Keyboard Problems

rune · July 2013

Hi, I need a bit more help...

I tested the Spectrum + I got from ebay today and there seems to be a problem with the keyboard.

It looks like the middle 4 keys on each row are not working (4567 rtyu fghj cvbn).

Does this indicate a problem with the membrane or hardware?

Are there any tests I can do or areas to check - I dont want to make things worse by fixing it until its more broken than it is already.

If its the membrane, where is the best place to get a replacement? I guess it has to be a Spectrum + specific membrane.

rwap · July 2013

It definitely sounds like a problem with the membrane - check that all screws are in the back of the keyboard plate and the two clamps which go across the membrane tails are tightened correctly (DO NOT OVERTIGHTEN THOUGH AS YOU MAY BREAK THE SCREW PILLARS)

Best place for a membrane ? www.sellmyretro.com (I sell them) - and yes, you will need a Spectrum+ specific membrane

rune · July 2013

Thanks Rich

I've removed and reinserted the membrane into the motherboard and now its just the middle two keys that dont work.

The widest socket seems to move a little front to back and I thought it had split, but that may just be my eyes.

I'll try the backing plate and if that doesnt work you may have a new customer :)

Dave

rune · July 2013

Looking at a membrane replacement on You Tube, there were 2 backing plates on the guys Spectrum+ - A black and a white one.

Mine only has the white backing plate. Were some Spectrums made like this or are there parts missing? If missing, does the black plate matter?

gtsamour · July 2013

Yes there were Spectrums with white plastic backplate and others with metalic.

rune · July 2013

A bit more googling and I got a tutorial showing only the white plastic back plate so mine seems OK.

I cannot see any cracks or breaks looking at the membrane with a strong backlight.

Tonight check coninuity on the tracks and check for dry solder joints on the ribbon socket as it seems only to affect keys on the "5 way" connector".

rwap · July 2013

Yes, it could well be the soldering on the molex connector - you can always check these by using a small wire to connect each pin on the 8 pin connector to each pin on the 5 pin connector...

rune · July 2013

Well, I could get all charachters by using a bit of wire and connecting the molexs, so it looks like the membrane is a gonner.

New one ordered from Rich.

u6c87 · July 2013

rune wrote: »

I've removed and reinserted the membrane into the motherboard and now its just the middle two keys that dont work.

The widest socket seems to move a little front to back and I thought it had split, but that may just be my eyes.

I'm intrigued that reseating the connector brought some keys back. It may be that either the pins of the molex connectors are snapped (that was my problem from back in the 90s) and a bit of movement partly made the connection again, or possibly that the springs in the connector need "retensioning". I suppose the ends of the membrane are also a bit worn or dirty, but a replacement membrane will sort that out.

Last year I ordered both a membrane and molex connectors from RWAP (to replace the horrible butchery job I did back in the mid 90s) and now I have a nicely working rubber key 48K :D

rune wrote: »

Well, I could get all charachters by using a bit of wire and connecting the molexs, so it looks like the membrane is a gonner.

It could still be the molex connectors at fault - a wire is quite wide in comparison with the membrane connectors, and you'll move it around until it makes contact, whereas the membrane won't. It may be that you need the molex connectors too.

Macc · July 2013

Ive found that on the more hard wearing membranes sometimes found in the plus that a bit of cartridge cleaning fluid or even isopropyl can restore them, just clean the ends as best you can. With this connector cleaning cream I have here ive had them gleaming, usually work after that

rune · July 2013

Wish I'd thought about the ISO before I ordered the new membrane.

The fact that I can get the keys using wire is encouraging. For me that makes the fault in either the molex or membrane so it should be fixable even for someone like myself.

Strangely, it was the 8 way molex that seemed to wiggle the most. But the (D3 and) D4 connectors in the 5 way that was the problem.

Will post how I get on when the new membrane arrives.

DEATH · July 2013

Careful using IPA on the ribbon connector traces, it can dissolve the conductive silver off pretty quickly.

Spectrum+ keyboards have a design fault - same for the 128 toast rack. Notice the clamps that are holding the membrane in place? There are two of them. Quite often the larger of the two goes a bit slack, and even though the screws are tight, contact is lost. Clean the conductive surface area that fits under the clamp and try a thin bit of card as a packer to make sure it's compressed really well. Be VERY careful, as I said, IPA can remove those silver traces if you're careless. If you notice it getting tacky whilst you're cleaning it, stop and let it dry off properly before trying again.

To be honest, if you have a new one on order, I guess you have nothing to lose, do ya :)

rune · July 2013

I'd like to say a big thank you to everyone who took the trouble to reply to my post. My new membrane arrived today (thanks Rich) and I now have a fully working keyboard. :D

I spent a little while reaquainting myself with the joys of a "real keyboard".

Now I need to sort out some way to load programs without a tape. Got an amplifier in the shed and an MP3 player and some micro SD cards... But thats for another thread ;)

First I need to see if there's a Spectrum + manual somewhere and work out what key combinations are needed to get the keywords.

Macc · July 2013

Heres a link to the manual

Keyboard Problems

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