Weird keyboard issue

Master (202)

02-01-2023, 22:35

I'm experiencing a very strange issue with the keyboard of my AX-370. To start, the machine is very clean, and each of the keyboard buttons work great when tested individually. However, certain combos stopped working properly. For example, holding left+up arrows works but if you also press the space bar, then left no more works until you release the space bar.

At first I thought some dirt went into the keyboard, so I opened the machine and disassembled the keyboard and cleaned it then put everything back together. Now all keys work great again even with combos without issues. The keyboard was already clean though.

I left the computer a few days, then used it again and noticed the problem came back! This time I only disassembled the keyboard and put it back together, and it worked great again. So I decided to keep watch on the machine. I left it lightly screwed to rule out any possibility I'm over-tightening the screws and causing some trouble in the keyboard. After playing daily with the machine, on day 4 I noticed the issue creeping back slowly. Only a few combos stopped working but not yet as bad as it got before. I believe given more time the rest of the combos will stop working too.

I'm puzzled by this problem. Because even when the issue is happening, still each button works great individually! Only the combinations stop working.

How could this even happen? How electrically it's possible to get only combos to stop working after a few days of re-assembling the keyboard. It has to be a physical issue that gets temporarily fixed by disassembly/reassembly. But I can't imagine what it could really be. The keyboard ribbon cables look good to me, and I guess if they were damaged, keys would not work period.. not just combos.

Any ideas?
Cheers, and happy new year!

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By sdsnatcher73

Enlighted (4289)

03-01-2023, 04:12

Happy new year to you too.

Try putting a layer of paper (I used regular A4 80gram cut down to size) between the membrane and the metal cover. This has fixed issues in some machines that had “weird keyboard issues”. I suspect the plastic insulation in the membrane itself changes somehow over time and does not work as well anymore. This causes leaks of current to ground (the metal plate). Depending on how bad it is the situation will differ I reckon.

On one machine the keyboard was fine with the machine open, than started typing randomly (but consistently the same combination) when the machine was closed), this was a PHC-70FD

By wbahnassi

Master (202)

03-01-2023, 17:25

Hmmm.. How does this membrane technology even work? It's two thin plastic sheets with traces embedded in each side. I assume the pressure of the key is making the two plastic sheets press against each other and a contact is thus made on that location?

If so, what prevents the keys from randomly making contact? I mean there is very thin space between the two sheets so it's possible that the two sides touch each other at several locations. Yet obviously this doesn't happen. In fact it's quite precise, and a keypress doesn't (for example) cause the keys around it to press too.

Now following your suggestion sdsnatcher73, I've tried putting a sheet of food wrap actually. I thought it will prevent shorts yet it's very thin to not cause additional thickness that would wear the plastic clips that hold the keyboard to the metal plate. (gosh I'm always afraid those would break one day, and then the keyboard would be dead).

Here are photos with the food wrap added. I will need to test this across the week to see if the problem will manifest again or if this is enough...

Thanks! :)

By wbahnassi

Master (202)

09-01-2023, 23:31

So back again with the same problem. But I think now I might now know what could be wrong. I read about this membrane mechanism and it seems the typical (modern) ones are made of three sheets of plastic: the top and bottom ones have traces printed on them with conductive ink. Then a middle sheet is placed in-between to guard contact between the two sheets from ever happening except at allowed areas.

Now this AX-370 keyboard membrane is actually 2 sheets only. No middle protective sheet in-between. Instead, the traces from one of the sheets are covered with a sticky substance that's acting both as insulator and glue. I am suspecting that this substance is getting squished out and causing some contact to happen on the traces, which is causing the issues. The solution is probably to detach the two sheets off each other, and add a protective sheet that I do myself (paper or plastic). But I'm afraid I might mess things up if I detach the sheets from each other, as they are glued all around the edges. Detaching them would involve some force and I'm not sure the thin plastic will endure it.

I guess I could ask if someone has a membrane like this for parts. Or if there is some service that can make them if we give them a design?

Cheers!

By sdsnatcher73

Enlighted (4289)

15-01-2023, 15:29

There was a firm in Spain who made the HB20P membrane, maybe get in touch with them?

By wbahnassi

Master (202)

15-01-2023, 17:49

Thanks, I don't know this firm. Do they have an email or website?

By sdsnatcher73

Enlighted (4289)