Fixing Expert HD video board, need advice.

[Zom]

Hello all, first post here - I'm happy to see that there's a somewhat in-depth English forum section devoted to this wonderful machine.

To my question:
I have an Expert with a damaged video-board - apparently it was damaged by using a VGA adaptor hooked to a "semi-modern" LCD monitor (not TV).
The previous owner told me he just hooked it up on that LCD, didn't work, plugged it in the Sharp's original monitor again and now the machine just shows garbage.
All I get now is a completely out of sync picture. Does anyone know more about this? I'm good with soldering and took a look at the Expert's "detachable" video-card; the resistors seem to be ok...
As for everything else, before I start replacing every single cap on that board, does anyone know something about this? A little hint on what could be fried or where to start?

Thanks in advance.


P.S. forgot to add that 15kHz signals seem to sync properly horizontally, but they're vertically out of sync. Everything else just skips diagonally.

[eidis]

Hi !

If he connected the LCD monitor while both devices were powered on, it could be that your Expert got a proper dose of static electricity. Fortunately most of the times all that is needed to fix such old hardware is replacement of all system critical capacitors. My ACE was behaving strangely and new capacitors brought it back to life, including one floppy drive. Give it a try and please post your results. You could try removing the CMOS battery and resetting the SRAM. If that won't help, it could be a fried motherboard.

Eidis

[eidis]

 I have another idea. Check it out:

http://www.hardwarebook.info/X68000_A/V

Make sure that Ground, H-Sync and V-Sync signal from your Expert is getting to your display device. Try connecting H-Sync and V-Sync lines together to make Composite Sync and see if anything changes. It could be that something has happened to one of your Sync lines. If you have a TV with RGB Scart input, you could try to make an adapter and test 15khz modes. I once did that and can confirm that X68000 displays picture on a regular TV in 15khz mode. Then again, I used a TV from the last century.

Eidis

[Zom]

If he connected the LCD monitor while both devices were powered on, it could be that your Expert got a proper dose of static electricity

Didn't know this happens so easily...

Anyways, resetting sram  didn't help (as expected). I guess the boring cap-replacing season begins... there are a lot of them, so I will start with the video board first. If nothing goes then the mainboard will be next.

Try connecting H-Sync and V-Sync lines together to make Composite Sync and see if anything changes

Will try that out, I have plenty of old CRT tvs lying around. but I somehow doubt that changes anything...
Also, I tried measuring the RGB lines and strangely enough I didn't get anywhere near 0.7 volts. ? more like 0.1, seems they're busted too?

Anyways, thanks for the info!
I will post my findings once I've at least "refreshed" the RGB board.