opening the 2c brick psu
phil
problem.the plastic welds are not easy to find. Has anyone else done
this before?
Also, as a temporary replacement, I tried a 12v 2a psu. It couldn't
provide enough voltage pressure, (i know it's supposed to be 15V) I
think the high current the machine drew from the 12v psu may have
blown the fuse on the board. F1, the little green thing. Does anyone
know the value of the fuse? Thanks.
Michael J. Mahon
The //c power brick supplies 15vdc at 1.2A, and the //c itself is
pretty tolerant of voltage. It will run very nicely from a 12v
battery, for example.
You don't mention whether the 12v power supply you used was regulated,
or what the actual voltage was when the //c was switched on, but if it
can supply 12v under load, it should work.
It think you are correct to suspect some other problem with the //c.
Sometimes fuses blow because of fatigue, and sometimes they blow
because too much current is being drawn. It's worth finding out
which is the case before risking further damage.
It's also likely that the "brick" can be fixed by replacing an
internal fuse, assuming that the problem was an overload.
-michael
NadaNet networking for Apple II computers!
Home page: http://members.aol.com/MJMahon/
"The wastebasket is our most important design
tool--and it's seriously underused."
phil
>
> You don't mention whether the 12v power supply you used was regulated,
> or what the actual voltage was when the //c was switched on, but if it
> can supply 12v under load, it should work.
When I crimped the strain relief in the back of the power in DIN plug,
It shorted the plus with the housing ground, so plugging in the lead
in shorted my 12V psu. Oops. The fuse f1 (yellow, behind power switch
inside 2c unit) did pop also, so if anyone knows what to replace it
with, that would be good. I'm using a 2A one for now...
My 15V brick outputs no power at all, so if anyone can please give me
a hint on where the plastic casing is welded together... Thanks.
Roger Johnstone
>
>>
>> You don't mention whether the 12v power supply you used was regulated,
>> or what the actual voltage was when the //c was switched on, but if
>> it can supply 12v under load, it should work.
> OK, I found the problem..
> When I crimped the strain relief in the back of the power in DIN plug,
> It shorted the plus with the housing ground, so plugging in the lead
> in shorted my 12V psu. Oops. The fuse f1 (yellow, behind power switch
> inside 2c unit) did pop also, so if anyone knows what to replace it
> with, that would be good. I'm using a 2A one for now...
According to the Apple IIc Technical Reference Manual it's a 10 amp fuse.
That seems ridiculously high to me, but it doesn't look like a
misprinting and 1.0A would be too low. The manual says the internal
switching power supply can run from 9V to 20V and consumes a maximum of
25W, so at 12V it could draw peak currents of around 2A.
Check that the diode CR1 isn't shorted. It's a reverse polarity
protection diode connected from the positive to negative supply input
lines immediately after the fuse.
> My 15V brick outputs no power at all, so if anyone can please give me
> a hint on where the plastic casing is welded together... Thanks.
I had to open a IIc power brick up a few years ago. From memory the two
plastic halves are glued together around the entire seam. I used a vice
to repeatedly squeeze the brick around the seam until it broke and I
could get a screwdriver in to lever the two halves apart. The only other
option is to use a fine-bladed saw to cut it open. Designers (or
accountants) who save a few cents on screws by glueing cases together:
first against the wall when the revolution comes!
--
* Roger Johnstone, Invercargill, New Zealand -> http://roger.geek.nz
* PS/2 Mouse Adapter for vintage Apple II or Mac
* SCART RGB video cable for Apple IIGS
Michael J. Mahon
> In <1176613311....@o5g2000hsb.googlegroups.com> phil wrote:
>
>>>You don't mention whether the 12v power supply you used was regulated,
>>>or what the actual voltage was when the //c was switched on, but if
>>>it can supply 12v under load, it should work.
>>
>>OK, I found the problem..
>>When I crimped the strain relief in the back of the power in DIN plug,
>>It shorted the plus with the housing ground, so plugging in the lead
>>in shorted my 12V psu. Oops. The fuse f1 (yellow, behind power switch
>>inside 2c unit) did pop also, so if anyone knows what to replace it
>>with, that would be good. I'm using a 2A one for now...
Glad you found the problem. That shouldn't have blown the //c fuse,
though. Have you checked the original brick after replacing the fuse?
(Or, *maybe*, some fault in the brick is what blew the fuse in the
first place...)
> According to the Apple IIc Technical Reference Manual it's a 10 amp fuse.
> That seems ridiculously high to me, but it doesn't look like a
> misprinting and 1.0A would be too low. The manual says the internal
> switching power supply can run from 9V to 20V and consumes a maximum of
> 25W, so at 12V it could draw peak currents of around 2A.
I haven't checked the schematic, but I would expect there to be a
large-value electrolytic capacitor just past the power switch and
fuse (probably inside the power supply). The high value for the fuse
may be used to prevent early fuse fatigue due to repeated inrush
current surges.
In steady state, 3-4 amps should be fine.
My recommendation would be a 4A Slo-Blo fuse.
> Check that the diode CR1 isn't shorted. It's a reverse polarity
> protection diode connected from the positive to negative supply input
> lines immediately after the fuse.
Assuming thats a power diode (1A or more forward current), then it
should quickly blow the fuse if a reversed supply is attached,
protecting itself from overtemp damage.
If I wanted to blow that diode, I'd apply a high DC (or AC!) voltage
of the *expected* polarity, to cause it to break down in zener mode.
Then in less time than the fuse could blow, the diode would be toast.
Of course, the internal power supply would also be toast. ;-)
>>My 15V brick outputs no power at all, so if anyone can please give me
>>a hint on where the plastic casing is welded together... Thanks.
>
>
> I had to open a IIc power brick up a few years ago. From memory the two
> plastic halves are glued together around the entire seam. I used a vice
> to repeatedly squeeze the brick around the seam until it broke and I
> could get a screwdriver in to lever the two halves apart. The only other
> option is to use a fine-bladed saw to cut it open. Designers (or
> accountants) who save a few cents on screws by glueing cases together:
> first against the wall when the revolution comes!
I hear you! But, as you can imagine, sealing line voltage circuits
is regarded as a virtue in the consumer electronics world.
heuser...@freenet.de
> Roger Johnstone wrote:
> > In <1176613311.401890.12...@o5g2000hsb.googlegroups.com> phil wrote:
> >
> > Designers (or accountants) who save a few cents on screws by
> > glueing cases together: first against the wall when the revolution comes!
>
> I hear you! But, as you can imagine, sealing line voltage circuits
> is regarded as a virtue in the consumer electronics world.
There are other solutions to this problem. Nintendo for example
uses some funky screws for their consoles and power bricks.
Common households normally don't have drivers or bits for them.
The bits cost only a few Dollars/Euros and a dedicated person
can acquire and use them to open the cases without damage
while curious Johnny-five-years-old stays off limits.
bye
Marcus
Michael J. Mahon
I prefer this approach, too--and it only costs a few cents more.
I suspect the root of the problem is that these "bricks" are seen
as non-repairable units by the manufacturer.