STE video chip

[exxos]

As a update. I tested 3 motherboards with 1712 shifter. These boards are the integrated blitter types with 001A DMA. A quick test and they all give the diagonal pattern and I don't see any issues from power up.

My other boards are external blitter types but have the original 588 shifter. So I didn't bother to test (machines in a bit of a state anyway)

I would have concluded the 1712 shifter is simply not compatible with the integrated blitter GST. This seems to be the trend currently. But @Steve's STE had the graphics problem with 588 shifter by the looks of it ? So maybe we should be documenting GST numbers at this point..

EDIT:

Its not a big enough sample set to draw any conclusions.but....

Looks like:

588 shifter is paired with 1989 batch GST (external blitter).
1712 shifter is paired with 1990 batch GST (external blitter)
1712 shifter is paired with 1991 blitter GST (integrated blitter)

I can't imagine batch codes being the problem, but something has changed causing the problems. I can only assume at this point, the 1712 shifter is not compatible with the 1989 batch GST. I don't have enough boards or test results to make any more headway with this problem.

But my tests do show some issues swapping the shifters. I'd assume the 588 shifter would work fine in any board, but the 1712 would not. Then the dumb-luck factor if a board has the problem or not, like it normally is!

[Steve]

I'll open up my STe's tomorrow to remind myself which one I installed the little board in. I vaguely remembering installing it in both at one point.

[exxos]

I'll open up my STe's tomorrow to remind myself which one I installed the little board in. I vaguely remembering installing it in both at one point.

Thanks. If yours doesn't fit my proposed theory, then its likely a borderline timing issue with something again. I guess different batches of chips could effect things just enough to make or break things, if they are "on the edge" already.

[exxos]

:roll:

Capture.PNG

Ain't going though JLC part souchong nightmare again. So will have to get shelved again unless there's a flood of people appearing with the same problem to warrant all the hassle of getting them made.

I do still have 5 of the prototype boards left anyway..

[Steve]

@exxos I just checked and I have the little board fitted in my 588 STe but not my 1712 STe (Although I did try it in the 1712, but removed it as it wasn't required)

For me it was for fixing blitter heavy demos. I never had the strange video output corruption you demonstrate. But it worked for fixing my blitter issues.

ps - I noticed, mine have the variable pot, but I never touched it. I assume it was set correctly to begin with from you?

[exxos]

@exxos I just checked and I have the little board fitted in my 588 STe but not my 1712 STe (Although I did try it in the 1712, but removed it as it wasn't required)

For me it was for fixing blitter heavy demos. I never had the strange video output corruption you demonstrate. But it worked for fixing my blitter issues.

ps - I noticed, mine have the variable pot, but I never touched it. I assume it was set correctly to begin with from you?

Hmmm did your problem STE have P100 as 1.2k ?

[Steve]

yeah both do.

[exxos]

yeah both do.

It's a odd one.I have had the odd blitter behave oddly but never looked into it. But not sure how the shifter 16mhz sync would get effected by the blitter :shrug:

[exxos]

I tried @ijor's blitter test program here viewtopic.php?f=25&t=6040 But I can't seem to get the more corrupted background lines on this machine now. But I can corrupt the video to give the same video faults. So there could be 2 problems in the mix of all this.

IMG_1602.JPG

IMG_1603.JPG

IMG_1604.JPG

IMG_1605.JPG

So I think other than looking at the video visually there does not seem to be any reliable method for detecting such glitches easily :(

[exxos]

Found 2 other STEs with 588 shifter. Though swapping to the 1712 shifter doesn't yield the expected results and both seem fine :roll:

IMG_1606.JPG

IMG_1607.JPG

I even tried heating up the GST but nothing changed.

So the sort of conclusion so far is that the 1712 shifter may not work in some early machines depending on the alignment of the planets etc