New CPC664 membrane but a few keys still stuck....

repetto74 · 15:30, 26 August 19

Hi guys,

I have replaced the CPC664 membrane with a fresh new one because the original one was bad and most of the keys were not working. Now the situation has drastically improved but I still have the 1,2 top row and Q,A,Z not working

. Those keys are all next to each other but I doubt this is a problem with the membrane otherwise many other keys would have failed (?).
Is it a problem with the coating on the rubber plungers? Or the membrane connector?
Any idea what can be done?
Thanks
Rick

Token · 15:45, 26 August 19

Try to clean again the connector. Maybe some fresh soldering could help. I hope that your new membrane have no problem. It could be the AY chip if you have still the problem.

Also beware with the membrane, even if it's a brain new one, working inside the 664 the less you can.

repetto74 · 17:30, 26 August 19

Is there any schematic available of the membrane connections so that I can figure out which track at the connector edge is concerned?
I have already applied fresh solder on the connector pins and the AY well I tested a with a joystick and it do respond. I can try to swap with another one anyway.

rambler · 19:37, 26 August 19

Edited 28. August:
Sorry for the bad link.
I see that you have solved the problem, but for references this is the right one:
http://www.cpcwiki.eu/forum/amstrad-cpc-hardware/cpc-664-coloured-membrane-tracks/

Maybe this post can help you:
http://www.cpcwiki.eu/forum/hardware-related/new-cpc664-membrane-but-a-few-keys-still-stuck/?action=post;last_msg=177599

repetto74 · 23:06, 26 August 19

Hi rambler,

The link you gave is the one of this thread

Bryce · 07:45, 27 August 19

Hi repetto,
1, 2, Q, A and Z are all on the same row connected to pin 11 of the keyboard connector. Try testing the CPC side first, ie: short pin 11 of the keyboard connector to pin 2 or 3. If a 1 or 2 appears on the screen, the membrane is the issue. If you can't get 1 or 2 to appear from shorting with a wire, the membrane has an issue.

Bryce.

repetto74 · 16:25, 27 August 19

Quote from: Bryce on 07:45, 27 August 19
Hi repetto,
1, 2, Q, A and Z are all on the same row connected to pin 11 of the keyboard connector. Try testing the CPC side first, ie: short pin 11 of the keyboard connector to pin 2 or 3. If a 1 or 2 appears on the screen, the membrane is the issue. If you can't get 1 or 2 to appear from shorting with a wire, the membrane has an issue.

Bryce.

Ok so I worked with the PCB turned solder side. The membrane connector has pins labelled from 1 to 19. Shorting pin 11 with pin 2 gives a "p" and with pin 3 gives a "i". Maybe the pinout is not correct? I am taking as a reference the pin number marked on the silkscreen.

Bryce · 07:05, 28 August 19

Maybe the board is labeled/numbered different to the schematic. Can you find any two pins that give you any of the characters the keyboard doesn't give?You should always be shorting between the two rows of pins, ie: don't short pins that are in the same row.

Bryce.

repetto74 · 09:59, 28 August 19

Quote from: Bryce on 07:05, 28 August 19
Maybe the board is labeled/numbered different to the schematic. Can you find any two pins that give you any of the characters the keyboard doesn't give?You should always be shorting between the two rows of pins, ie: don't short pins that are in the same row.

Bryce.

Hi Bryce,
Ok I will try all possible combinations of the matrix between the two rows and check.

repetto74 · 10:19, 28 August 19

Quote from: repetto74 on 09:59, 28 August 19

Hi Bryce,
Ok I will try all possible combinations of the matrix between the two rows and check.

I finally got "1" and "z" displayed with a pins combination so the PCB is working (pin 7 shorted with pin 14 and 16). Now problem may be at the edge connector with a bad contact. Looks weird to have a fresh new membrane defective. I will try shorting the pads on the membrane now.

Bryce · 10:28, 28 August 19

Be careful, the surface conductors on these new membranes are very easy to damage with scratches from wires/tools.

Bryce.

repetto74 · 10:57, 28 August 19

Quote from: Bryce on 10:28, 28 August 19
Be careful, the surface conductors on these new membranes are very easy to damage with scratches from wires/tools.

Bryce.

Bryce I found where the problem is. If you look at the square cut bottom right you will see that the corner has slightly sheared and cut the track

. I have some conductive coating I can apply to fix this area. Anyway this membrane looks too fragile for a supposed new product.

Bryce · 11:19, 28 August 19

Didn't you just buy this from RWAP?? Send it back, he owes you a working one. With the rip it will not be a robust fix and fail again almost immediately.

Bryce.

repetto74 · 11:24, 28 August 19

Quote from: Bryce on 11:19, 28 August 19
Didn't you just buy this from RWAP?? Send it back, he owes you a working one. With the rip it will not be a robust fix and fail again almost immediately.

Bryce.

Yes it is from RWAP. I will get in touch with them and sort this out in case. The coating is quiet robust when dried and this area is supposed to stay flat without bending or whatsoever. I 'll try.

repetto74 · 13:44, 28 August 19

I have applied a fat blob of conductive paint and let it dry under the sun. Checked the continuity ok now and have re-seated the membrane carefully into the keyboard. Finally I have a fully working keyboard

. I am not using this CPC664 a lot, it is more part of my collection and will seat on the shelf. I need anyway to dig out a 12v PSU for the DD and a 3" disk to test it definitely (rare to find those 3" diskettes). This project was lasting for a long time now so glad it comes to an end.

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New CPC664 membrane but a few keys still stuck....