New Membrane Malfunction

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miked
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Re: New Membrane Malfunction

Postby miked » Fri Mar 10, 2017 4:41 pm

Thanks Tobias, while I've re-seated the chips I've not checked the ports or expansion bus, so that's something else I can try :)


RWAP
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Re: New Membrane Malfunction

Postby RWAP » Fri Mar 10, 2017 7:41 pm

Actually, in my experience, the most common cause of no working keys at all is..........

a) a tiny sliver of the old membrane left in the bottom of the molex connector (the molex connector is what you push the membrane tails into).
b) a dodgy molex connector. They tend to get bent over quite often and this can break the fragile pins, or the solder points on the underneath of the PCB. Also, is the membrane a tight fit in the two molex connectors? Some of the QL keyboard replacements used a small PCB which plugged into the molex connectors, forcing them apart and then the keyboard membrane is too thin to make a good contact (or even stay in the molex connector)!


miked
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Re: New Membrane Malfunction

Postby miked » Mon Mar 13, 2017 2:22 pm

Thanks for the info Rich. I've just plugged in a new 68008 and still the same. So that's a replace 68008, 8301 and 8049 and still not working, so time to check out the connectors based on your info :)

Cheers

Mike


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Cristian
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Re: New Membrane Malfunction

Postby Cristian » Wed Mar 15, 2017 9:55 pm

I'm experiencing some problems too. I've recently installed a new membrane and various keys often bounce/repeat. Sometimes CTRL and <- don't respond at the first push.
I can see no debris in the connectors.


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Dave
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Re: New Membrane Malfunction

Postby Dave » Wed Mar 15, 2017 10:10 pm

If this happens, often the bubble mat (the rubbery sheet) is just a little crooked. When you press the keys the bubble should make contact evenly on the membrane. If it is out of position ever 1mm or so, it will push down tilted and make contact, then straighten and make contact again. Depending on positioning this can cause a "bounce" or "miss" effect. The defining symptom is the problem nearly always happens to a key near the left or right edge of the keyboard.

Simple disassemble and reassemble the bubble mat and membrane and see if this helps. Enter the center screws first then the edge screws.

I've only seen a couple of bubble mats ever that have failed with small cracks. I don't know why or how that happened - they're probably the most durable QL part. When the dust of Earth-that-was is seeding other planets with life in 10 billion years, that life will be riding on a QL bubble mat.


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Re: New Membrane Malfunction

Postby RWAP » Thu Mar 16, 2017 7:41 am

You might also find that the bubble mat is too dry to the touch - I have seen ones where you can press down one of the bubbles and actually see it pop back up after a short delay...

I have lots of spare second hand bubble mats - but as Dave says, it is rare for them to fail - sometimes they need a good clean in a mild detergent and then rub them between your hands so that the oil from your skin adds a small amount of lubrication to the mat.


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Cristian
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Re: New Membrane Malfunction

Postby Cristian » Thu Mar 16, 2017 7:31 pm

RWAP wrote: I have seen ones where you can press down one of the bubbles and actually see it pop back up after a short delay...

This is not my case, fortunately.
Thank you very much Dave and Rich for your hints and suggestions :-)
I'll try soon.


miked
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Re: New Membrane Malfunction

Postby miked » Fri Mar 17, 2017 8:35 am

Based on the advice from the group I've checked the connectors and they are clear and tight fitting. I've also checked the continuity between the connectors and the 8049 and that is fine for all pins but still the same problem.

I've checked the board for other solder or track breaks and can't see anything. Having replaced the 68008, 8302 and 8049 and having checked the connectors and sockets such as the network sockets I'm lost now, not sure what to check next :cry:


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Dave
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Re: New Membrane Malfunction

Postby Dave » Fri Mar 17, 2017 7:57 pm

A little bit of alcohol across the contacts and the conductor side of the membrane with a cotton swab. Brief contact, air dry. Last thing to try then get a different QL and use this one for parts.


miked
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Re: New Membrane Malfunction

Postby miked » Sat Mar 18, 2017 4:17 pm

I agree Dave. While I hate to be beaten, I may need to look for another motherboard/QL :( and in the meantime get familiar with the schematic to see if I can work out enough of what should be happening to perform more checks. Going to need to up my kit with a simple logic analyser etc to see what is happening.



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