Author Topic: Commodore 64 Power supply into an Atari 800XL  (Read 2674 times)

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Offline 00WReX

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Commodore 64 Power supply into an Atari 800XL
« on: 07:10, 25 August 14 »
Hi all,
 
Looking for any advice from the knowledgable technical people out there.
I just picked up a really nice (boxed) Atari 800XL PAL version.
The only problem is, the previous owner attempted to test it with his
Commodore 64 power supply  :o  (I new this before I got it...wish he had just
given it to me without trying to test).
 
As you may or may not know, the c64 & Atari 600/800XL both use the exact
same 5 pin din power connector, but that is where the similarities end.
They both supply 5v (on different pins) and the C64 supply also provides
9 volts AC. If the Atari was not dead before he plugged this in, it
certainly was after... ::) >:(
 
The symptoms are simply a dead computer (except for the power on LED).
Anyway, as luck would have it this is an early 800XL and every single IC
on the board is socketed.

I initially did the 'feel' test to see if any IC's were hot, and I found
a couple of RAM and the MMU to be quite hot.
I replaced all the RAM with known good RAm and also burnt a GAL for the MMU.
I have an ATARI 600XL that is also fully socketed (working) and I previously
had to replace the MMU in that with a GAL and the 600XL works great.
 
Anyway, the new RAM & MMU made no difference so I proceeded to swap every IC
into my working 600Xl one by one. They all worked.
 
Anyone done a repair on an Atari 600/800XL where a C64 supply has been plugged in ??
 
Any ideas on what the 9VAC would kill ??
 
I have gone over the board very carefully under a good light on both component
& solder sides and all looks good. I have tested for 5v at each IC and can confirm
it is present.
 
I have the 'Atari 800XL_Sams_Computerfacts_Technical_Service_Manual' which is great
but I do not have a scope, so I'm limited a fair bit.
Considering all the IC's appear to be fine that basically only leaves the RF modulator,
resistors, diodes, capacitors, a handful of transistor's and a couple of crystals.
 
Any thought's / suggestion's / previous experience appreciated.
 
Cheers,
Shane
 
The CPC in Australia...
Awa - CPCWiki

Offline Grimmsqueaker

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Re: Commodore 64 Power supply into an Atari 800XL
« Reply #1 on: 12:09, 25 August 14 »
The c64 supply itself could have been a dodgy one, you look on Lemon and the C64 supplies are apparently quite notorius for giving out and allowing the full whack of the mains to travel through onto the board instantly frying your C64.

Could maybe be the TV out modulator or possibly the actual power in connector and circuit associated with it on the board itself, I would check any resistors, capacitors etc round that area to see if anything there has blown or melted.

Offline Bryce

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Re: Commodore 64 Power supply into an Atari 800XL
« Reply #2 on: 12:54, 25 August 14 »
Hi 00Wrex,
      Unfortunately, like the CPC the 800XL doesn't have any voltage regulation inside the machine, it's all done in the PSU (other than a few capacitors and inductors in the computer). The 9VAC would have gone to pin 6 (+5V on 800XL) and 7 (GND on 800XL). It also put 5V on pin 5 (GND on 800XL) and possibly pin 4 depending on which version of C64 PSU it was. This could have fried several things inside the Atari, but may not have, because it probably killed the C64 PSU instantly. If you are getting 5V to all ICs, then I suspect you may have fried the modulator and the Atari still works. Can you connect it via S-Video to see if you get any picture there?

Bryce.

Offline 00WReX

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Re: Commodore 64 Power supply into an Atari 800XL
« Reply #3 on: 16:14, 25 August 14 »
Thanks for the replies.

I did actually get the Commodore 64 power supply with the Atari, and I tested the voltages.
They were OK and nothing bad...5.12v and around 10VAC unload which is pretty normal (even ran a C64 on it for half an hour).

I will need to work out how to best connect it up via s-video / component.

I'm assuming the current monitor output signals are derived from the RF modulator, so if the RF mod is gone then so would the monitor out ??

Cheers,
Shane

The CPC in Australia...
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Offline Bryce

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Re: Commodore 64 Power supply into an Atari 800XL
« Reply #4 on: 22:55, 30 August 14 »
If the PSU is ok, then maybe the Atari was already damaged before he tried to test it?
It's the other way around with the video, you never derive anything from RF, it's the end of the chain and the worst quality. The monitor output is one stage earlier.

Bryce.

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Offline 00WReX

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Re: Commodore 64 Power supply into an Atari 800XL
« Reply #5 on: 15:01, 05 September 14 »
I decided to test all the original RAM from the Atari and found 4 of the 8 RAM IC's were dead.
I then went back and tested my 'known good RAM' (last tested a few years ago) and found 2 were dead  ::)
Replacing the 2 dead with 2 good from the original 4 that tested OK and the Atari fired up.

All appears fine and everything that I have tested is working as it should, and I have had the computer running for over an hour now.

So in the end the MMU & 4 RAM IC's were dead.

Cheers,
Shane
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Offline Bryce

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Re: Commodore 64 Power supply into an Atari 800XL
« Reply #6 on: 16:18, 05 September 14 »
Good stuff. At least it works again :)

Bryce.

Offline 00WReX

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Re: Commodore 64 Power supply into an Atari 800XL
« Reply #7 on: 01:14, 08 September 14 »
Thanks Bryce for the replies, much appreciated.

Must say, I really like the feel of the 'Alps' keyboard in the 800XL  8)

Cheers,
Shane
The CPC in Australia...
Awa - CPCWiki

Offline Bryce

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Re: Commodore 64 Power supply into an Atari 800XL
« Reply #8 on: 10:29, 08 September 14 »
The XL range had a great keyboard, pity the messed it up (went cheap) on the XEs :(

Bryce.