Hello,
I have an Atari 800 XL which has some strange issues.
Normal cardridges are working, but when I try to use the 8MBit cardridge, the problem is following:
The game menu is shown, but Atari crashes at any game start.
Flashing of the cardrige results in verify failed errors.
RAM test is okay.
Another Atari 800 XL works fine with the cardridge, as for flashing and for loading games.


So I think something in my Atari is broken.
What could be the problem? Thank you in advance

Good question, could be anything.

Signals to/from the cartridge are managed by the MMU and the memory-logic.
Perhaps the delay-line is going bad and setting signals with the wrong timing.
That is what I would replace first.

So am I right, it is the Chip U29 (C060472) or maybe a cap beside it?
If it is the chip, where can I get spare parts? Thank you so much

Yes, that is the one.
Google says it's an EP8212 delay-line re-branded to this atari-number.

I use scrap-boards most of the time.
Best electronics (USA) surely has them.

A guy on FB made a replacement version.
https://www.facebook.com/groups/3902506 ... 2357717579
Robert de Boer.

Success.
Sijmen.

Thank you, I asked there for spare parts, hopefully I get my Atari working In the meanwhile I will check all the resistors and caps in that region, maybe I am lucky and there is a faulty one there.
The FB link is not working, unfortunately.

Okay, I did some measurements:

R13 = 0.66 (nom. 1K from my scematics)
R20 = 0.68 (nom. 3K)

Can this also be the problem?

I could search them, but I am not going to look for a needle in a haystack.

So better make a picture of your schematics and circle the parts.

Thanks!

R13 is the first Resistor in the row left from the MMU, R20 is the Resistor right under the Delay Line Chip. Attached the location on the board.
I checked two independent schematics for these resistors and both claim R13 to be 1K and R20 to be 3K (and also the color rings suggest that).
But I don't know if in inner circuit measure the values might somehow drop to 0.66 or 0.68 K?
If on another working Atari, the values are measured 1K and 3K my first repair attempt will be to replace these resistors.

Edit: in another working Atari the values are about .75

R13 (cartridge select pull-down), remove GTIA and MMU, measure again.
Compare with R14, should be both 1k.

R20 (phi-2 pull-up), remove CPU and U18 and U19, measure again.
No compare, should be 3k.

If IC's are soldered, remove resistor and measure detached.

Hello, thank you for the suggestions.
I talked to best electronics and they asked me similar things:
- To install a socket for the MMU and swap it between the two Ataris.
- To clean the board from all rust, because this also could have some conductive effects (the pre owner had put liquid inside, so it was kinda rusty).

At this moment, I think the resistors are okay because of the low values on the working Atari, the ICs seems to form a parallel resistor effect. So I will remove all the socketed chips and clean them, and will brush over the whole board one more time to get rid of all the rust.

Shipping to germany is around 40 USD, and also 10 for the chip. So it would be cheaper to buy a "new" one

To rule out something simple, like the CPU is almost burned-up....
Replace the CPU with the good-800XL and see how it works then.
Most likely, resistors, do not go bad. Capacitors do, very rarely the flat type, most commonly the electrolytic.
Chips do rot inside when sealed badly due to production flaws, so go check that first.
You could do the same with GTIA and MMU from the good system and see what it does.
Where are you in Germany?
Grtz, Sijmen

Unfortunately I don't own the working Atari, it's my brother's one, which I only had for measurement for one day.
I took all Chips out of their socket and cleaned it but the result stay the same.
On both Ataris the MMU has no socket. So I wanted not to risc the health of the good one by soldering it out just for testing.
I live in Baden-Württemberg, apprx 30 km away from Stuttgart.
Kind regards
Thore

As alternative source, you can contact the ABBUC, the german atari-club.

Yes, Germany is big, I though if you live just over the border from the Netherlands we could meet up and fix this problem.

Anyhow, try the ABBUC, they have lots of members and many of them have parts lying around.

Grtz,
Sijmen.

I already had a look at the ABBUC site but due to a hacker's attack, the site is only a stub right now, and I cannot find a contact address.
But... I am thinking about creating new MMUs (and I am sure by 95% that this causes the problem). As I read there is the JED file in another forum, and the chip is compatible to the 16L8 GAL as far as I know. Maybe it is worth to test it, as this might close the gap of the chips being extinguished.
I need some time to get all parts and rebuild the machine, but I will post my results here. Without any guarantee that this will work

I tried to put the MMUPAL JEDEC to a PAL 16L8 chip, but my programmer tool does not have this chip in the list, so I think I killed two PAL chips so far by falsely using ATF16V8B?
I use a TL866ii Plus with XGecu software.
Unfortunately the tool PALTOGAL does not work anymore (only 16 Bit?) and so I cannot convert it to use a GAL Chip.
Does anybody have a GAL JEDEC file for the MMU?
Or if somebody knows the correct PAL Chip for use in XGecu.
Thank you in advance