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 Post subject: UMSA sync issue
PostPosted: Mon Mar 23, 2020 7:53 pm 


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Joined: 09 Apr 2014
Posts: 296
Location: UK
Hello, I've had a UMSA for a while now but only recently started using it. It's been fine for about 2 weeks but the other day I no longer get a stable picture:
Image
I'm assuming it's a sync issue as the colours look correct the odd time you see a semi-coherent image pass and it's switching to AV okay.

I'm not savvy at all with a multimeter but tested what I could with the help of a friend:
Image
VGA cable checked to see if it's working by outputting directly to a PC CRT
Swapped out the Male to Male SCART cable to the TV (same result)
Checked the TV's SCART socket is still working (TV accepting SCART input directly from a console)
Check to see if the Sync out/Pin 19 on the SCART is alive. A 0.77 voltage reading with a MM was read (I think you need an oscilloscope to really confirm if this is okay?)
Swapped the Neg/Pos jumper (no change)
Used another 15khz RGBHV source into the UMSA (no change)
Pin checks done on the sync in/outs where they're soldered on to the PCB (seemed okay)

I read you can't really check caps on a circuit so those are still questionable and the other tests probably don't really prove those parts aren't faulty either. I'm wondering what people here would do next?

I did come across this thread on Arcadecontrols where the OP has a similar issue (but assumes, correctly?) it's his TV
Image

I checked the H+V sync pins were soldered okay to the PCB because of a forum poster in the same thread who said this (although I'm not sure what he's on about):
Quote:
hi did you solve the proplem? coz i have the same issue i recived my umsa few days ago it was working fine but now its not
I think my umsa problem is from the vga input somthing wrong with the pin coz when i touch the second pin in the back of umsa the image look ok , i took the umsa to eletronic shop to remove the vga inpunt and replace it with new one i will wait and see


It's a dead thread but I did PM them regardless to see if they ever solved the problem.


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