Re: Need some help with an Atari Switching Power Supply

This is just a little update. When I removed L6 the +5v came up just fine
and the regulator didn't shut down.
http://games.rossiters.com/manuals/IR-PS2-1.jpg
So the problem is definitely in the audio section of the board. I'm still
trying to find where the problem is. I've replaced the audio amps and some
of the capacitors. I can't find any bad resistors. There seems to be loose
a ground somewhere because if I touch something metal like the coin door
frame or the power switch I can feel a slight tingle of electricity. Not a
huge shock, but enough to be a little uncomfortable. I'm wondering if that
might have something to do with it.

The boards seem to work fine with the ribbon connectors I made. It's
reporting a bad ram, but I'm not going to keep powering the boards up until
I resolve this loose ground issue.

Matt

On Wed, 09 Jul 2008 15:06:49 -0700, Matt Rossiter <matt@rossiters.com>
wrote:
> 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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>>
>>
>
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Received on Wed Jul 16 22:08:32 2008