Fixing keyboard mylar sheet/keys

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rubber_jonnie
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Re: Fixing keyboard mylar sheet/keys

Post by rubber_jonnie »

@Pacman I was slightly worried about the resistive properties, but it was such a short gap it was no problem in the end.

The kapton tape is so similar to the original top layer of mylar it seemed logical to both protect the carbon ink and provide an insulating layer. It's been fine for me for ages now:)
Collector of many retro things!
800XL and 65XE both with Ultimate1MB,VBXL/XE & PokeyMax, SIDE3, SDrive Max, 2x 1010 cassette, 2x 1050 one with Happy mod, 3x 2600 Jr, 7800 and Lynx II
Approx 20 STs, including a 520 STM, 520 STFMs, 3x Mega ST, MSTE & 2x 32 Mhz boosted STEs
Plus the rest, totalling around 50 machines including a QL, 3x BBC Model B, Electron, Spectrums, ZX81 etc...
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Re: Fixing keyboard mylar sheet/keys

Post by Pacman »

That carbon pen sounds like a good product, and I need to get myself one myself :)

Being outside of the UK the challenge is finding a plce to buy it without it costing too much with all the import duties and stuff.
I see that it's available from several of the big electronic component dealers, so once I find the time to make a up a list of components I need (I have a few "to do" projects layound around) I'll see about including it in one of those as it's more predictable to figure out the final costs (they often include all import duties) as opposed to buying from eBay or what have you even though you have to make up a sizeable order before to make it worthwhile. May I ask where you got your conductive carbon pencil from?

I'll have to include kaption tape in that order as well. Seems like a good and important precaution to take once you've fixed a PCB trace.

I don't know what's causing the contact problem with the "Help" key: if it's the rubbery part on the key itself or the black pads underneath it on the mylar sheet, but once I get the "Keypad fix" I ordered and apply it to the rubbery part I might as well apply a thin layer of "Wire glue" with a brush to the black carbon pads on the mylar sheet as well -sounds like a good idea?
You had a good suggestion in another thread to magnify the areas in question first to see if it's worn out or not, prior to actually applying any new carbon based conductive layer of some sort.
I don't want to pry open/close the keyboard assembly too many times as those plastic "hooks" for fastening it together have a tendency to break off.
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rubber_jonnie
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Re: Fixing keyboard mylar sheet/keys

Post by rubber_jonnie »

Yeah, the clips are a bit worrying. The keyboard on the Amstrad NC100 I just bought is really similar with clips everywhere, but uses 2 layer Mylar with contacts both sides rather than carbon pads, so the dome just pushes the 2 sheets together and you don't have the bother of the carbon pads.

I know what you mean about disassembling too often, once I had mine apart I used my multimeter to verify continuity, but you have to be super careful because the meter probes can damage the tracks they are so thin and fragile.

I've found the carbon pad types respond quite well to cleaning with IPA, and that a tiny amount of Electrolube can revive the contacts.

I'd have thought that some sort of conductive resurfacing would work as long as the resistance was not too high.

As for magnification, I found it essential because some of the tracks had damage that was invisible to my eyes. I bought a cheap digital microscope from eBay for £30 with 1000x magnification, built in screen and record to SD card. It has been fantastic.
Collector of many retro things!
800XL and 65XE both with Ultimate1MB,VBXL/XE & PokeyMax, SIDE3, SDrive Max, 2x 1010 cassette, 2x 1050 one with Happy mod, 3x 2600 Jr, 7800 and Lynx II
Approx 20 STs, including a 520 STM, 520 STFMs, 3x Mega ST, MSTE & 2x 32 Mhz boosted STEs
Plus the rest, totalling around 50 machines including a QL, 3x BBC Model B, Electron, Spectrums, ZX81 etc...
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Re: Fixing keyboard mylar sheet/keys

Post by Pacman »

rubber_jonnie wrote: Thu Apr 15, 2021 1:14 pm I know what you mean about disassembling too often, once I had mine apart I used my multimeter to verify continuity, but you have to be super careful because the meter probes can damage the tracks they are so thin and fragile.

I've found the carbon pad types respond quite well to cleaning with IPA, and that a tiny amount of Electrolube can revive the contacts.
Good tip about the multimeter probes. I didn't think about cleaning the pads with IPA (using Q-tips or similar) but well worth doing when I open it again once I've received my "Keypad Fix".
Which Electrolube are you referring to? The liquid conductive silver (I barely have any left of and mostly dried up)?

I find these things hard to get hold of here. I'm about to make a new order of electronic components and am trying to find dealers who have these things but for some reason they're well hidden (or not very common/popular).
I contacted MG Chemicals about the availability of the conductive carbon pen you have and was directed to Circuit Specialists in the UK where it costs UKP 11.98 which is fine. However, they're asking UKP 49.99! :shock: :o
I see it's classified as "UK hazardous goods" when sent locally in the UK (UKP 7.79), so I guess that's the reason.
Strange that I can't get it locally. I would think this sort of thing would be commonly used for repairs, but then again I keep forgetting electronics don't get repaired any longer but discarded :(

As for magnification, I found it essential because some of the tracks had damage that was invisible to my eyes. I bought a cheap digital microscope from eBay for £30 with 1000x magnification, built in screen and record to SD card. It has been fantastic.
That sounds like a useful piece of gear.
I have a digital camera with a microscope function which has helped me a lot with all this.
STe | MonSTer with dual IDE-CF memory card adapter | NEC Multisync 1990SXi | ST_ESSC | RSVE | Link '97 | Sony HD floppy drive/AJAX controller | Exxos HD floppy module | Battery-backed Ricoh realtime clock module | Discovery cartridge | C-Lab Unitor-2 | C-Lab Export | C-Lab Combiner | C-Lab Steady Eye | C-Lab Human Touch | Unicorn USB

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rubber_jonnie
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Re: Fixing keyboard mylar sheet/keys

Post by rubber_jonnie »

@Pacman

No, I'm talking about is this: https://uk.farnell.com/electrolube/eml2 ... ce623f598c

I use it on sockets a lot, but a small amount on a cotton bud (Q-Tip) works really well. Don't use WD40, it's entirely the wrong thing. Another option is DeOxit,but it's twice theprice of

As for the carbon pen, those prices are truly ludicrous. I'd have thought they sell it elsewhere in the world from local stocks at less stupid prices. I'd also expect local alternatives.

Have you tried Amazon? It's where I got mine from.

As for old stuff getting chucked, yes, it really is unnecessary, partially driven by the desire to make things smaller and harder to work on.
Collector of many retro things!
800XL and 65XE both with Ultimate1MB,VBXL/XE & PokeyMax, SIDE3, SDrive Max, 2x 1010 cassette, 2x 1050 one with Happy mod, 3x 2600 Jr, 7800 and Lynx II
Approx 20 STs, including a 520 STM, 520 STFMs, 3x Mega ST, MSTE & 2x 32 Mhz boosted STEs
Plus the rest, totalling around 50 machines including a QL, 3x BBC Model B, Electron, Spectrums, ZX81 etc...
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Re: Fixing keyboard mylar sheet/keys

Post by Pacman »

Unfortunately Amazon tells me it can't send the item to my area. I assume it's because of restrictions because of its contents.
Oh well, I don't need it right now anyway, but would be nice to have for later.

As for "Keypad-fix": great stuff indeed!
I dipped a Q-tip into the jar (looks like dark gray paint) and applied a thin layer to the rubber like keyboard contact (see photo below). Unfortunately it didn't work the first time, but that was entirely my own fault -I didn't thoroughly mix the contents of the jar. After doing that it worked great!
MSTE_keys_contact_fix.jpg
MSTE_keys_contact_fix.jpg (268.56 KiB) Viewed 2299 times
The conductive rubber parts attached to the MSTE keys. One thing worth noting is that there were no visible differences between the malfunctioning key and the rest which were working. I was expecting to see the rubber having worn off, but not so. So the multimeter is your friend here. Also I (carefully) re-attached the mylar sheet to the PCB contacts for testing without putting the big metal part back on (to avoid snapping off the brittle plastic "hooks"). Cumbersome, but doable so I can use the keyboard test from the diagnostic cartridge. If it still doesn't work you can just do it again before you finally reassemble the keyboard.
STe | MonSTer with dual IDE-CF memory card adapter | NEC Multisync 1990SXi | ST_ESSC | RSVE | Link '97 | Sony HD floppy drive/AJAX controller | Exxos HD floppy module | Battery-backed Ricoh realtime clock module | Discovery cartridge | C-Lab Unitor-2 | C-Lab Export | C-Lab Combiner | C-Lab Steady Eye | C-Lab Human Touch | Unicorn USB

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