New Membrane Malfunction

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kordics
ROM Dongle
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New Membrane Malfunction

Postby kordics » Mon Apr 18, 2016 1:05 pm

Hi Everyone!

Today I have received a long waited shipment from UK: Intel 8049 coprocessor & a new keyboard membrane. My QL was not operational since 1987, and ever since I wanted it to repair. So, I replaced the 8049 and keyboard membrane, but still QL doesn't work.

Before 8049 the replacement I couldn't reach F1 monitor & F2 TV selection. After the replacement F1 & F2 selection screen appears. I guess that means that everything with 8049 is OK. Now, when I try to press anything, including F1 & F2, on the keyboard with the new membrane nothing happens.

I guess the problem is in the new membrane, or something else could be malfunctioning as well? I would appreciate if you can share your experience about new membrane replacement.

Kind regards,
Stevan Kordić
Radanovići, Kotor, Montenegro


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Re: New Membrane Malfunction

Postby RWAP » Mon Apr 18, 2016 7:22 pm

Hi Stevan,

It could indeed be an issue with the new membrane, but the failure rate on these QL membranes is extremely low (maybe 1 in 125).

The first thing to do is check that you have not left any bits of plastic from the old membrane in the two molex connectors (where the membrane tails go). This is the most common reason for a new membrane not appearing to work! Use a torch and pair of tweezers to remove any small bits.

If that works, then try the molex connectors - you can use a thin piece of wire to connect each pin in the 9 way connector with each pin in the 11 way connector - that replicates the membrane.

According to the martix diagram - http://www.deblauweschicht.nl/tinkering/qlkeys1.html - you need to connect pin 1 on the 9 way with pin 3 on the 11 way connector.


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kordics
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Re: New Membrane Malfunction

Postby kordics » Mon Apr 18, 2016 8:32 pm

Hi Rich!

Thank you very much for the advices about membrane malfunction. I will check if there is some obstacle in the molex connectors and I will try to directly connect the pins, according to the diagram you provided. I will report the outcome...

Kind regards,
Stevan


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Dave
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Re: New Membrane Malfunction

Postby Dave » Thu Apr 21, 2016 6:15 am

The second most common user problem with membranes is when the user installs them so the second insulating layer covers the first conducting layer.

Of the two layers, only the layer with the metallic striped should be inserted into the connector. If both are inserted the board will not work.

This was the commonest cause of replacement membrane issues at Sandy.


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kordics
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Re: New Membrane Malfunction

Postby kordics » Sat Apr 23, 2016 7:20 pm

Dave,

Thanks for the suggestion! My membrana contacts are exposed, without insulating layer over them. My problem is either membrana, ether the rest of the QL.

Kind regards,
Stevan


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Re: New Membrane Malfunction

Postby RWAP » Sat Apr 23, 2016 7:31 pm

Did you check for any bits of the old membrane inside the connectors - or try the wire to connect the pins for F1/F2 ?


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kordics
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Re: New Membrane Malfunction

Postby kordics » Sun Apr 24, 2016 10:02 pm

Rich,

The connectors are clear inside. Connectors are not the cause of the problem. I did try to connect pins for F1/F2, but without success! Ether I was connecting wrong pins, ether there is something else wrong with my QL. I have tried to connect pin 1 on the 9 way with pin 3 on the 11 way connector, if we count them from the left to right and the QL is in the normal position in front of us. Connecting them made no effect. On TV still there was F1/F2 initial screen. If I did right pin connection, then something else is also wrong...

Kind regards,
Stevan


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Re: New Membrane Malfunction

Postby RWAP » Mon Apr 25, 2016 8:38 am

Hmm - it sounds as though the molex connectors might be at fault - try connecting pin 1 to pin 4 (which should be F2).

You may need to check the underneath of the motherboard where the molex connectors are soldered in..

Did you purchase that membrane from me? If so, pm me your details and I can send you a replacement membrane once I have some more in stock....


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Re: New Membrane Malfunction

Postby miked » Fri Mar 10, 2017 3:56 pm

Did this particular issue get resolved?

I have a QL in which I've tried two new membranes and I get no keyboard input at all. I've replaced the 8049 and 8302 and still get no keyboard input. The machine does give me the start F1/F2 start screen, so it would seem the CPU and ROM are OK. That said, the service manual says to replace IC18 which is the CPU if the keyboard continues to not work. I have a new CPU on order just in case that is the problem.

My problem sounds just like the original posters issue hence checking if it was every resolved :D

Mike


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tofro
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Re: New Membrane Malfunction

Postby tofro » Fri Mar 10, 2017 4:31 pm

I have had one QL in the past where a defective network connector completely confused the 8302. Those connectors should make contact when the plug is removed and sometimes don't when corrosion is involved. A confused 8302 can lead to a confused 8049 and thus a non-working keyboard.

Otherwise, removing and re-seating all sockeded chips normally doesn't hurt.

Annother common source of hardware malfunction are bent pins in the expansion port that create shorts.

Obvious cases like wrongly inserted chips I'm not considering here - I guess you checked that already.

Tobias



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