Re: Need some help with an Atari Switching Power Supply

Hi Solarfox, thanks for responding...

I've been trying to trace this problem down over the weekend.

Here's a little update. It looks to me like the problem is in the audio
amplifier section of the board.
After a little bit of frustration I decided to disable pin 10 on the
regulator and just see what happens under load (something I normally don't
recommend you try at home). Lifting up pin 10 on the 3525 regulator
essentially means it *won't* shut down until I cut the power.

Well, Capacitors C37, C48 and C58 all popped. They are along the -31.5v
supply line. The TL082 and TDA2030 amps had already been replaced prior -
so they should have been fine. As far as I can tell they didn't burn out,
but I will confirm that later.

I highlighted the exploding capacitors in red. Apparently you can strap
the board for +31.5v or -31.5v (highlighted in blue). W18 is currently
strapped to ground and W30 is currently strapped to -31.5v. The schematics
show it the opposite way as you can see. Normally capacitors explode when
they are in backwards - so it makes me wonder if the board is strapped
wrong or if the capacitors need to be oriented the oppposite way. I
believe the board is strapped correctly. I'm a little confused. Anyway,
there appears to be something wrong with the -31.5v supply. There doesn't
appear to be a short across the capacitors.

http://games.rossiters.com/manuals/IR-PS2-1.jpg
http://games.rossiters.com/manuals/IR-PS3-1.jpg

And of course the service manual is here with a small description of the
audio section.
http://games.rossiters.com/manuals/Atari_Switching_Power_Supply.pdf

To answer a couple of your questions,

1) Yes, the independant 12volt line still stays up even when the regulator
shuts down.
2) Yes, I've been using a isolation transformer with my oscilloscope - so
no sparks with those transistors.

Thanks for all the help. Hopefully I can figure out what's wrong with the
audio amplifier. :)

Matt

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Received on Mon Jul 7 18:12:11 2008