Need help: How to fix screen color problem of TurboR A1GT?

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By l_oliveira

Hero (533)

l_oliveira's picture

24-02-2015, 13:19

Actually the *only* difference is that on A1ST the *CSYNC* (composite sync) became *CVBS* on the A1GT. Some monitors *loathe* CVBS on their sync input and will glitch.

CVBS = Composite Video Baseband Signal, aka "yellow plug"

By anonymous

incognito ergo sum (116)

anonymous's picture

25-02-2015, 15:12

Quote:

Actually the *only* difference is that on A1ST the *CSYNC* (composite sync) became *CVBS* on the A1GT. Some monitors *loathe* CVBS on their sync input and will glitch.

And that's exactly my situation. My monitor is a Sharp CU-14FA from a X68000 system. It has a Japanese 21-pin RGB connector (same plug as SCART, but different signals). This display works beautifully with my A1ST, but goes crazy with my A1GT when there are whites on the screen:



(not an artifact of the camera, this is what the display looks like to the human eye)

Any ideas on how to solve this?

By l_oliveira

Hero (533)

l_oliveira's picture

25-02-2015, 15:31

There's a jumper inside the computer you can toggle, it will disable the CVBS and make it into CSYNC.

But it's a soldered wire bridge. You need to dismantle the computer completely and swap the wire bridge from the CVBS position to CSYNC position using a soldering iron and a solder suction pump.

By anonymous

incognito ergo sum (116)

anonymous's picture

25-02-2015, 15:36

l_oliveira wrote:

There's a jumper inside the computer you can toggle, it will disable the CVBS and make it into CSYNC.

But it's a soldered wire bridge. You need to dismantle the computer completely and swap the wire bridge from the CVBS position to CSYNC position using a soldering iron and a solder suction pump.

Oh, that'll be great. Do you happen to know what jumper it is?

By l_oliveira

Hero (533)

l_oliveira's picture

25-02-2015, 16:35

J1 and J2 near the A/V connector on mainboard. I think you need to cut the trace in the original one and jumper the other to change. I thought it was a wire bridge but it's a trace with a cutting place in the middle. You cut the closed one and put solder on the open one.

To change back to original position you remove the solder from the other and place solder on the original to close it again.

By anonymous

incognito ergo sum (116)

anonymous's picture

25-02-2015, 16:38

Thanks! I'll try it this weekend and let you know how it goes.

By anonymous

incognito ergo sum (116)

anonymous's picture

25-02-2015, 16:50

These two, right?

Do you think they'll be bridged on the back of the board as well?

By anonymous

incognito ergo sum (116)

anonymous's picture

25-02-2015, 17:04

Never mind, I just checked. In the back of the board these jumpers are connected to a couple of resistors.

By anonymous

incognito ergo sum (116)

anonymous's picture

25-02-2015, 17:45

I didn't want to keep using the crappy HDMI upscaler, so I went ahead and I did the modification now. I cut the J2 trace and bridged J1 with a drop of solder.

It works flawlessly. Thanks SO MUCH!

By l_oliveira

Hero (533)

l_oliveira's picture

25-02-2015, 17:47

JaviLM wrote:

I didn't want to keep using the crappy HDMI upscaler, so I went ahead and I did the modification now. I cut the J2 trace and bridged J1 with a drop of solder.

It works flawlessly. Thanks SO MUCH!

Glad I could help. :)

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