exxos's Atari, Amiga & retro forum

zChris wrote: 04 Jun 2022 16:17 Darn it still gets trashed. Maybe its important that its 1.2k ohm. What else can one do if that still doesn't help with the trashing ?

It's not just a 'maybe', it's a 'definite'. This was Atari's answer to DMA problems back in the day from their official service guides. Can you please confirm the fixes you've done so far? Because the motherboard bus pullup changes are not the same fix as the DMA pullup.

Steve wrote: 04 Jun 2022 17:15

zChris wrote: 04 Jun 2022 16:17 Darn it still gets trashed. Maybe its important that its 1.2k ohm. What else can one do if that still doesn't help with the trashing ?

It's not just a 'maybe', it's a 'definite'. This was Atari's answer to DMA problems back in the day from their official service guides. Can you please confirm the fixes you've done so far? Because the motherboard bus pullup changes are not the same fix as the DMA pullup.

So far i have replace the 68000 cpu with HC version. Done fix no 3 of the mandatory fixes (10k ohm on DMA buss). Done the reset fix for STe, fix no 11. I did fix no 12 but accidently put 2.2k ohm on P100 which should have been 1.2k ohm.

Alright an update!

I have gotten around to change the P100 to 1.2Kohm. The bad thing now is that i get a black screen. Ive probed the CLK signal to CPU and it seems alright. HALT and RESET are both HIGH, they go low when i press the reset button. There seem to be activity on the buss when i first start it atleast, measured at the CPU. I have reseated all the chips and ram sticks. At one or two occacions i got blue screen, one time a red screen with some horizontal bars, but has happened like 1 or twice out of 40 cold restarts. There are no seeking on the floppy. Tried replace DMA from another board also tried replace the CPU. Both original DMA and CPU are back though.

What's the next logical step to check ?

/zChris

zChris wrote: 11 Jul 2022 23:24 What's the next logical step

Install an IDE interface instead
(sorry.. I couldn't resist)

You have put the resistor pack in the correct way around haven’t you?

stephen_usher wrote: 12 Jul 2022 07:47 You have put the resistor pack in the correct way around haven’t you?

I was thinking the same thing, but you beat me to it :)

Given that you've done quite a lot up to this point, it is probably a good idea to summarise the work you've done so far as a list. The thread is now getting longer, so it would be useful to be able to see where you're at without going back through all the posts.

If you can, add in photos of what you've done.

Also, given the machine is an STE and since you've said the CPU has been replaced, I'd suggest a very close look at any PLCC sockets to be sure they are making a good connection, especially where you've moved chips around.

Alright gang, here is what i have done with this poor board.
At first it didnt give any ouput on the RGB and that was due to a broken resistor which i replace with a cable.

And due to the atari trashing ultrasatan sd card i did the DMA Pullup thing. But since it continued trashing i replaced the CPU with a HC one but that didnt help either.

After that i did buss pullup fix but accidently put 2.2kOhm on P100 where it should be 1.2kOhm. At this point the board was booting up to tos but stilled trashed the SD card.

I left the board until i got 1.2kOhm resistors. When i got those i replaced P100 and after that a blank screen. Once or twice it has been blue or red with artifacts but 99% its black.

Ive been poking around, measured the continuity on the resistors i replaced and there is continuinty there. Ive looked in the CPU PLCC and tried cleaning with 99.7 alcohol and tried to bend out pins i think looked suspicious but to no avail, still a black screen.

Here are some pictures. Some didnt turn out great so let me know if you need any better.

Overview:


Video out fix:


DMA Pullup:


Resistors front and back:


PLCC CPU:

First off your CPU socket contacts don't look great, specifically 6, 15, 19 and 20.

Take a look here and tweak the contacts accordingly: PLCC Contact adjustment

I'd advise you to check other sockets for similar contact conditions, as it doesn't need a lot to cause a bad contact.

For the SIL resistor on the WD1772, it looks fine, but I can't really tell if the dot is at the +5v end, which is where it should be. You should check this with any of the SIL resistors you've replaced.

I also note that all of the SIL resistors around the CPU are black, suggesting you've replaced them all. The only SILs you should replace are those that are orange in this photo:


And those should be 2.2K SILs.


P100 should be left if it is 1.2k, so if you've changed it you may have the wrong amount of pull up going on, this is as per the forum topic: Bus resistors upgrade.

I'd start by checking everything again as per above.

Thanks for your suggestion. I have checked the resistors and they are 2.2 and 1.2, bot happens to be black.

Have tried to straighten the pins in the PLCC. I think these should give good enough contact. And ive used alcohol to clean things out.

PLCC: