would be in that at 50hz mains where it's located in that part of the
> device pre-PSU!
here:
<http://www.okaya.com/products/noise-surge/capacitors/capacitors-faq/>
HTH
Reinhard
mike
Mar 22, 2015, 3:28:08 PM3/22/15
to
On 3/22/2015 8:01 AM, Cursitor Doom wrote:
> On Sun, 22 Mar 2015 14:46:03 +0000, N_Cook wrote:
>
>> On 22/03/2015 14:30, Cursitor Doom wrote:
>>> On Sun, 22 Mar 2015 14:19:14 +0000, Cursitor Doom wrote:
>>>
>>> I should have said the caps I refer to are the small, low voltage ones
>>> on the signal boards, NOT the large ones in the PSU section.
>>>
>>>
>> Unlikely caps problem. Hard (ie black stained)quickly blown fuses or
>> slowish soft blown?
>> How do the fuses fare if you try running off a variac at say 60 percent
>> mains?
>
> T-rated fuses. In fact I was running off a Variac when the replacement
> fuse blew at only about 80V!
Simple experiment.
> On Sun, 22 Mar 2015 14:46:03 +0000, N_Cook wrote:
>
>> On 22/03/2015 14:30, Cursitor Doom wrote:
>>> On Sun, 22 Mar 2015 14:19:14 +0000, Cursitor Doom wrote:
>>>
>>> I should have said the caps I refer to are the small, low voltage ones
>>> on the signal boards, NOT the large ones in the PSU section.
>>>
>>>
>> Unlikely caps problem. Hard (ie black stained)quickly blown fuses or
>> slowish soft blown?
>> How do the fuses fare if you try running off a variac at say 60 percent
>> mains?
>
> T-rated fuses. In fact I was running off a Variac when the replacement
> fuse blew at only about 80V!
80V x 2A = 160W.
run it at 75V and see what melts.
> I've got one of the PSU covers off now and have identified a suspect
> component. It's some sort of capacitor with the following markings:
>
> 250V, 0.22uF@X fo=3,00Mhz
>
> and it has a fine web of cracks over its encapsulation. I had one of
> these go short-circuit once before in a microscope power supply and that
> was the cause of it blowing fuses too.
Ralph Mowery
Mar 22, 2015, 6:11:07 PM3/22/15
to
"mike" <ham...@netzero.net> wrote in message
news:men52i$925$1...@dont-email.me...
>>> T-rated fuses. In fact I was running off a Variac when the replacement
>> fuse blew at only about 80V!
>
> Simple experiment.
> 80V x 2A = 160W.
> run it at 75V and see what melts.
>
When fuses are blowing, that is not a good idea. You often melt the
>> fuse blew at only about 80V!
>
> Simple experiment.
> 80V x 2A = 160W.
> run it at 75V and see what melts.
>
transformer or something else in adition to what blows.
Fuses are often rated at somewhat above the normal current draw. With a
very bad overload , they will blow quickly enough, but at just a slight
overload, they will not blow and often the transformer or other components
will also overheat and go bad.
For simple circuits like lighting circuits or where there is lots of big
heavy duty components, I have used a light bulb in place of a fuse. Just
sort of use a bulb that has a low wattage compaired to the normal current
draw.
Cursitor Doom
Mar 22, 2015, 6:46:22 PM3/22/15
to
relevance of the "fo=3Mhz" parameter is. Neither does the Wiki page on
the subject!
mike
Mar 22, 2015, 7:43:47 PM3/22/15
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Only takes a couple of watts to make something warm enough to detect
by touch.
Had a laptop I couldn't fix because the power supply wouldn't stay up.
had to put a DC supply downstream of the inductors and stuffed
an amp into the board. Took a millivoltmeter to trace the short to a
SMT cap under a heat sink. Was really shorted, didn't get warm at all.
Cursitor Doom
Mar 22, 2015, 8:18:53 PM3/22/15
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On Sun, 22 Mar 2015 16:43:12 -0700, mike wrote:
> Had a laptop I couldn't fix because the power supply wouldn't stay up.
> had to put a DC supply downstream of the inductors and stuffed an amp
> into the board. Took a millivoltmeter to trace the short to a SMT cap
> under a heat sink. Was really shorted, didn't get warm at all.
Interesting point there I'd not considered before: if something's
> Had a laptop I couldn't fix because the power supply wouldn't stay up.
> had to put a DC supply downstream of the inductors and stuffed an amp
> into the board. Took a millivoltmeter to trace the short to a SMT cap
> under a heat sink. Was really shorted, didn't get warm at all.
*completely* shorted-out, then it won't get warm!
Phil Allison
Mar 22, 2015, 8:55:30 PM3/22/15
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Cursitor Doom wrote:
>
> Interesting, but it still doesn't answer what the
> relevance of the "fo=3Mhz" parameter is.
** fo is the *series* resonant frequency of the cap.
>
> Interesting, but it still doesn't answer what the
> relevance of the "fo=3Mhz" parameter is.
Such caps across the AC supply act as an EMI filter so their high frequency characteristics are important.
Above 3MHz, the impedance of that cap will begin rising and its effectiveness lost. A lower value cap will have a higher resonant frequency.
Allow about 15nH inductance and you will easily see how he game works.
... Phil
mike
Mar 22, 2015, 8:55:43 PM3/22/15
to
because the isolation inductors in the path were getting
too hot for comfort.
That's one of the problems fixing the old Tektronix scopes.
Those tantalum caps are REALLY shorted. Of course, the one
that fails most often requires removing the backplane just to get
at something to test.
Arfa Daily
Mar 22, 2015, 9:14:39 PM3/22/15
to
"Cursitor Doom" <cu...@notformail.com> wrote in message
news:memrl1$tl2$4...@dont-email.me...
there is a cap directly between line and neutral within the filter section,
and it is almost certainly this that has failed if you read one ohm across
those two legs. The power supply itself is a switch mode type, so downstream
of the filter - "looking into the scope circuitry" as you say - an open
circuit or thereabouts is exactly what you should expect to see ...
I would suggest that you do as someone else said, and apply some power, via
a variac, directly to the power input after the filter, and with the filter
disconnected.
Arfa
John-Del
Mar 23, 2015, 7:33:22 AM3/23/15
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On Sunday, March 22, 2015 at 12:47:18 PM UTC-4, Cursitor Doom wrote:
> There's one of those aluminium cased mains filters next inline down from
> the 2A fuse compartment and it's measuring only 1ohm across it! However,
> measuring the resistance looking into the scope circuitry after
> disconnecting this results in an open circuit reading, so replacing the
> filter alone will not fix the problem. Probably the filter just blew and
> took out something further down the line. More investigation required....
Taking a resistance measurement into a circuit can lead to abnormally low or high resistance readings depending on the dmm used, and sometimes you can recheck them and get totally different readings. I would try feeding fused AC into it past the disconnected filter and see what happens.
> There's one of those aluminium cased mains filters next inline down from
> the 2A fuse compartment and it's measuring only 1ohm across it! However,
> measuring the resistance looking into the scope circuitry after
> disconnecting this results in an open circuit reading, so replacing the
> filter alone will not fix the problem. Probably the filter just blew and
> took out something further down the line. More investigation required....
Cursitor Doom
Mar 23, 2015, 7:58:19 AM3/23/15
to
have any schematics as yet; I've tried searching and the only hit I got
was some French forum where you have to join to get anything. I'm
considering it...
> I would suggest that you do as someone else said, and apply some power,
> via a variac, directly to the power input after the filter, and with the
> filter disconnected.
it a go and report back later.
Cursitor Doom
Mar 23, 2015, 8:02:09 AM3/23/15
to
purpose exactly? To prevent noise on the mains from other appliances
getting into the scope, or to prevent noise from the scope getting into
the mains?
Cursitor Doom
Mar 23, 2015, 9:48:00 AM3/23/15
to
On Mon, 23 Mar 2015 01:14:32 +0000, Arfa Daily wrote:
decent DVM.
> I would suggest that you do as someone else said, and apply some power,
> via a variac, directly to the power input after the filter, and with the
> filter disconnected.
to 100V on the variac and no sign of life from the scope yet (230V main
here). Unfortunately the PSU section is sandwiched in the middle of other
boards, so probing for voltages within it is not possible without removal
(which looks a right PITA). I'll have to have a good think about how to
proceed further.
Mike Tomlinson
Mar 23, 2015, 12:20:19 PM3/23/15
to
En el artículo <memlgt$tl2$3...@dont-email.me>, Cursitor Doom
<cu...@notformail.com> escribió:
>I've got one of the PSU covers off now and have identified a suspect
>component. It's some sort of capacitor with the following markings:
>
>250V, 0.22uF@X fo=3,00Mhz
>
>and it has a fine web of cracks over its encapsulation. I had one of
>these go short-circuit once before in a microscope power supply and that
>was the cause of it blowing fuses too.
>I don't understand the markings on the component, though. IIRC, "fo"
>refers to the self-resonant frequency and I don't see what purpose there
>would be in that at 50hz mains where it's located in that part of the
>device pre-PSU!
It's a class X mains filter capacitor. The appearance you describe
(mesh of cracks) is common when they fail. Usually they go with a bang
and a lot of smoke.
It will be ok to test the oscilloscope with out it in circuit to see if
it is the cause of the blowing fuses, but you should replace it
eventually. Note again this is class X, and should only be replaced
with another class X.
--
:: je suis Charlie :: yo soy Charlie :: ik ben Charlie ::
<cu...@notformail.com> escribió:
>I've got one of the PSU covers off now and have identified a suspect
>component. It's some sort of capacitor with the following markings:
>
>250V, 0.22uF@X fo=3,00Mhz
>
>and it has a fine web of cracks over its encapsulation. I had one of
>these go short-circuit once before in a microscope power supply and that
>was the cause of it blowing fuses too.
>I don't understand the markings on the component, though. IIRC, "fo"
>refers to the self-resonant frequency and I don't see what purpose there
>would be in that at 50hz mains where it's located in that part of the
>device pre-PSU!
(mesh of cracks) is common when they fail. Usually they go with a bang
and a lot of smoke.
It will be ok to test the oscilloscope with out it in circuit to see if
it is the cause of the blowing fuses, but you should replace it
eventually. Note again this is class X, and should only be replaced
with another class X.
--
:: je suis Charlie :: yo soy Charlie :: ik ben Charlie ::
JC
Mar 23, 2015, 1:39:12 PM3/23/15
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On 3/23/2015 9:47 AM, Cursitor Doom wrote:
> Have now done this and it isn't blowing fuses any more. However, I'm up
> to 100V on the variac and no sign of life from the scope yet (230V main
> here). Unfortunately the PSU section is sandwiched in the middle of other
> boards, so probing for voltages within it is not possible without removal
> (which looks a right PITA). I'll have to have a good think about how to
> proceed further.
>
The power board is very easy to remove, a couple of screws and plugs and
> Have now done this and it isn't blowing fuses any more. However, I'm up
> to 100V on the variac and no sign of life from the scope yet (230V main
> here). Unfortunately the PSU section is sandwiched in the middle of other
> boards, so probing for voltages within it is not possible without removal
> (which looks a right PITA). I'll have to have a good think about how to
> proceed further.
>
it pulls out the rear of the scope. I suggest you get the service
manual. Philips power supplies all have dried out axial caps and won't
start up, you wont get anywhere without replacing them. That's usually
all you need to do, they are well built apart from that.
DaveC
Mar 23, 2015, 1:41:30 PM3/23/15
to
> Have now done this and it isn't blowing fuses any more. However, I'm up
> to 100V on the variac and no sign of life from the scope yet (230V main
> here). Unfortunately the PSU section is sandwiched in the middle of other
> boards, so probing for voltages within it is not possible without removal
> (which looks a right PITA). I'll have to have a good think about how to
> proceed further.
How is 115/230 volts mains selected? Is it in the line filter/fuse/IEC
> to 100V on the variac and no sign of life from the scope yet (230V main
> here). Unfortunately the PSU section is sandwiched in the middle of other
> boards, so probing for voltages within it is not possible without removal
> (which looks a right PITA). I'll have to have a good think about how to
> proceed further.
connector housing? Or...?
Of course when bypassing the line filter you're inserting your mains voltage
to the proper transformer taps...?
Cursitor Doom
Mar 23, 2015, 1:44:40 PM3/23/15
to
On Mon, 23 Mar 2015 10:41:27 -0700, DaveC wrote:
> How is 115/230 volts mains selected? Is it in the line filter/fuse/IEC
> connector housing? Or...?
Switch on the rear panel (yes, it's in the right pos.)
> How is 115/230 volts mains selected? Is it in the line filter/fuse/IEC
> connector housing? Or...?
> Of course when bypassing the line filter you're inserting your mains
> voltage to the proper transformer taps...?
Cursitor Doom
Mar 23, 2015, 1:54:40 PM3/23/15
to
On Mon, 23 Mar 2015 13:39:08 -0400, JC wrote:
> The power board is very easy to remove, a couple of screws and plugs and
> it pulls out the rear of the scope. I suggest you get the service
> manual. Philips power supplies all have dried out axial caps and won't
> start up, you wont get anywhere without replacing them. That's usually
> all you need to do, they are well built apart from that.
Thanks for that. I've now got it out and it's evident it's been repaired
> The power board is very easy to remove, a couple of screws and plugs and
> it pulls out the rear of the scope. I suggest you get the service
> manual. Philips power supplies all have dried out axial caps and won't
> start up, you wont get anywhere without replacing them. That's usually
> all you need to do, they are well built apart from that.
before. I'll try to post some pictures later on. Actually all the axial
electrolytics have tested fine, surprisingly. I have spotted one small,
old-style polyester cap that's cracked but aside from that, nothing
obvious apart from 'historical charring' which someone has cleaned up and
replaced a couple of diodes.
At least now I can get at it, power it up and make some voltage checks!
Does anyone know if it needs to see a load to produce an output? Being of
a certain age, I'm more of a linear psu person...
DaveC
Mar 23, 2015, 2:01:47 PM3/23/15
to
>> How is 115/230 volts mains selected? Is it in the line filter/fuse/IEC
>> connector housing? Or...?
>
> Switch on the rear panel (yes, it's in the right pos.)
>
>> Of course when bypassing the line filter you're inserting your mains
>> voltage to the proper transformer taps...?
>
> It's a SMPS!
If it's a SMPS (with presumably universal input voltage), what's the switch
>> connector housing? Or...?
>
> Switch on the rear panel (yes, it's in the right pos.)
>
>> Of course when bypassing the line filter you're inserting your mains
>> voltage to the proper transformer taps...?
>
> It's a SMPS!
for?
Arfa Daily
Mar 23, 2015, 3:47:02 PM3/23/15
to
>
> Have now done this and it isn't blowing fuses any more. However, I'm up
> to 100V on the variac and no sign of life from the scope yet (230V main
> here). Unfortunately the PSU section is sandwiched in the middle of other
> boards, so probing for voltages within it is not possible without removal
> (which looks a right PITA). I'll have to have a good think about how to
> proceed further.
are very ill behaved in that respect. If it's got a front end problem, then
it's got it at 20 volts, let alone 100. If it goes beyond 20 volts, then
it's going to do one of three things. It's either going to burst into life
when the input volts are closer to normal, or do nothing at all no matter
what you do, or not start up until it has full input volts applied straight
off. It depends on the configuration of the control IC. Usually, they have
what's called an under volts lockout (UVL) feature on them. This prevents
the control IC from trying to start the PSU if the input volts are below a
certain threshold. Sometimes, if the volts are pushed progressively beyond
the threshold value by continuing to turn up the variac, the IC will
'recover' and start. However, some ICs never recover in this scenario, and
the only way out is to take all the volts back off, and then just go for it
with full line voltage. If it were not to start by either of those methods,
then there is a fault in the control circuit.
That is not uncommon with switchers, and is usually due to either a faulty
startup resistor, or a high ESR buffer cap on the supply volts pin to the
chip.
However, if the line input filter has definitely failed - which it sounds
like is the case - then there is unlikely to be any further problems
downstream of that filter, and I would just go ahead, bite the bullet, and
whack the volts up.
I didn't have any trouble finding the schematic online, but if you are
having trouble, mail me off-group at the address used to post this, and I'll
send it on to you.
Arfa
Arfa Daily
Mar 23, 2015, 3:59:00 PM3/23/15
to
"DaveC" <inv...@invalid.net> wrote in message
news:0001HW.D135A318...@news.eternal-september.org...
Arfa
DaveC
Mar 23, 2015, 4:40:50 PM3/23/15
to
>> If it's a SMPS (with presumably universal input voltage), what's the
>> switch
>> for?
> It's not 'universal' as many older switchers weren't.
>
> Arfa
And so I repeat (to Cursitor): when you are bypassing the input filter be
>> switch
>> for?
> It's not 'universal' as many older switchers weren't.
>
> Arfa
sure your mains voltage is being applied to the proper input to the SMPS.
Dave
Cursitor Doom
Mar 23, 2015, 5:22:34 PM3/23/15
to
On Mon, 23 Mar 2015 19:46:56 +0000, Arfa Daily wrote:
> However, if the line input filter has definitely failed - which it
> sounds like is the case - then there is unlikely to be any further
> problems downstream of that filter, and I would just go ahead, bite the
> bullet, and whack the volts up.
Thanks, Arfa. Well I snipped the filter completely out of circuit and
> However, if the line input filter has definitely failed - which it
> sounds like is the case - then there is unlikely to be any further
> problems downstream of that filter, and I would just go ahead, bite the
> bullet, and whack the volts up.
checked it and it clocked at 0.9ohms so for sure something fused inside.
It's rated at 250V/1A and I just happen to have a new spare one which is
unusually fortunate. Now the psu board is out of circuit I feel a bit
happier about zapping it with full volts. I'll give it a whirl in the
morning as it's getting late here now.
cheers, cd.
Cursitor Doom
Mar 23, 2015, 7:10:08 PM3/23/15
to
On Mon, 23 Mar 2015 13:40:47 -0700, DaveC wrote:
> And so I repeat (to Cursitor): when you are bypassing the input filter
> be sure your mains voltage is being applied to the proper input to the
> SMPS.
>
> Dave
That makes a lot more sense now, Dave, thanks.
> And so I repeat (to Cursitor): when you are bypassing the input filter
> be sure your mains voltage is being applied to the proper input to the
> SMPS.
>
> Dave
Arfa Daily
Mar 23, 2015, 9:30:54 PM3/23/15
to
news:0001HW.D135C85F...@news.eternal-september.org...
If you look at the schematic, it only has one two-wire input for the mains
to be applied to. Whether that input is expecting 110 v or 230 v is a
function of which way the voltage select switch in the bridge circuit is set
Arfa
to be applied to. Whether that input is expecting 110 v or 230 v is a
function of which way the voltage select switch in the bridge circuit is set
Arfa
DaveC
Mar 23, 2015, 11:47:23 PM3/23/15
to
> If you look at the schematic,
Are these available on-line?
> it only has one two-wire input for the mains
> to be applied to. Whether that input is expecting 110 v or 230 v is a
> function of which way the voltage select switch in the bridge circuit is set
> Arfa
to the PS, then it *is* universal input.
If there's a switch, then I can't imagine only 2 wires input to the PS (the
filter/switch can't drop half the mains without a transformer)...?
Admittedly confused,
Dave
Gareth Magennis
Mar 24, 2015, 4:11:40 AM3/24/15
to
"DaveC" wrote in message
news:0001HW.D1362C59...@news.eternal-september.org...
switched/connected to rectify the mains.
For 110v operation, they incorporate a voltage doubler, 240v not so.
Gareth.
Cursitor Doom
Mar 24, 2015, 5:08:39 AM3/24/15
to
On Tue, 24 Mar 2015 08:11:30 +0000, Gareth Magennis wrote:
> "DaveC" wrote in message
> news:0001HW.D1362C59...@news.eternal-september.org...
>
>> If you look at the schematic,
>
> Are these available on-line?
>
>> it only has one two-wire input for the mains to be applied to. Whether
>> that input is expecting 110 v or 230 v is a function of which way the
>> voltage select switch in the bridge circuit is set Arfa
>
> If the PS can accept 115 or 230 and if there's only 2 wires for mains
> input to the PS, then it *is* universal input.
>
> If there's a switch, then I can't imagine only 2 wires input to the PS
> (the filter/switch can't drop half the mains without a transformer)...?
>
> Admittedly confused,
> Dave
There are *two* mains input sockets on the board - in addition to the
> "DaveC" wrote in message
> news:0001HW.D1362C59...@news.eternal-september.org...
>
>> If you look at the schematic,
>
> Are these available on-line?
>
>> it only has one two-wire input for the mains to be applied to. Whether
>> that input is expecting 110 v or 230 v is a function of which way the
>> voltage select switch in the bridge circuit is set Arfa
>
> If the PS can accept 115 or 230 and if there's only 2 wires for mains
> input to the PS, then it *is* universal input.
>
> If there's a switch, then I can't imagine only 2 wires input to the PS
> (the filter/switch can't drop half the mains without a transformer)...?
>
> Admittedly confused,
> Dave
rear panel switch. I plan to post a pic of the board shortly, then all
will become clear hopefully.
Phil Allison
Mar 24, 2015, 6:01:39 AM3/24/15
to
Cursitor Doom wrote:
... Phil
Phil Allison wrote:
>
> >
> >> Interesting, but it still doesn't answer what the relevance of the
> >> "fo=3Mhz" parameter is.
> >
> >
> > ** fo is the *series* resonant frequency of the cap.
> >
> > Such caps across the AC supply act as an EMI filter so their high
> > frequency characteristics are important.
> >
> > Above 3MHz, the impedance of that cap will begin rising and its
> > effectiveness lost. A lower value cap will have a higher resonant
> > frequency.
> >
> > Allow about 15nH inductance and you will easily see how he game works.
> >
>
>
> >
> >> Interesting, but it still doesn't answer what the relevance of the
> >> "fo=3Mhz" parameter is.
> >
> >
> > ** fo is the *series* resonant frequency of the cap.
> >
> > Such caps across the AC supply act as an EMI filter so their high
> > frequency characteristics are important.
> >
> > Above 3MHz, the impedance of that cap will begin rising and its
> > effectiveness lost. A lower value cap will have a higher resonant
> > frequency.
> >
> > Allow about 15nH inductance and you will easily see how he game works.
> >
>
> Thanks for that. I'll try simulating it later. And this is for what
> purpose exactly? To prevent noise on the mains from other appliances
> getting into the scope, or to prevent noise from the scope getting into
> the mains?
** Seeing as the unit has a SMPS - it's the latter.
> purpose exactly? To prevent noise on the mains from other appliances
> getting into the scope, or to prevent noise from the scope getting into
> the mains?
... Phil
Cursitor Doom
Mar 24, 2015, 6:51:58 AM3/24/15
to
Changed the subject to reflect the progress made over the last day or
two. I've now uploaded pics of the PSU board. You can see where it's been
repaired before and evidence of a previous burn-out. It looks a little
tired in places overall. Check it out:
https://www.flickr.com/photos/128859641@N02/
Arfa Daily
Mar 24, 2015, 12:11:55 PM3/24/15
to
news:0001HW.D1362C59...@news.eternal-september.org...
that it applies to designs that by whatever method - usually by having a PFC
front end in better designs - can work with any input voltage from anywhere
in the world without requiring any kind of user intervention.
>
> If there's a switch, then I can't imagine only 2 wires input to the PS
> (the
> filter/switch can't drop half the mains without a transformer)...?
>
> Admittedly confused,
You are misunderstanding how this front end topology works. The high mains
voltage in Europe compared to the low voltage in the U.S. - or even lower in
Japan - is not reduced by the input circuitry. Rather, those low voltages
are doubled to bring the resulting output from the bridge up to the same
ballpark as is achieved when European mains is applied. I would suggest that
you have a read of the second heading down - "Voltage Doubler and Tripler"
in this Wiki
http://en.wikipedia.org/wiki/Voltage_multiplier
which details exactly how the front end of SMPSs like the one in the Philips
scope, achieve this end with the aid of a single pole voltage select switch
Arfa
> Dave
>
>
>> If you look at the schematic,
>
> Are these available on-line?
>
>> it only has one two-wire input for the mains
>> to be applied to. Whether that input is expecting 110 v or 230 v is a
>> function of which way the voltage select switch in the bridge circuit is
>> set
>> Arfa
>
> If the PS can accept 115 or 230 and if there's only 2 wires for mains
> input
> to the PS, then it *is* universal input.
No it isn't. The term "universal" when applied to a SMPS is very specific in
>
> Are these available on-line?
>
>> it only has one two-wire input for the mains
>> to be applied to. Whether that input is expecting 110 v or 230 v is a
>> function of which way the voltage select switch in the bridge circuit is
>> set
>> Arfa
>
> If the PS can accept 115 or 230 and if there's only 2 wires for mains
> input
> to the PS, then it *is* universal input.
that it applies to designs that by whatever method - usually by having a PFC
front end in better designs - can work with any input voltage from anywhere
in the world without requiring any kind of user intervention.
>
> If there's a switch, then I can't imagine only 2 wires input to the PS
> (the
> filter/switch can't drop half the mains without a transformer)...?
>
> Admittedly confused,
voltage in Europe compared to the low voltage in the U.S. - or even lower in
Japan - is not reduced by the input circuitry. Rather, those low voltages
are doubled to bring the resulting output from the bridge up to the same
ballpark as is achieved when European mains is applied. I would suggest that
you have a read of the second heading down - "Voltage Doubler and Tripler"
in this Wiki
http://en.wikipedia.org/wiki/Voltage_multiplier
which details exactly how the front end of SMPSs like the one in the Philips
scope, achieve this end with the aid of a single pole voltage select switch
Arfa
> Dave
>
>
DaveC
Mar 24, 2015, 11:15:39 PM3/24/15
to
> which details exactly how the front end of SMPSs like the one in the Philips
> scope, achieve this end with the aid of a single pole voltage select switch
>
> Arfa
Ah, so the Philips' ps has a voltage doubler at its front end controlled by
> scope, achieve this end with the aid of a single pole voltage select switch
>
> Arfa
the "mains switch". The input to the ps *proper* is the same--240--fed by
either the 240 mains directly or the 120 mains, doubled.
Thanks,
Dave
Ian Field
Mar 25, 2015, 4:43:19 PM3/25/15
to
"Ralph Mowery" <rmower...@earthlink.net> wrote in message
news:nNydndhe9vZroJLI...@earthlink.com...
>
> "mike" <ham...@netzero.net> wrote in message
> news:men52i$925$1...@dont-email.me...
>>>> T-rated fuses. In fact I was running off a Variac when the replacement
>>> fuse blew at only about 80V!
>>
>> Simple experiment.
>> 80V x 2A = 160W.
>> run it at 75V and see what melts.
>>
> When fuses are blowing, that is not a good idea. You often melt the
> transformer or something else in adition to what blows.
>
> Fuses are often rated at somewhat above the normal current draw. With a
> very bad overload , they will blow quickly enough, but at just a slight
> overload, they will not blow and often the transformer or other components
> will also overheat and go bad.
Its also a pretty good way to fry a variac - they're not as robust as
regular fixed mains transformers.
Ian Field
Mar 25, 2015, 4:47:40 PM3/25/15
to
news:menm3p$4rf$6...@dont-email.me...
> On Sun, 22 Mar 2015 16:43:12 -0700, mike wrote:
>
>> Had a laptop I couldn't fix because the power supply wouldn't stay up.
>> had to put a DC supply downstream of the inductors and stuffed an amp
>> into the board. Took a millivoltmeter to trace the short to a SMT cap
>> under a heat sink. Was really shorted, didn't get warm at all.
>
> Interesting point there I'd not considered before: if something's
> *completely* shorted-out, then it won't get warm!
An old service engineer's trick is to bridge the fuse with a 60W light bulb,
then you can check voltages into the mains front end and get some idea
what's holding things up.
Its worth remembering the lightbulb filament has a PTC characteristic, so
there will be some inrush surge - calculating the value for an equivalent
power resistor would avoid that.
> On Sun, 22 Mar 2015 16:43:12 -0700, mike wrote:
>
>> Had a laptop I couldn't fix because the power supply wouldn't stay up.
>> had to put a DC supply downstream of the inductors and stuffed an amp
>> into the board. Took a millivoltmeter to trace the short to a SMT cap
>> under a heat sink. Was really shorted, didn't get warm at all.
>
> Interesting point there I'd not considered before: if something's
> *completely* shorted-out, then it won't get warm!
An old service engineer's trick is to bridge the fuse with a 60W light bulb,
then you can check voltages into the mains front end and get some idea
what's holding things up.
Its worth remembering the lightbulb filament has a PTC characteristic, so
there will be some inrush surge - calculating the value for an equivalent
power resistor would avoid that.
Gareth Magennis
Mar 25, 2015, 5:44:47 PM3/25/15
to
"Ian Field" wrote in message news:g5FQw.1544614$bY7.1...@fx02.am4...
I would never now fire up a Variac without a lightbulb in series to let me
know what is going on.
(Mine now has a rather crusty section of windings that fortunately still
works after 10 years or so)
Gareth.
Ian Field
Mar 25, 2015, 5:48:07 PM3/25/15
to
"Gareth Magennis" <sound....@btconnect.com> wrote in message
news:h%FQw.1282302$ci4.1...@fx39.am4...
>
>
> "Ian Field" wrote in message news:g5FQw.1544614$bY7.1...@fx02.am4...
>
>
> "Ralph Mowery" <rmower...@earthlink.net> wrote in message
> news:nNydndhe9vZroJLI...@earthlink.com...
>>
>> "mike" <ham...@netzero.net> wrote in message
>> news:men52i$925$1...@dont-email.me...
>>>>> T-rated fuses. In fact I was running off a Variac when the replacement
>>>> fuse blew at only about 80V!
>>>
>>> Simple experiment.
>>> 80V x 2A = 160W.
>>> run it at 75V and see what melts.
>>>
>> When fuses are blowing, that is not a good idea. You often melt the
>> transformer or something else in adition to what blows.
>>
>> Fuses are often rated at somewhat above the normal current draw. With a
>> very bad overload , they will blow quickly enough, but at just a slight
>> overload, they will not blow and often the transformer or other
>> components will also overheat and go bad.
>
> Its also a pretty good way to fry a variac - they're not as robust as
> regular fixed mains transformers.
>
>
>
> I learnt that on almost the first time I used mine.
Its probably because they're very large for a given rating - easy to
>
> "Ian Field" wrote in message news:g5FQw.1544614$bY7.1...@fx02.am4...
>
>
> "Ralph Mowery" <rmower...@earthlink.net> wrote in message
> news:nNydndhe9vZroJLI...@earthlink.com...
>>
>> "mike" <ham...@netzero.net> wrote in message
>> news:men52i$925$1...@dont-email.me...
>>>>> T-rated fuses. In fact I was running off a Variac when the replacement
>>>> fuse blew at only about 80V!
>>>
>>> Simple experiment.
>>> 80V x 2A = 160W.
>>> run it at 75V and see what melts.
>>>
>> When fuses are blowing, that is not a good idea. You often melt the
>> transformer or something else in adition to what blows.
>>
>> Fuses are often rated at somewhat above the normal current draw. With a
>> very bad overload , they will blow quickly enough, but at just a slight
>> overload, they will not blow and often the transformer or other
>> components will also overheat and go bad.
>
> Its also a pretty good way to fry a variac - they're not as robust as
> regular fixed mains transformers.
>
>
>
> I learnt that on almost the first time I used mine.
misjudge, and then the magic smoke comes out.
Arfa Daily
Mar 25, 2015, 9:45:18 PM3/25/15
to
news:0001HW.D1377668...@news.eternal-september.org...
That's about the long and the short of it, yes, but of course the input to
the "ps *proper* " as you call it, is DC from the bridge/ doubler, so
actually much higher than 240. Closer to 385 v DC when it is operating on UK
/ European mains
Arfa
the "ps *proper* " as you call it, is DC from the bridge/ doubler, so
actually much higher than 240. Closer to 385 v DC when it is operating on UK
/ European mains
Arfa
DaveC
Mar 26, 2015, 11:21:09 AM3/26/15
to
> That's about the long and the short of it, yes, but of course the input to
> the "ps *proper* " as you call it, is DC from the bridge/ doubler, so
> actually much higher than 240. Closer to 385 v DC when it is operating on UK
> / European mains
>
> Arfa
Input to the ps proper is either rectified (240vac) mains or rectified
> the "ps *proper* " as you call it, is DC from the bridge/ doubler, so
> actually much higher than 240. Closer to 385 v DC when it is operating on UK
> / European mains
>
> Arfa
(120vac) mains *doubled*, depending on switch position.
Dave
Ian Field
Mar 26, 2015, 3:05:19 PM3/26/15
to
news:0001HW.D13971E7...@news.eternal-september.org...
The usual scheme being the main electrolytic is split into a series pair
across the plus and minus lugs of the bridge rectifier.
For 230V operation the switch is left open - for 120V, the switch is closed
to connect the junction of the 2 electrolytics to one AC lug on the bridge,
that converts the bridge into a voltage doubling rectifier.
In text books, you often see a voltage doubler with the same layout as a
bridge rectifier, but 2 of the rectifiers are replaced by capacitors - the
original diodes of a full complement bridge don't do any harm in a doubler
even though they're not needed, but they are needed for the non-doubling
configuration and leaving them there makes for simpler switching.
across the plus and minus lugs of the bridge rectifier.
For 230V operation the switch is left open - for 120V, the switch is closed
to connect the junction of the 2 electrolytics to one AC lug on the bridge,
that converts the bridge into a voltage doubling rectifier.
In text books, you often see a voltage doubler with the same layout as a
bridge rectifier, but 2 of the rectifiers are replaced by capacitors - the
original diodes of a full complement bridge don't do any harm in a doubler
even though they're not needed, but they are needed for the non-doubling
configuration and leaving them there makes for simpler switching.
Cursitor Doom
Mar 26, 2015, 7:13:59 PM3/26/15
to
On Wed, 25 Mar 2015 21:44:43 +0000, Gareth Magennis wrote:
> I would never now fire up a Variac without a lightbulb in series to let
> me know what is going on.
Some clarification of this statement would be nice. I have an old Variac
> I would never now fire up a Variac without a lightbulb in series to let
> me know what is going on.
and don't want to see it get damaged. It has an inline fuse within it so
why isn't that in itself sufficient protection?
Cursitor Doom
Mar 26, 2015, 8:01:12 PM3/26/15
to
thought 400 min would be more suitable!
Cursitor Doom
Mar 26, 2015, 8:04:33 PM3/26/15
to
On Thu, 26 Mar 2015 19:06:07 +0000, Ian Field wrote:
> The usual scheme being the main electrolytic is split into a series pair
> across the plus and minus lugs of the bridge rectifier.
>
> For 230V operation the switch is left open - for 120V, the switch is
> closed to connect the junction of the 2 electrolytics to one AC lug on
> the bridge,
> that converts the bridge into a voltage doubling rectifier.
That's exactly what Philips have done in this particular PSU.
> The usual scheme being the main electrolytic is split into a series pair
> across the plus and minus lugs of the bridge rectifier.
>
> For 230V operation the switch is left open - for 120V, the switch is
> closed to connect the junction of the 2 electrolytics to one AC lug on
> the bridge,
> that converts the bridge into a voltage doubling rectifier.
Ron D.
Mar 26, 2015, 10:09:34 PM3/26/15
to
I need to remind people, that the wiper of the Variac (Autotransformer) needs to be fused. The windings are rated for current, so if it's 10 A at 120 V. It;s also 10 A at 10 V. A primary fuse won;t protect it.
Arfa Daily
Mar 26, 2015, 10:12:32 PM3/26/15
to
news:mf26ih$fgh$3...@dont-email.me...
Think about it ...
Arfa
Arfa
Cursitor Doom
Mar 27, 2015, 2:43:58 PM3/27/15
to
On Fri, 27 Mar 2015 02:12:20 +0000, Arfa Daily wrote:
>>
> Think about it ...
I am. But the problem at present is that I need to establish if the scope
actually works before I spend money on it. That means contriving some
temporary power supply (or *supplies* more likely) capable of generating
the wide selection of voltages that the scope itself requires. One of the
rails needs 60V and my largest PSU tops out at only 40. It's a PITA. :(
>>
> Think about it ...
I am. But the problem at present is that I need to establish if the scope
actually works before I spend money on it. That means contriving some
temporary power supply (or *supplies* more likely) capable of generating
the wide selection of voltages that the scope itself requires. One of the
rails needs 60V and my largest PSU tops out at only 40. It's a PITA. :(
Cursitor Doom
Mar 27, 2015, 2:46:59 PM3/27/15
to
has two fuses: one in the plug as usual and another in the body of the
variac. A curious looking thing with a tight, curly filament wound round
a tiny former and a rating of 3.15A.
Ian Field
Mar 27, 2015, 3:15:58 PM3/27/15
to
news:mf23q1$fgh$1...@dont-email.me...
You probably want the fastest rated fuse you can get away with for a variac.
Ian Field
Mar 27, 2015, 3:22:46 PM3/27/15
to
news:mf26ih$fgh$3...@dont-email.me...
In UK equipment (with no doubling) the electrolytic is usually at least
385V - frequently 400V.
In doubling types, the capacitors are usually 200V each.
The ones with PFC front end don't have a reservoir after the bridge - that
comes after the PFC transistor, the most common voltage rating I've seen is
450V.
385V - frequently 400V.
In doubling types, the capacitors are usually 200V each.
The ones with PFC front end don't have a reservoir after the bridge - that
comes after the PFC transistor, the most common voltage rating I've seen is
450V.
Cursitor Doom
Mar 27, 2015, 4:58:05 PM3/27/15
to
On Fri, 27 Mar 2015 19:23:39 +0000, Ian Field wrote:
> In UK equipment (with no doubling) the electrolytic is usually at least
> 385V - frequently 400V.
>
> In doubling types, the capacitors are usually 200V each.
>
> The ones with PFC front end don't have a reservoir after the bridge -
> that comes after the PFC transistor, the most common voltage rating I've
> seen is 450V.
Well, 230VAC RMS comes to 325V P-P., so Philips are pushing their luck
> In UK equipment (with no doubling) the electrolytic is usually at least
> 385V - frequently 400V.
>
> In doubling types, the capacitors are usually 200V each.
>
> The ones with PFC front end don't have a reservoir after the bridge -
> that comes after the PFC transistor, the most common voltage rating I've
> seen is 450V.
with the 350V ones they use in this scope. Especially since there will be
surges above this nominal level and general power station fluctuations
around 230V RMS anyway. The standard caps' voltage rating leaves precious
little allowance for these expected variations.
Ian Field
Mar 27, 2015, 5:30:33 PM3/27/15
to
news:mf4g77$sp1$3...@dont-email.me...
When PC PSUs were part of my bread & butter work, I often found they'd used
150V MOVs to protect each of the series 200V electrolytics. Once or twice I
encountered PSUs that had suffered a cascade failure, started by one of the
under-rated MOVs breaking down.
Maybe I saw a dozen or so that blew up - there must be thousands out there
that didn't.
150V MOVs to protect each of the series 200V electrolytics. Once or twice I
encountered PSUs that had suffered a cascade failure, started by one of the
under-rated MOVs breaking down.
Maybe I saw a dozen or so that blew up - there must be thousands out there
that didn't.
Arfa Daily
Mar 27, 2015, 9:29:06 PM3/27/15
to
news:mf4g77$sp1$3...@dont-email.me...
You are not thinking about it right, though. With the PSU set to accept a
230 volt input. the two electros are in series, so the 350v rating of them
stacks up to 700 volts across the pair - more than adequate to handle peak
rectified mains plus any 'over-voltages'. You will also note that there is a
resistor across each cap - R1801 and 1802. These serve the primary purpose
of voltage sharing to make sure that the voltage across each of the two caps
is substantially the same, and the secondary purpose of discharging the caps
safely when power is turned off.
As to trying to replace the voltages coming off the PSU, to be honest, I
feel that you are over-thinking it all. I understand that you are not
comfortable with switchers and are trying to prove out the rest of the
circuitry as safely as you can, but with the best will in the world, you are
never going to sub the 1 kV and 1.5 kV outputs of the supply, so are never
going to be able to see anything on the screen anyway.
Based on a great deal of experience of switchers, I would venture to suggest
that you found the only problem that the power supply is going to have been
suffering when you located the short circuit filter, and the best way to
proceed now is to 'just go for it ...'
Arfa
230 volt input. the two electros are in series, so the 350v rating of them
stacks up to 700 volts across the pair - more than adequate to handle peak
rectified mains plus any 'over-voltages'. You will also note that there is a
resistor across each cap - R1801 and 1802. These serve the primary purpose
of voltage sharing to make sure that the voltage across each of the two caps
is substantially the same, and the secondary purpose of discharging the caps
safely when power is turned off.
As to trying to replace the voltages coming off the PSU, to be honest, I
feel that you are over-thinking it all. I understand that you are not
comfortable with switchers and are trying to prove out the rest of the
circuitry as safely as you can, but with the best will in the world, you are
never going to sub the 1 kV and 1.5 kV outputs of the supply, so are never
going to be able to see anything on the screen anyway.
Based on a great deal of experience of switchers, I would venture to suggest
that you found the only problem that the power supply is going to have been
suffering when you located the short circuit filter, and the best way to
proceed now is to 'just go for it ...'
Arfa
Arfa Daily
Mar 27, 2015, 9:30:44 PM3/27/15
to
news:mf48hd$sp1$2...@dont-email.me...
"T" rated fuses often have a spiral element
Arfa
Arfa
Cursitor Doom
Mar 28, 2015, 11:11:41 AM3/28/15
to
On Sat, 28 Mar 2015 01:28:57 +0000, Arfa Daily wrote:
> You are not thinking about it right, though. With the PSU set to accept
> a 230 volt input. the two electros are in series, so the 350v rating of
> them stacks up to 700 volts across the pair - more than adequate to
> handle peak rectified mains plus any 'over-voltages'. You will also note
> that there is a resistor across each cap - R1801 and 1802. These serve
> the primary purpose of voltage sharing to make sure that the voltage
> across each of the two caps is substantially the same, and the secondary
> purpose of discharging the caps safely when power is turned off.
Argh! Thanks for that, Arfa. You're right of course. I still have linear
> You are not thinking about it right, though. With the PSU set to accept
> a 230 volt input. the two electros are in series, so the 350v rating of
> them stacks up to 700 volts across the pair - more than adequate to
> handle peak rectified mains plus any 'over-voltages'. You will also note
> that there is a resistor across each cap - R1801 and 1802. These serve
> the primary purpose of voltage sharing to make sure that the voltage
> across each of the two caps is substantially the same, and the secondary
> purpose of discharging the caps safely when power is turned off.
PSU topology burned into my consiousness (large electrolyitcs in
parallel). I need to get it into my thick head that switchers use a
different approach altogether (I'm a bit slow to adapt given my advanced
age).
> As to trying to replace the voltages coming off the PSU, to be honest, I
> feel that you are over-thinking it all. I understand that you are not
> comfortable with switchers and are trying to prove out the rest of the
> circuitry as safely as you can, but with the best will in the world, you
> are never going to sub the 1 kV and 1.5 kV outputs of the supply, so are
> never going to be able to see anything on the screen anyway.
rig up my PSUs for the sub 60V stuff, tbh. But I admit it would be messy
and fiddly.
> Based on a great deal of experience of switchers, I would venture to
> suggest that you found the only problem that the power supply is going
> to have been suffering when you located the short circuit filter, and
> the best way to proceed now is to 'just go for it ...'
and no supply volts even to the PWM chip. HOWEVER, ISTR from somewhere
that these things shut down if they don't see a load, so I'll leave my
"outthinking" behind for a mo (you're not the first to say that) and
reconnect everything back in circuit and re-try.
I'll report back in due course.
Arfa Daily
Mar 28, 2015, 1:06:32 PM3/28/15
to
>
> Whilst it was out of the scope I did test it and it was dead; no chopping
> and no supply volts even to the PWM chip. HOWEVER, ISTR from somewhere
> that these things shut down if they don't see a load, so I'll leave my
> "outthinking" behind for a mo (you're not the first to say that) and
> reconnect everything back in circuit and re-try.
> I'll report back in due course.
>
>
For a start, you should never work on a switcher without having it on an
isolation transformer. Secondly, it's not easy to safely measure voltages on
the primary side of the PSU without knowing what you are going to use as a
ground reference for your meter or scope. Usually, it's the -ve side of the
bridge reccy, but always check the schematic to be sure. In the case of the
Philips, that does appear to be the right place. Bear in mind we are talking
peak rectified mains here, limited in current capacity only by the value of
any primary side fuse. Skull and crossbones stuff ... If you are not
confident measuring with two hands in this sort of environment, solder a
wire to the -ve reference point and clip your meter -ve probe to it. Then
put the hand that you would have been holding that probe with firmly in your
pocket, and don't bring it back out again until you've finished measuring
and moved away, or turned it back off. Even with it operating on an
isolation transformer, you aren't safe against hanging yourself *across*
either the mains input or the output side of the bridge. I'm sure that you
probably know all this, but better safe than sorry, and worth mentioning for
any other readers who might not be aware of the potential dangers of working
'live' on switchers ...
Supply volts for the PWM chip are on pin 1, and are supplied initially from
the rectified mains via the circuitry around V1803 and 1804. Once the supply
gets going, it is self-supplied via the diodes at V1816, 17. I don't
immediately see any active feedback from the secondary side, so I would be
surprised if it didn't at least try to start without secondary side loads,
but switchers always have the capacity to do things that you don't expect !
There is some DC feedback from the primary side via V1818 and 19, but I
would still expect it to start whilst monitoring for a control voltage
coming back from there. It looks as though it uses the level of voltage from
there to control the PWM output to set the base level of output volts and
keep them stable against secondary side load.
I have a copy of the datasheet for the chip if you would like me to send it.
It details the operation of the chip pretty well, and shows some sample
implementations of it which are pretty close to how it's being used in the
Philips, if you can get your mind to re-arrange the way they have been drawn
...
Arfa
Cursitor Doom
Mar 28, 2015, 1:59:04 PM3/28/15
to
On Sat, 28 Mar 2015 17:06:23 +0000, Arfa Daily wrote:
> Be very very - and I mean VERY - careful what you are measuring, and
> how. For a start, you should never work on a switcher without having it
> on an isolation transformer.
Indeed! I have actually ordered one (a 500W model) as I wasn't
> Be very very - and I mean VERY - careful what you are measuring, and
> how. For a start, you should never work on a switcher without having it
> on an isolation transformer.
comfortable with a mere RCD in combo with a variac between the scope and
the wall socket. In addition to the safety aspect conferred by a IT, it's
always annoying and frightening when you blow a bloody great hole in a
probe's ground shield - as I'm sure we've all done at some point - when
completing an earth loop you didn't know was there. :-)
Secondly, it's not easy to safely measure
> voltages on the primary side of the PSU without knowing what you are
> going to use as a ground reference for your meter or scope. Usually,
> it's the -ve side of the bridge reccy, but always check the schematic to
> be sure. In the case of the Philips, that does appear to be the right
> place. Bear in mind we are talking peak rectified mains here, limited in
> current capacity only by the value of any primary side fuse. Skull and
> crossbones stuff ... If you are not confident measuring with two hands
> in this sort of environment, solder a wire to the -ve reference point
> and clip your meter -ve probe to it. Then put the hand that you would
> have been holding that probe with firmly in your pocket, and don't bring
> it back out again until you've finished measuring and moved away, or
> turned it back off. Even with it operating on an isolation transformer,
> you aren't safe against hanging yourself *across* either the mains input
> or the output side of the bridge. I'm sure that you probably know all
> this, but better safe than sorry, and worth mentioning for any other
> readers who might not be aware of the potential dangers of working
> 'live' on switchers ...
only know enough to be dangerous. I have gaps in my knowledge. I need to
spend more time refreshing my knowledge of testing safety procedures. I
do recall the old 'hand behind your back' rule from a long way back,
though. And I don't fancy working two-handed with some of these DVMs you
see nowadays that claim to be CAT III or IV but are anything but when you
take them apart.
> Supply volts for the PWM chip are on pin 1, and are supplied initially
> from the rectified mains via the circuitry around V1803 and 1804. Once
> the supply gets going, it is self-supplied via the diodes at V1816, 17.
> I don't immediately see any active feedback from the secondary side, so
> I would be surprised if it didn't at least try to start without
> secondary side loads, but switchers always have the capacity to do
> things that you don't expect ! There is some DC feedback from the
> primary side via V1818 and 19, but I would still expect it to start
> whilst monitoring for a control voltage coming back from there. It looks
> as though it uses the level of voltage from there to control the PWM
> output to set the base level of output volts and keep them stable
> against secondary side load.
> I have a copy of the datasheet for the chip if you would like me to send
> it.
> It details the operation of the chip pretty well, and shows some sample
> implementations of it which are pretty close to how it's being used in
> the Philips, if you can get your mind to re-arrange the way they have
> been drawn ...
schematics that were the big problem. I'll have to check out that site
you mentioned in your email and see what's there. I've got another 2 or 3
Philips scopes to sort out when this one's done so I'm sure it would pay
off.
Arfa Daily
Mar 28, 2015, 9:48:06 PM3/28/15
to
>
> I managed to get a DS for the chip pretty quickly, it was the scope
> schematics that were the big problem. I'll have to check out that site
> you mentioned in your email and see what's there. I've got another 2 or 3
> Philips scopes to sort out when this one's done so I'm sure it would pay
> off.
eserviceinfo.com are often right at the top. I usually use the search string
manufacturer - model - free schematic download. You can of course use + and
" " operators (and others) in the string to make it more specific
elektrotanya tends to yield better results in that eserviceinfo will often
find anything in its database which matches any of your search criteria,
whereas any elektrotanya 'hit' usually takes you straight to the manual.
It's not immediately obvious how to get the manual, though. Ignore all the
big "Download" buttons that you see dotted around. These are all for
'helper' software or PDF readers. Look in the text block under the preview
pane, and you will see the word "processing" in a different colour. Small
and hard to spot. After a while - and I have known it to be several
minutes - the word will change to "get manual". If you then click on it, the
download process will start normally, and depending on your computer OS and
what antivirus blockers you have, you will probably get the "do you want to
open / save "etc dialogue box
Arfa
Cursitor Doom
Mar 29, 2015, 8:03:14 AM3/29/15
to
On Sun, 29 Mar 2015 02:47:52 +0100, Arfa Daily wrote:
> If you use Google to search for service info, elektrotanya.com and
> eserviceinfo.com are often right at the top.
[...]
> If you use Google to search for service info, elektrotanya.com and
> eserviceinfo.com are often right at the top.
Cheers, Arfa. You're a diamond.
Ian Field
Mar 29, 2015, 2:27:53 PM3/29/15
to
"Arfa Daily" <arfa....@ntlworld.com> wrote in message
news:hRIRw.491026$7E1.1...@fx31.am4...
The one I found isn't in English, so I don't know whether I'm seeing the bit
you describe.
But then I've recently stripped and re-installed my browser to sort some
problems - I had a translate button then, now I don't.
Arfa Daily
Mar 29, 2015, 8:29:48 PM3/29/15
to
"Ian Field" <gangprob...@ntlworld.com> wrote in message
news:GuXRw.192255$ID3.1...@fx01.am4...
type in :
Sony DAV-S300 free schematic download
and click search. A link to elektrotanya should be right there at the top.
Click that, and it should take you to the download page for that manual. The
page is in English, and there is a preview image for the manual in the main
pane. Immediately below that pane, is some text and on the third line it
says "This manual is downloadable free of charge ... processing"
Keep watching that word "processing", and it will eventually change to "Get
Manual", underlined. If you now mouse over that, you will get the clickable
hand. Go ahead and click it, and the manual should start to download,
subject to any restraints imposed by your OS / antivirus software. The site
has always been totally trustworthy for me - otherwise I wouldn't recommend
it - and is a very useful resource.
A bit further down the Google results list, you will see a link to the same
manual at eserviceinfo.com. If you click on that one, it will take you to a
copy on their site. Note how the page presents. It is only when the page
looks like this, that you are actually on the manual. If the page looks more
like a list made out of boxes and there seems to be a lot of writing and
model numbers, then the chances are that the manual you are looking for is
not actually there, and it is just eserviceinfo having its 'best go' at
finding you something.
Going back to our example of the Sony manual, you will see half way down
that it says "Multipart" and to the right of that "0 1 2 3 4" with the "4"
highlighted in orange. This means that the file has been saved on the site
as a rar archive of five files, and all five need to be downloaded and saved
to your machine to get the complete manual. Click on the "0" which will then
turn orange. Scroll down the page until you see :
Download >> To download the file, please, click here ! << Download
Click on the middle bit and the first part will download. Scroll back up,
and highlight "1", then back down to
Download >> To download the file, please, click here ! << Download
again and so on until all five parts have downloaded to whatever directory
you've put them in. Now just click on the first one and your Winzip or
whatever software should open to extract and recombine them into the
original pdf.
eserviceinfo also has binaries for reprogramming a lot of TV eeproms. Again
a useful resource, and one that has never caused me any problems.
Arfa
Ian Field
Mar 30, 2015, 12:50:34 PM3/30/15
to
news:ZN0Sw.1720468$i22.2...@fx07.am4...
Thanks - got it.
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