1040 STF shifted video

[sandord]

So, I've got another 1040 STF (C103175) in the mail last week (only the bottom part that is, no keyboard or cover).

Today I tried if it worked.

Now that lead to a little surprise: the video output seems shifted somehow. That is, only certain planes and it's not consistent across cold starts either (see different colours below).

In medium resolution the effect is the same, one plane is shifted from the other.

See for yourself:

IMG_20181110_151741.jpg

IMG_20181110_151533.jpg

IMG_20181110_161246.jpg

IMG_20181110_152027.jpg

I haven't tried anything to solve this yet, I just wanted to share this right away and ask if anyone has seen this before?

[sandord]

Hmm, the desktop colour varies across resets between red, blue and grey. So every time I reset I get either the same colour or any of the other two. The end result seems to be completely random.

While running, nothing changes to this state so there's no flashing or any other distortion.

[sandord]

Mistery solved, I took the shifter out and put in another one (which is going to sit on my STF Remake board soon) et voila, a nice green desktop.

I cleaned the legs of the original shifter with IPA and put it back but that didn't help so my guess is that this shifter is broken.

[sandord]

The funny thing is that this particular ST is still usable in mono mode. Admitted, the right most 16 pixels are shown at the left of the screen but it's still workable. I might turn it into a MIDI machine or something ;-)

[troed]

Interesting. It's caused by a timing difference between MMU and Shifter - not really anything broken in it. What chip id is it on that Shifter?

[sandord]

Interesting. It's caused by a timing difference between MMU and Shifter - not really anything broken in it. What chip id is it on that Shifter?

That's probably true, broken chips are usually just dead chips.

The shifter reads:

CO25914-38A
PH23-024
8G5 23

I think it's interesting that a different shifter works just fine. Maybe it isn't the original one, the seller may have been swapping parts around.

[sandord]

I just realised that the problematic shifter might actually work fine in the STF Remake. I haven't finished building it yet so I won't know for a little while but if it does, I can put the other shifter on this new board and all will be fine :)

[Smonson]

For some unknown reason, this also happens to me with my FPGA shifter sometimes when there is no keyboard connected.