VG8000 keyboard matrix lines missing

By Wlcracks

Expert (85)

Wlcracks's picture

17-05-2017, 14:18

I am restoring a defective VG8000, it had a mayor short in the i/o slot.
Replaced the ROM IC663 with an eprom, because the computer wasn't booting. Worked again.
Replaced TS359 because the cvbs output was flaky. Worked again.
Replaced IC702 and IC703 because the joystick was acting up. Not sure if these were the cause.
I removed IC676 waiting for replacement, i did had one in stock, this should be an problem this is the output buffer to the joysticks. Joystick seems to work fine now.
Done all this, and now some lines of my keyboard don't work anymore. It did work fine.
My first idea was the traces were gone from inserting while restoring the flexcable "connector". When i measure with an scoop on IC698 i see the defective lines pulses dropping not to zero but about 2.5V. The working lines near zero. When shorting directly e.g. spacebar this works.
I cut a 4mm of the flexcable but that didn't do a difference. Still not al key working and defective signals show same.
The keyboard has been molded down and is a bitch to disassemble and assemble again.

Anybody experiences or ideas to share?
Thanks!

Login or register to post comments

By Wlcracks

Expert (85)

Wlcracks's picture

17-05-2017, 14:29

and yes i checked for ransomware.

By Wlcracks

Expert (85)

Wlcracks's picture

18-05-2017, 20:14

Could not find any problems so, i cut the flex cable of the keyboard another 4 mm. Solved. Fixed!
Thanks!

My MSX profile