1040 STF showing occasional rogue pixels

[sandord]

The error shown is in bit 13:
0xFFDF = 1111111111011111 was read, but...
0xDFDF = 1101111111011111 was expected.

If the error always is in bit 13 (the errors you previously posted were and also the speckle pattern looks reasonably repetitive to me), then you know which RAM chip to change.

PS: Even though I gave it some thought, I'm still puzzled by which effect the RAM access speed could be halved.

Thanks for sorting that out. I don't know how the memory layout works exactly but could it still be only one chip if you take the fact into account the the same problems appeared when disabling the second half of RAM (bank 1)? The speckles appear at the end of the RAM, where video memory is located so that would sound like the second bank to me. The ST has these SMT rams, they look really hard to replace. And are they even sold a piece these days?

[czietz]

Sorry, I had missed that it also happened when the upper bank was disabled. It's indeed unlikely that two RAM chips (for lower and upper bank) are bad. It then points more into the direction of the buffers (74xx373, 74xx244), but on the other hand defective buffers cannot explain why the errors primarily happen in the last kilobytes of RAM.

[exxos]

Did you try the freezer spray ?

[sandord]

Did you try the freezer spray ?

Yeah, I hit all of the ram and the CPU, MMU, GLUE, buffers, shifter. It didn't seem to make any difference. Honestly, I didn't want to deplete the complete can, since it's quite expensive. So I sprayed the said components for only a second or two each (I did give the RAM section about 5 sprays I think).

[exxos]

Yeah, I hit all of the ram and the CPU, MMU, GLUE, buffers, shifter. It didn't seem to make any difference. Honestly, I didn't want to deplete the complete can, since it's quite expensive. So I sprayed the said components for only a second or two each (I did give the RAM section about 5 sprays I think).

What speed are the DRAMs ?

[sandord]

What speed are the DRAMs ?

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I'm not sure how to tell but I figure the picture says it all?

[exxos]

I'm not sure how to tell but I figure the picture says it all?

150ns likely. I would solder a wire over L51 (next to PSU connector) and see if that does anything. Next change the 33R resistors with 68R and see if that does anything..

Very odd issues indeed...

[sandord]

150ns likely. I would solder a wire over L51 (next to PSU connector) and see if that does anything. Next change the 33R resistors with 68R and see if that does anything..

Very odd issues indeed...

Running YAART with a wire over L51 for over 3.5 hours now. No bad pixels or memory test errors at all. Promising, but I'll leave it running for a few more hours.

[exxos]

Running YAART with a wire over L51 for over 3.5 hours now. No bad pixels or memory test errors at all. Promising, but I'll leave it running for a few more hours.

Fingers crossed!

[sandord]

Running YAART with a wire over L51 for over 3.5 hours now. No bad pixels or memory test errors at all. Promising, but I'll leave it running for a few more hours.

Fingers crossed!

7 hours, 122 passes, 0 errors and no bad pixels! This is looking gooood!
If only we didn't have the 50% RAM speed problem :cry: