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Dizzy

Atari 800 strange problem ...

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Weird. Remember though, brown screen tends to indicate that the machine isn't even getting to the point of starting the OS.

 

Antic you can swap from an XL. Antic is unique to PAL/NTSC but there is also a later Antic made for large memory >=128K machines but should work fine on others.

GTIA should be unique only to PAL/NTSC.

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Is your new 800XL NTSC or PAL?

 

If it's PAL, then you can swap everything. If you put a good 6502C in and it didn't work, then I'd guess the system timing is marginal. GTIA divides the main clock for the CPU and Antic.

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Just remember that you can NOT swap a 6502B and a 6502C (C014806) chip. It is perfectly acceptable to swap the entire CPU card (no matter which type CPU is on it), though.

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Just remember that you can NOT swap a 6502B and a 6502C (C014806) chip. It is perfectly acceptable to swap the entire CPU card (no matter which type CPU is on it), though.

 

Yes, but I don't understand why I get the same result when swapping my 6502C with another 6502C, and when swapping my 6502C with a 6502B ... To me the result should be different, and I even more don't understand why the original Atari 800 6502C is working better than the 6502C of my Atari 800 XL ...

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Yes, but I don't understand why I get the same result when swapping my 6502C with another 6502C, and when swapping my 6502C with a 6502B ... To me the result should be different, and I even more don't understand why the original Atari 800 6502C is working better than the 6502C of my Atari 800 XL ...

This is usually the indicator of some other component which is causing marginal timing. I was working on a 130XE once for a customer, with a marginally bad FREDDIE, and it wouldn't boot up at all (red screen). I swapped the FREDDIE to a good 65XE, and it seemed to work there, but when I swapped the FREDDIE from my 65XE into the 130XE, now the 130XE worked as well. Later, after more extensive testing, the marginal FREDDIE was found to also crash the 65XE, just not immediately. I'm not sure exactly what's wrong with that FREDDIE, but it seems to work more or less depending on what Atari it's in. Without extensively looking into the timing of the signals, you'll never know what exactly is wrong, but you can be sure that it's a marginal component, and that it's bad.

 

I suspect some component in your non-working 800 CPU board is the same way. Whatever the marginal component is, it works with *that* particular 6502C for a short while, before it crashes, but with others the timing is too far off for it to work. Assuming the 6502C from the 800 works fine in the 800XL, then you need to start looking elsewhere for your issues. Given that a different CPU card seems to work, it's probable that the issue is on the CPU card, but maybe not. The CPU card you tried is of a different design, and may be less susceptible to marginal timing issues than the 6502C based CPU card.

 

If your 800XL is socketed, I would suggest you take your known-working 800XL, and your bad 800 side by side, and swap LSI chips one at a time. Then check each machine to see if they now function differently. Afterwards, swap the chips back, and do the same for the remaining LSI chips. If you rule out all the LSI chips, you're going to have to start working on the smaller MSI and SSI chips (the 7400 series logic). Again, after each swap, check behavior for differences, and then swap back if there's no change, and continue. In this case, you're primarily looking for a chip swapped from the 800 that causes the XL to stop working correctly, as it's harder to prove the 800 *is* now working correctly.

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Yes, but I don't understand why I get the same result when swapping my 6502C with another 6502C, and when swapping my 6502C with a 6502B ... To me the result should be different, and I even more don't understand why the original Atari 800 6502C is working better than the 6502C of my Atari 800 XL ...

 

Be careful, I'm pretty sure I've seen you use 6502C and 65C02.. They are also very different chips...

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A 65C02 will replace a 6502B, but NOT a 6502C. I know it sounds a little complicated. Think of the 6502C as 6502Custom. It is custom made for Atari, and therefore different. It is labelled C014806.

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The problem is getting even more weird ... Here is what was the situation before today :

- When I turned on my PAL Atari 800, the Atari was crashing after a few seconds of use, but only when using BASIC / NOTEPAD / or floppy disks. When I was running games cartridges, everything was fine.

- When I swapped the CPU card from an NTSC Atari 800, then no crash anymore (except of course the displayed colors which were wrong due to NTSC/PAL incompatibility).

- I tested ANTIC / GTIA, they seemed to work fine. So I ordered a new 6502C, but when I swap it I get a brown screen at startup.

 

So I thought the problem may come from another component on the CPU board. So I finally ordered a new PAL CPU board. I tried it today, but when I startup the 800, I am still getting the brown screen !

So I decided to put back the old PAL CPU board, and now I am still getting the brown screen at startup even with this board !!!!!!!

 

I don't understand why the situation is getting worse ... Finally my problem does not seem to come from my CPU board, I now need help from an Atari 800 expert to tell me what means a brown screen at startup ....

Anyone knows ?

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OK, so I will give the "expert" answer to myself : a brown screen at startup means that the Atari 800 does not find the OS ROM ... How do I know it now ? hummm .... well .... I feel very very very stupid ... When I was doing my last tests about CPU swaps, I did not put back the OS ROM into the Atari ... AAAArrrgghh !!!! Sooooo Stupid I am !!!!!!! :mad:

So I re-did all my tests, the conclusion is : what was causing the Atari to crash after a few seconds of use (except when playing with games cartridges) was the 6502C on the CPU board.

As I already ordered a new 6502C alone, I could swap it with my bad 6502C to let my CPU board work fine. So I ordered a new spare PAL CPU board for nothing ... :mad: I will have now to sell my working spare PAL CPU board ...

 

Thanks to all of you for the help you provided to me !

Edited by Dizzy

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