Re: Need some help with an Atari Switching Power Supply

To test this power supply you must have a load on the 5 volt supply.
With out a load it will not function correctly.

On the test bench check R54 and R55 to make sure they are OK
Then connect a jumper across R54 (make R54 a short) and another jumper across R55.
Connect two Auto #1156 bulbs ( 12 volt car brake light bulbs ) to the
5 volt supply (J6 pin 10 for +) and (J6 pin 14) for ground.
These bulbs should be in parallel with one another.
This will give a load of about 2 amps.

The 5 volt supply is the only one that needs a load.
The -31.5 , +15 , and +145 will all function correctly with just
a load on the +5 volt supply.

Power on the supply and start checking with a scope.

If it is still in shutdown mode. Power it off and
>From what you have said I would start with the -31.5 supply
To check the audio section just remove L6 then power up
to see if it works. If it works then audio section is bad.
If not check BR4, R42, R43, C29, and C31

If still not working check CR8 and CR9.
Then tell us the voltage at the following locations
U2 pin 6
U2 pin 7
U2 pin 1
U2 pin 4
U2 pin 5
U2 pin 2

Tim

-----Original Message-----

>Subject: Re: RASTER: 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 Wed Jul 9 17:46:48 2008