Fixing an 800XL that used the wrong power supply

[unbibium]

So, suppose you attached a Commodore 64 power supply to an Atari 800XL and turned it on. This kills the 800xl. What components were likely damaged, and is there any hope of repairing it?

 

The red light came on for about a second, and then off forever. Apparently my vivid memories of using a C64 power supply when I was a kid are false.

 

To make this slightly easier to solve, I'm linking to the atari 800xl pinouts in this thread, I googled for the commodore 64 pinouts and the pins seem to be numbered differently since the DIN plug is upside down in some of these diagrams....

 

but I'm thinking I'm not the first person to be this stupid, so maybe there's a well-known remedy that people can already know?

[Bryan]

I've seen this done before and it's not pretty. Here's my advice:

 

1. If the board is mostly socketed, get another working machine (also socketed) and pull everything out of the working machine and put it in the non-working one. If it works, then substitute the old chips in one at a time to see how many still work.

 

2. If the board is unsocketed, it's probably not worth the time to fix it as the voltages from the Commodore supply probably killed several ICs.

 

(using a Commodore supply will put 9VAC on the 5V chips)

[bugs]

***bites tongue***

 

Commodore 64 had dual voltages, so you ran 9v AC though your poor Atari.

 

At the very least your ram chips are probably blown.

 

I believe best sells new motherboards for like 70 dollars.

[fujidude]

I highly recommend this web site. It not only has pinouts and power consumption info for the Atari, it has it for many other systems too.

[Deteacher]

I can totally relate to this story (my condolences, BTW.) I had a similar incident, back in the 90s with my 800xl (may she rest in peace.)

 

I was in college and my 800xl's p/s was dead. Not knowing if I could use my C64 p/s, I took it to my local radio shack, along with my 800xl. Hey, I have questions...they have answers, right?

The guy behind the counter takes a look at the specs on the computer...then the C64 p/s and then says "It looks like it should work just fine."

 

So, I headed back home, hooked it up, threw the switch. I remember the most god awful sound came out of my TV for about 2 seconds...then snow. I just killed my Atari 800xl.

 

So, I went back to Radio Shack, found the same guy and told him what happened. I remember demanding some kind of restitution, like 1/2 the cost of the repairs. His reply to me was "Hey, nobody put a gun to your head and told you to try it." I was never so mad at anyone before in my life.

 

The moral is: "You've got questions...they've got answers...and a wrong answer is still an answer."

[Rybags]

It would be interesting to know for real just what components die when you do this.

 

I do suspect though, that just about every IC on the board becomes unusable.

[BillC]

It would be interesting to know for real just what components die when you do this.

 

I do suspect though, that just about every IC on the board becomes unusable.

9VDC would be bad enough, but discrete transistors can literally explode when powered with reverse polarity. With AC power ICs would be subjected to reverse polarity 50 to 60 times a second. Polarized capacitors don't like reverse polarity either, they can also explode.

 

Best to get a replacement 800XL board(less expensive than ordering just the Atari custom ICs, $20 for only POKEY), if desired you can test each IC from the old board in the new one to see if any survived.

[RodLightning]

Are there any significant risks in temporarily swapping suspect ships (Antic, GTIA, Pokey, CPU, PIA) onto a working motherboard? I have done it in the past with no ill effects on the XL machines, but always worried about support chips and components. Is it possible for any of the main chips to be so burned that it would cause damage elsewhere?

 

This applies to cases where both boards are socketed of course and swapping chips around can be done in a few minutes instead of hours.

[Bryan]

There's not much risk, as long as you turn it off as soon as you know it isn't working so you don't have long-term bus contention.

[+tf_hh]

Hi,

 

maybe it sounds crazy, but I suggest to try repair it. A few years ago I buy a ebay lot containing over 10 XE mainboards and 800 XL Mainboards plus a few case (parts). Also three power supplies... for C64

 

You can imagine, I know really good when opening the box what happens to the boards... nothing of them runs. ALL boards has defective RAMs, and most of the DRAMs are getting hot as hell in seconds. The typical problem when an Atari XL/XE was "commodorized" by a C64 power supply. I change all 16 DRAMs of a 130 XE mainboard and... all fine, this computer works without any issue in a 12 hour loop test using the CPS SALT test fixture.

 

Because I´ve a lot of boards working after changing DRAMs, I do some strange tests.

 

So I connect an old C64 power supply (the first model looking like a door stopper) with Ampmeter and Voltmeter and measure voltage at some points. Of course the boards was flooded with 9V AC, but for example at ANTIC and PIA only 1,7 Volt AC appears. The big amount of power was consumed by the DRAMs. This is logical, because the DRAMs power rail is directly after the power switch. Current drops down to approx 500 mA, because the 9V AC part of the C64 power supply isn´t very strong. In the longest test I connect it for 10 minutes... DRAMs began to smoke, but all Atari custom chips survived. Only two TTL ICs was burned, too. But 10 minutes...

 

All of these boards were repaired successful. Only two customs chips were killed also, one Freddie and one CPU. But issues with CPUs are not so rare, so it maybe random.

 

Try it! Change all DRAMs... the chance to win is 50:50 I would say.

 

Jurgen

 

[unbibium]

Well, I brought it back to my local hackerspace, where I have my working Atari power supply. It turned on, but video was a black screen. I took out the 32-in-1 WarpOS upgrade and put the factory ROM back in, and same result. The DRAM chips are the eight identical-looking chips on the left, right? I noticed those were all very hot to the touch. So I think I will swap them out. I'll keep you posted.

[Rybags]

Black screen is a good result - means that it's fairly likely that GTIA is fine, CPU probably good and OS Rom OK.

If the screen doesn't roll like old TV with V-hold out, means Antic is probably good too.

Edited April 5, 2016 by Rybags

[Willsy]

Black screen is a good result - means that it's fairly likely that GTIA is fine, CPU probably good and OS Rom OK.

If the screen doesn't roll like old TV with V-hold out, means Antic is probably good too.

Yes. It just doesn't have any ram to maintain a display with, and the dead DRAMs are probably holding the address and data busses in goodness knows what state, so the CPU is just reading garbage at the data bus. I say change the DRAMs.

 

Oh, one more thing: THROW THAT C64 BRICK IN THE TRASH!