Good morning.
Let me introduce myself, my name is Lorenzo and I am a new member.
I am passionate about electronics and computers in general and for some time now I have been playing with both modern and vintage computers, but also with console emulators and emulators of various types of computers.
I recently bought a Philips MSX computer, model VG8020/20, at a flea market. It was quite damaged but at least partially functional.
The fact is that the machine starts up normally, displays the basic screen, but then automatically starts writing a series of random letters without sense, as if random commands were being given to it from the keyboard, but without me typing anything.
Furthermore, as the title suggests, the message syntax error appears repeatedly.
I have already done a series of tests. By disconnecting the two flats of the keyboard the problem disappears. Reconnecting it returns. I tested the two membranes of the keyboard with the multimeter to see the continuity and apparently all the carbon contacts seem connected. Finally I cleaned all the membranes and the entire keyboard with isopropyl alcohol, but the problem persists.
At this point I ask a forum of specialists, maybe someone understands how to solve the problem.
I'm attaching a screen for now. If you know how to attach more and maybe even some videos I'll attach those too.
Thank you for your availability.
Lorenzo
Hi Lorenzo,
well, welcome, I know the 8020, I've always had it. Its problem is that in the flats of the keyboard on the horizontal lines of the upper and lower membrane matrix there is a short circuit where the keys that give the result of pressing .moqt and RETURN are located. It would be necessary to investigate better the coupling and isolation of the 2 membranes. Without neglecting also a check of the main lines of the .moqt and RETURN crossings from the membranes, motherboard tracks, towards the 8255 chip.
try to see a diagram here, it's not a Philips 8020 but the diagrams are the same:
https://www.leadedsolder.com/2021/09/07/casio-pv7-power-jack-keyboard-repair.html
let us know
HI
TO.
Good evening.
Sorry, unfortunately I'm not a technician, could you repeat it in a simpler way?
In practice, according to you, there would be a short circuit on the flat cable that causes a false input of the .moqt and return commands?
But how do I figure out which keys these are? Is there a diagram?
In the meantime, I wanted to investigate further and I want to send you this photo that I took under the microscope.
This is a photo of the flat cable of the upper membrane of the keyboard (with the larger flat).
I don't know much about this, but from what I see it looks like the graphite tracks are completely missing. Is that correct?
How do I solve it?
Thank you.
It looks badly damaged. I tried to measure continuity with the tester and it seems to be there, except for one track.
I tested all the tracks, placing one of the two probes right in the spot where the graphite seems to have gone away to see the continuity.