Testing Atari XL/XE power supplies

[Pilsner73]

Getting back into the Atari 8 bit computers and remember how their power supplies could cause many problems back in the day so would like to make sure I'm testing them correctly before any serious use of the computers. I do know to avoid the ingot version (3) of these. I am using this diagram for pinouts http://www.faqs.org/faqs/atari-8-bit/faq/section-17.html

 

I have a radio shack auto-range digital multimeter (22-163) which I plugged the black probe into the -com and red probe into +v, i then leave it auto sensing and set for volts and the - with three dots under symbol (not the ~).

 

So to test I would take the black probe to the ground pins (7,5,3) and red probe to to the +5v(6,4,1) pins to make sure each of them was at or very close to 5 volts. Correct?

 

Now if the power supply is reading a steady 5 volts or so on those pins is there anything else to test (amps/ohms) and if so how does one test for that?

[Rybags]

To test Amps you need the thing under load, ie running something, plus the meter has to be in series, which is a bit harder to do.

 

The problem with the bad PSUs seems to be them going over-voltage.

 

Best thing might be to just run the computer while it's opened up, then test points within the machine. Use part of the ground plane that surrounds the motherboard, then check the voltage on a +5 volt source at the back of the Atari's power input with the machine turned on.

[zylon]

I use a car tail light bulb for testing A8 and C64 power supplies. I hook it up on the +5 and ground pins and let it run about a half hour. If the voltage goes above 5.2, I don't use it.

[Pilsner73]

I use a car tail light bulb for testing A8 and C64 power supplies. I hook it up on the +5 and ground pins and let it run about a half hour. If the voltage goes above 5.2, I don't use it.

 

So do you hook the light bulb to the 5v pin only or do you run a ground also? Then for the testing where do you have the multimeter probes hooked to?

[zylon]

I use a car tail light bulb for testing A8 and C64 power supplies. I hook it up on the +5 and ground pins and let it run about a half hour. If the voltage goes above 5.2, I don't use it.

 

So do you hook the light bulb to the 5v pin only or do you run a ground also? Then for the testing where do you have the multimeter probes hooked to?

I'll set it up later on one of my supplies and upload a pic.

[zylon]

My setup is crude but effective. In the case of C64, you have +5vdc and 9vac. Hooking up the light to the 9vac, it'll either be there or it won't. On the +5vdc side, you might find weak caps which will take some time to build voltage or you may find that the regulator fails when it gets hot. I've seen plenty of supplies which work fine till they warm up. +6vdc is the max voltage for RAM chips(on c64). The DC side is what kills chips. I let them run with a lamp load for a half hour or until warm. The one pictured runs at 3.8-4vdc until warm then runs at 4.8vdc. The auto lamps use about 1amp and provide a visual indication as they'll get much brighter as voltage rises.

On this supply, I have it hooked to ground pin and +5vdc pin. I'm using 2600 joystick cable connectors with a slight crimp. They fit well on the pins and are handy. The leads are clamped to the connections on light socket. No vintage computers get hurt this way.

Edited March 6, 2011 by zylon

[+wood_jl]

Zylon, that's a really cool idea.

[Pilsner73]

Thanks for the great description and pictures. With old power supplies we need a way to make sure they can put out the power the system requires and also handle a load for a good length of time.