Atari 1040STF - C103088 rev.2A - jagged image in low resolution

[dragmar]

I have a problem with Atari C103088 rev. 2A.
Motherboard starts, but often when I start it, I have a jagged image in low resolution.
Changing the resolution to mid-res will restore the correct image.

Diagnosing ram memory with YAART causes many errors to be displayed.

Testing motherboard C103088 rev. 2A Diagnostic cart from Exxosa confirms that the board is working (RAM, GLUE, others IC CHIP).

Could this be the cause of the damaging RAM? or maybe something else?

Exchange 32 DRAM CHIPS somehow I don't see it. Besides, there is nowhere to get them.

I am thinking about launching ST / F / M / MEGA ST-RAM 4MB UPGRADE.
Do I have to remove 32 DRAM CHIPS? maybe it can be bypassed to connect 4MB st-ram from exxos?

In general, the board works, you can play games on a working booster v2.3 - 16Mhz. https://www.exxosforum.co.uk/forum/viewt ... 902#p40902
System failures occur frequently

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[exxos]

Well, you need to at least use a official TOS first, I doubt 104i has had much testing by people. You should always take a machine back to stock while diagnosing stuff.

[dragmar]

I tested the disc on TOS 1.2 and 1.04 (rainbow).

I always do this and only later carry out further tests with extensions or mods (e.g. TOS PP).

I just took pictures with TOS 1.04i already installed.
The disc landed in the closet six months ago because it contained errors. TOS 1.02 was installed

[exxos]

Does YAART pass on stock machine with original CPU ? Does YAART pass on 8MHz mode with the booster ? You must remove the CPU re-locator. Is your PSU recapped ?

[dragmar]

my PSU has not been recapped, I see I need it.
I plan to buy, but it's already after the holidays.
But I checked the ATARI motherboard with another power supply.

The board has been checked without having to re-locate the processor and spare 8 MHz processor.

Not once a demo or game freezes.
And we are talking about 8mhz without re-locate CPU

[Gunstick]

if the ram would be damaged, the games would not work.
So for me this is not a RAM issue.
Rather a timing issue that the shifter gets too much desynchronized from the mmu or glue.
Does the problem persist if you do a reset?
If so, run a demo with overscan effects. Does that correct the issue?

Now for determining what could cause timing issues, I don't know. I guess that @troed or @exxos could help.

[exxos]

If its a timing problem, then this is likely down to noise on the motherboard or monitor maybe don't like low res. Such things are very difficult to track down. You would need to scope H&V sync on desktop and in games and see what the difference is between working and not working. Then do fixes to the machine depending on what the noise exactly is. Some monitors can lose sync on a white blank screen, and then fine once at desktop. But this is again noise issues on the motherboard. My need some better resistors in the sync lines on the video cable...That is probably the easiest thing to try.

[troed]

Yeah .. sounds like a noisy 5V rail - causing memory errors, and Shifter errors. When I overclock the shifter I see exactly such "pixel displacement" - and it can be cured by increasing the voltage (with cooling).

/Troed

[Tomswork]

I agree noise from 5v maybe noise on the ground as well


Tom

[dragmar]

I decided to quickly check the disc by installing 4 MB ST-RAM.
I desoldered the L51 coil and mounted the extension. The YAART test shows that the problem was RAM. There is no jagged picture anymore.
No errors, but as I mentioned earlier, the power supply requires a re-cap. FDD does not start.
I connected GOTEKA and it doesn't start either.
Probably a big load for the PSU is installed ST-RAM, HDD Controller (CT'IDE) and the fact that I did not desolder the RAM memory.

Maybe someone has an idea to disable RAM (1MB), not delete it?

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