DTV decoder repair, capacitor gets too hot
Jeroni Paul
that had a swollen capacitor in the power supply. 6 months ago I
already replaced this capacitor with a low ESR high quality 105 deg
replacement but it just lasted 6 months and is swollen again.
The capacitor is EC205 1000uF 16V and is the filter for 5V output in a
switching power supply. Typical design, small transformer, rectifier
diode, first capacitor, inductor and second capacitor with TNY265 as
primary controller chip. The second capacitor remains cold and checks
fine on the ESR meter. The problem is in the first capacitor, I
replaced it again with a new 105 deg type and it works but I notice
the capacitor gets very hot in just 10 minutes. All the capacitors in
the supply check fine on the ESR meter. Tried different brands of
capacitors and the ones having the smallest ESR work better but also
get very hot.
It seems to me this receiver is too exigent on the quality and ESR of
this capacitor. Do you think this is normal and I should be looking
for a really good capacitor or should I look for another problem
elsewhere? Could I do something to reduce the stress it is put on?
The waveform on this capacitor looks like a sawtooth, rises really
fast and falls slowly until half cycle, then remains constant for the
remaining half cycle. Amplitude around 0,4Vpp to 1Vpp depending on the
capacitor used.
Plain...@yahoo.com
What brand and series of "low ESR high quality 105 deg replacement"
did you use? I would recommecd using a Panasonic FM series or
equivalent ultra-low ESR high quality ca fron Nochicon, UCC, or
Rubycon for something like this.
PlainBill
Grant
David
<Plain...@yahoo.com> wrote in message
news:gu95065uln9ebjd6n...@4ax.com...
> On Sun, 30 May 2010 04:45:45 -0700 (PDT), Jeroni Paul
> <JERON...@terra.es> wrote:
>
>>I'm repairing a DTV decoder Saivod DT2012 (chip Cheertek
>>and tuner LG)
>>that had a swollen capacitor in the power supply. 6 months
>>ago I
>>already replaced this capacitor with a low ESR high
>>quality 105 deg
>>replacement but it just lasted 6 months and is swollen
>>again.
>>
>>The capacitor is EC205 1000uF 16V and is the filter for 5V
>>output in a
>>switching power supply. Typical design, small transformer,
>>rectifier
>>diode, first capacitor, inductor and second capacitor with
>>TNY265 as
>>primary controller chip. The second capacitor remains cold
>>and checks
>>fine on the ESR meter.
Unless this is a flyback type supply, a typical forward
switching power supply design does not have a large
capacitor on the output of the rectifier. The rectifier
diodes go directly to an inductor with the main filter
capacitor connected to the output of the inductor. If it a
flyback design, you could try putting a 1 uf or so ceramic
capacitor across the larger capacitor. Using a high voltage
replacement is not a good idea since the higher the voltage
rating, the higher the ESR.
David
Grant
Since when? Quick check for 1000/25 and 1000/35 Panasonic caps
show ESR goes from .033 down to .025 for higher volt rating.
Grant.
--
http://bugs.id.au/
b
> I'm repairing a DTV decoder Saivod DT2012 (chip Cheertek and tuner LG)
> that had a swollen capacitor in the power supply. 6 months ago I
> already replaced this capacitor with a low ESR high quality 105 deg
> replacement but it just lasted 6 months and is swollen again.
>
> The capacitor is EC205 1000uF 16V and is the filter for 5V output in a
> switching power supply. Typical design, small transformer, rectifier
> diode, first capacitor, inductor and second capacitor with TNY265 as
> primary controller chip. The second capacitor remains cold and checks
> fine on the ESR meter. The problem is in the first capacitor, I
> replaced it again with a new 105 deg type and it works but I notice
> the capacitor gets very hot in just 10 minutes.
might be worth checking the current drawn, out of interest.
i've repaired dozens of these sort of boxes, many of which are the
same inside (MX Onda, AXIL, T Boston, Engel....) and using caps rated
at 25v in place of the 16v fitted usually keeps them working.
-B
Jamie
circuit. I found some that developed a leak but not enough to short and
pass some AC through from the switcher.. This can not only heat the
diode but the Cap. A simple test is to perform a thermal test on the
diode.. It should only be warm at best..
Arfa Daily
"Grant" <o...@grrr.id.au> wrote in message
news:9kv506p9te71fuuep...@4ax.com...
Agreed, and the chart on the front of my trusty Bob Parker Mk1 agrees too. I
also repair a lot of this low cost crap, and I always put a 25v cap in them.
Arfa
stra...@yahoo.com
Where I used to work they had Samsung DTV tuners that had a similar
issue. In that case we mounted the capacitor on its side to get it
farther away from the diode next to it that was the source of the
heat. You might look into the Nichicon HN series caps or possibly an
organic polymer cap. AFAIK the HN caps are the lowest (?) ESR of the
'lytics but the polymers are supposed to be even lower. Would a larger
value cap help here? What is the actual load current and what is the
frequency of the ripple?
G²
Plain...@yahoo.com
wrote:
>
>
I am always dubious about advice offered by someone who cannot
comprehend a simple text description. From the original post:
"Typical design, small transformer, rectifier diode, first capacitor,
inductor and second capacitor with TNY265 as primary controller chip.
The second capacitor remains cold and checks fine on the ESR meter."
Looking up the datasheet for the TNY265 controller I see that it does
indeed suggest the circuit description described above.
Now the question is, are you a troll, or simply uneducated?
PlainBill
Franc Zabkar
to keyboard and composed:
>Quick check for 1000/25 and 1000/35 Panasonic caps
>show ESR goes from .033 down to .025 for higher volt rating.
I just tried a thought experiment, but it failed. :-(
Let's say we have four identical capacitors, each with capacitance C,
esr R, and voltage rating V.
If we connect them as follows, we would expect the equivalent
capacitor to have a capacitance C, esr R, and voltage rating 2V.
|| ||
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o---| |---o
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- Franc Zabkar
--
Please remove one 'i' from my address when replying by email.
Franc Zabkar
>The waveform on this capacitor looks like a sawtooth, rises really
>fast and falls slowly until half cycle, then remains constant for the
>remaining half cycle. Amplitude around 0,4Vpp to 1Vpp depending on the
>capacitor used.
The current in an ideal capacitor is given by ...
I = C x dV/dt
Can you use this to estimate the current draw?
Cydrome Leader
> On Mon, 31 May 2010 10:12:44 +1000, Grant <o...@grrr.id.au> put finger
> to keyboard and composed:
>
>>Quick check for 1000/25 and 1000/35 Panasonic caps
>>show ESR goes from .033 down to .025 for higher volt rating.
>
> I just tried a thought experiment, but it failed. :-(
>
> Let's say we have four identical capacitors, each with capacitance C,
> esr R, and voltage rating V.
>
> If we connect them as follows, we would expect the equivalent
> capacitor to have a capacitance C, esr R, and voltage rating 2V.
>
> || ||
> |---||--||---|
> | || || |
> o---| |---o
> | || || |
> |---||--||---|
> || ||
>
> - Franc Zabkar
that's how I read it, C and esr stay the same, and the voltage rating
could be upto 2V, assuming the C is really the same across all 4 caps.
Jeroni Paul
> did you use? I would recommecd using a Panasonic FM series or
> equivalent ultra-low ESR high quality ca fron Nochicon, UCC, or
> Rubycon for something like this.
>
> PlainBill
The failed capacitor is "Jun Fu". I have more of these here and they
have the lowest ESR amongst all I measured (KRG, Nichicon, TL). I
found Nichicon in a local shop but it has higher ESR and heats even
more. For Panasonics I will have to shop online. My ESR meter is of
the needle type so I will not post exact measurements but it lets me
compare quite precisely.
Thank you.
Jeroni Paul
<jamie_ka1lpa_not_valid_after_ka1l...@charter.net> wrote:
> Also, you may want to check or replace the UF "ULTRA Fast" diode in that
> circuit. I found some that developed a leak but not enough to short and
> pass some AC through from the switcher.. This can not only heat the
> diode but the Cap. A simple test is to perform a thermal test on the
> diode.. It should only be warm at best..
Good point, the diode gets very hot, too. Will try to replace it.
Thank you to all.
Jeroni Paul
>
> I = C x dV/dt
>
> Can you use this to estimate the current draw?
>
> - Franc Zabkar
I tried this taking only the fall ramp:
dV = 0,781 V
dt = 4,72 us
C = 1000 uF
It results in 165 A. I may have done something wrong but I think the
capacitor ESR may play a role here as it causes an increase of dV not
reflected at I.
I also noticed the ramp has some ringing in it, not sure if that may
mean something.
The rectifier diode is SR360 and it gets hot very fast in a few
minutes, it could be leaky as suggested by Jamie.
The schematic shown in TNY265 datasheet for a 2A supply on page 9
figure 15 appears to match the circuit.
Thank you.
Phil Allison
"Jeroni Paul"
> "Frank Zabcar"
>
> The current in an ideal capacitor is given by ...
>
> I = C x dV/dt
>
> Can you use this to estimate the current draw?
>
I tried this taking only the fall ramp:
dV = 0,781 V
dt = 4,72 us
C = 1000 uF
It results in 165 A. I may have done something wrong but I think the
capacitor ESR may play a role here as it causes an increase of dV not
reflected at I.
** Sure does !!
An **ideal** 1000uF cap has an impedance of under 1 milliohm at 200kHz -
in reality no such beast exists so the simple formula above fails
hopelessly.
A standard grade 16 volt, 1000uF cap has an ESR of around 200 milliohms ( at
high frequencies) while a low ESR type has about 20 - 30 milliohms and both
have series inductance that amounts to 20 milliohms at 200kHz.
Your 1000uF cap is getting hot cos it has way too much ESR !!!
Get a low ESR type, rated to handle 2 amps or more of ripple.
The Panasonic FM series 16V, 1000uF cap has a rated ESR of 19 milliohms and
a ripple current rating of 2.2 amps.
Note:
The ESR of electros goes DOWN when the cap gets hot - by as much as a
factor of 5.
Means cheap, high ESR electros can be made to do the job in a SMPS at the
expense of having a very short life.
.... Phil