Black vertical lines on ST

[Steve]

Hey guys,

Just hoping for some pointers on this. At first I thought it was a RAM issue but the memory test passes fine on diagnostics and on YAART. Machine is an old rev B ST. Any ideas? Thanks

PXL_20210909_103311924.jpg (379.95 KiB) Viewed 3265 times

PXL_20210910_110658889.jpg (729.07 KiB) Viewed 3264 times

PXL_20210910_110242253.jpg (568.67 KiB) Viewed 3265 times

[czietz]

I recently helped solve a similar issue: https://www.atari-forum.com/viewtopic.p ... 63#p421063. (Of course, in your case it won't be exactly D10, but another data line.)

[Steve]

Thanks @czietz I'll check it out!

[stephen_usher]

Looks like a Shifter issue.

[czietz]

PS: Looking at the pattern on your photo, I suspect D3.

[exxos]

Machine would not boot like that if it was a RAM fault, you basically have one data bit low all the time. I would check out the databus to the shifter or re-solder it etc.

[PhilC]

Machine would not boot like that if it was a RAM fault, you basically have one data bit low all the time. I would check out the databus to the shifter or re-solder it etc.

@Steve That makes sense considering the other stuff we found.

[Steve]

Hi guys,

I've checked D0 to D15 going to U22/26/23/27 pins, everything seems to be connected fine (buzzed them all) I also swapped out all chips U22/26/23/27 with different ones. I also swapped the shifter, still the same.. hmm what am I doing wrong?!

Here's a picture of the lines I've buzzed (highlighted in green spray paint) they all seem fine:

Screenshot from 2021-09-12 19-02-47.png (377.13 KiB) Viewed 3182 times

[PhilC]

@Steve ok so all the lines buzz out ok, good. Now stick your scope on them one by one and one of them is likely staying low, hence the black line.

[DoG]

Check other side of U22, U23, U26, U27.