Skipping video

[PeckPeekPoke]

Hello,
I have a naughty 1040STf with video that is jumping; the picture keeps rolling off the screen. I just completed a recapping, and replacement of the pullup resistors yet still have the same problem. Where should I look now?

[exxos]

It might be your monitor ? ST video isn't "ideal". If you monitor has V-Hold present then tweak that.

[PhilC]

What screen are you using?

Is it vertical or horizontal rolling, is the rest of the picture fine?

It may be that your hsync or vsync have a bad connection.

Hsync and vsync can be traced straight from the glue to get monitor socket, so a real quick check could be to remove the glue, clean and straighten any pins and then see if that fixes it.

[PeckPeekPoke]

It might be your monitor ? ST video isn't "ideal". If you monitor has V-Hold present then tweak that.

For video, I use an upscaler board into a VGA which seems to work well with my other ST's monitor output. That other machine, yet to be re-capped, also begins skipping, but after 15-20 minutes of use.
Perhaps it is my upscaler and monitor but I doubt it since I've used two monitors, and my 2nd machine is an stfm which behaves the same with a television.

So I removed my Shifter, deoxed it and the connectors, and found continuity between IC pins 2,20, & 21 and monitor #12 (vsync). replaced the Shifter and now I've got the White Screen of Death. Though I've got your diagnostic cartridge, I'll have to wait for a null modem cable to get here.

[PeckPeekPoke]

It may be that your hsync or vsync have a bad connection.

Hsync and vsync can be traced straight from the glue to get monitor socket, so a real quick check could be to remove the glue, clean and straighten any pins and then see if that fixes it.

I couldn't find continuity to Hsync, but perhaps I had the wrong pin on the monitor out. Still exploring that avenue. Things have gotten worse since I reseated the chip, so maybe a trace or joint. I wish I had schematic for this 70523 board.

[PhilC]

@PeckPeekPoke with regard to the GLUE, MMU and Monitor Socket you can use any ST schematic as the pin layouts are the same.

As a for instance Vsync & Hsync are on pins 37 and 38 on the GLUE and go to 12 for vsync and 9 for sync on the 13 pin monitor socket.