MegaSTE Repair Continued - Video Noise

[geogeo_28]

New picture of the noise:

IMG_0409.jpeg (306.67 KiB) Viewed 4468 times

[exxos]

Well, whaddya know...
Wired up a Meanwell RQ85B, and here's the output (earth connected, OSSC powered via its usual USB adapter).

BTW if that PSU is better, have you tried moving it closer to the motherboard ? Also wondering if the video is picking up interference from the PSU.. and as you have the meanwell "out" of the way... was just a thought anyway..

[exxos]

Also the problem may be on the RGB drivers .... May need better caps...

Capture.PNG (128.52 KiB) Viewed 4427 times

[geogeo_28]

I replaced all the caps with new ones but I should definitely test them again. I have an Atlas ESR70 to help. I have to check the diodes also.
Is it possible that the floppy controller adds noise on the bus? Definitively, I know that I have issue with this controller and it needs to be replaced.

[exxos]

The whole motherboard is a noise generator..

[geogeo_28]

Unfortunately, switching to another shifter did not solve the problem.
The motherboard has a bigger issue... Keep you posted if I make progress..

[displaced]

BTW if that PSU is better, have you tried moving it closer to the motherboard ? Also wondering if the video is picking up interference from the PSU.. and as you have the meanwell "out" of the way... was just a thought anyway..

I didn’t try this I’m afraid - got caught up in other stuff. But in the meantime, I received one of your recap kits for the MSTE PSU and fitted it. There’s slightly more noise than with the Meanwell, but not enough to be a problem. Could be, as you say, proximity related. Still well within what I get with my other old machines, so I’m happy with it.

Got an Epson SMD-340 on the way to go with the AJAX and HD-capable GAL in the machine. Then I just need to wait for the weather to warm up so I can respray the case.

[geogeo_28]

@exxos Sorry to revive this topic. By curiosity I saw a post https://www.atari-forum.com/viewtopic.php?t=27647 where you mentioned the possibility to create a buffer for the RGB lines to clean the signal.
Do you have a schematic or could you give more details about this circuit?
Thanks a lot!

[exxos]

@exxos Sorry to revive this topic. By curiosity I saw a post https://www.atari-forum.com/viewtopic.php?t=27647 where you mentioned the possibility to create a buffer for the RGB lines to clean the signal.
Do you have a schematic or could you give more details about this circuit?
Thanks a lot!

The project was abandoned a long time ago.. too much noise on the motherboard, and even if you buffer everything and make everything look perfectly fine on the scope, the route across the motherboard will pick up noise anyway. If you want better video you will have to wait for the next batch of H5 motherboards where all these problems have been fixed.

[geogeo_28]

I guess I will wait for the next batch of H5 motherboards.