Re: Need some help with an Atari Switching Power Supply

Thanks Tim!

These are great suggestions and I will definitely try them out. Much
better than disabling the shutdown pin on the regulator. :)

I think I may have found the culprit. One of the two capacitors, C29 and
C31, is bad. I believe it's C31. I don't get any reading on it with my
capacitance meter.
I'm waiting for my order of parts to come in. Once the replacements are
back in - I will try your method.

At one time I used a single IC to put a 5v load on the power supply and it
still shutdown. Apparently it doesn't like any load at all.

I will let you know in a day or two how it goes.

Matt

On Wed, 9 Jul 2008 17:46:40 -0400 (EDT), teeray <teeray@earthlink.net>
wrote:
>
>
> 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 18:06:55 2008