Fixing keyboard mylar sheet/keys

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Pacman
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Fixing keyboard mylar sheet/keys

Post by Pacman »

I've located a broken trace to my Mega STe keyboard causing the spacebar not to work. And the "help" key isn't working all the time. I used the keyboard test from the diagnostic cartridge to check all keys (it even checks the mouse!).

Closer inspection reveals that the keys have a black rubbery sort of coating which in turn comes in contact with the mylar sheet when you press them, and for the "help" key the contact ends are silvery (I assume the rubber has worn off). I noticed the "Undo" key looked the same, but with that one both ends of the rubbery contact were equally silvery (unlike the "Undo" key which was partly black on one side). I read in a similar thread about the importance of even heights on each side of the contacts which of course makes perfect sense.

My question is: what should I use to fix this? There's conductive paint, conductive glue, some sort of liquid silvery stuff for fixing PCBs, some sort of specialized keypad fixer solution etc. I believe I bought some conductive pant/glue a while back and will see what I can find in my toolbox, but does it matter what I use as long as it's conductive and you can "paint" it on, and should I use different things for the broken circuit trace on the mylar sheet, the keyboard contacts (where the back rubbery material is) and on the mylar sheet's contact pads (also black)?
Does Exxos sell anything suitable for this in case I don't find anything suitable I already have?
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Re: Fixing keyboard mylar sheet/keys

Post by exxos »

I used to sell the stuff but it got too expensive to buy in bulk..

You need keypad fix glue for the keys...http://keypadfix.com/
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viewtopic.php?f=17&t=1585 Have you done the Mandatory Fixes ?
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Re: Fixing keyboard mylar sheet/keys

Post by rubber_jonnie »

This is what I used to fix my MSTE ctrl key: https://www.amazon.co.uk/MG-Chemicals-8 ... _d_rp_24_t
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 »

I just found a few things which might be suitable for fixing it. Please feel free to comment so I don't end up using the wrong products.
  1. Anders products Wire Glue (and a projects page)
    It says "Micro-carbon based" on the jar and apparently suitable for electronic repairs.

    Wire Glue Pack.gif
    Wire Glue Pack.gif (31.07 KiB) Viewed 3411 times
  2. Similar to the above, but in a thin syringe.
    No brand name, and came only in a small red plastic zip bag along with a couple of wooden application sticks, wooden coctail stick and a small piece of paper explaining how to use it. It refers to it as "wire glue" but I have no idea where I got it from, what it contains or who manufactured it. Maybe someone reading can recognize it?

    wireglue_syringe.jpg
    wireglue_syringe.jpg (237.69 KiB) Viewed 3411 times
  3. Loctite 3863 Circuit+ car rear windscreen defogger repair kit.
    Contains silver according to the datasheet.

    Loctite_3863.png
    Loctite_3863.png (336.87 KiB) Viewed 3411 times
  4. Electrolube silver conductive paint
    I've had this little bottle probably close to 35 years! Not sure about the shelf life, but it might still be OK. I think I've used it for PCB repairs in the past. I suppose it's similar to the Loctite above.

    electrolube_silver_paint.jpg
    electrolube_silver_paint.jpg (190.67 KiB) Viewed 3411 times
Is any of this suitable for repairing the keyboard?
Perhaps the carbon based "wire glue" is best for the keyboard contacts (and black contact pads on the mylar sheet if I find any of them worn out), and the silver conductive paint (Loctite or Electrolube)?

rubber_jonnie wrote: Tue Apr 13, 2021 10:57 am This is what I used to fix my MSTE ctrl key: https://www.amazon.co.uk/MG-Chemicals-8 ... _d_rp_24_t
It looks easy to fix PCB traces neatly with that pen type applicator! Was it used to fix the black rubbery parts in the key itself or the circuit trace on the mylar sheet?

exxos wrote: Tue Apr 13, 2021 10:41 am I used to sell the stuff but it got too expensive to buy in bulk..

You need keypad fix glue for the keys...http://keypadfix.com/
So this is only for the black rubbery parts on the keys and the black pads on the mylar sheet? Or can it be used to repair a broken PCB trace on the mylar sheet as well?
From what I read about it, it's carbon based, so maybe that "wire glue" I already have might be similar?
I tried to find a solution on Youtube and someone had used "Remote restore" for this. My guess is they're all quite similar, but don't want to make too many guesses with all this. Apparently Best electronics had mylar sheet replacements but they're now sold out according to their website, so repairing is the way to go.

EDIT: looking closer it occured to me that the silvery surface of the "Undo" and "Help" keys isn't something that has been worn away, exposing its surface but rather my attempt of fixing them years ago with that silver conductive Electrolube paint. It appears to have fallen off in flakes, so apparently it doesn't stick very well to what looks like rubber....
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Re: Fixing keyboard mylar sheet/keys

Post by exxos »

pink bag looks like one of the kits I used to sell a long time ago, I don't ever remember selling it in a syringe. as it says "wire glue" it is for repairing carbon tracks on keyboards.

Keypad fix is for fixing the carbon conductive part of the rubber keys..
https://www.exxosforum.co.uk/atari/ All my hardware guides - mods - games - STOS
https://www.exxosforum.co.uk/atari/store2/ - All my hardware mods for sale - Please help support by making a purchase.
viewtopic.php?f=17&t=1585 Have you done the Mandatory Fixes ?
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Re: Fixing keyboard mylar sheet/keys

Post by Pacman »

exxos wrote: Tue Apr 13, 2021 12:40 pm pink bag looks like one of the kits I used to sell a long time ago, I don't ever remember selling it in a syringe. as it says "wire glue" it is for repairing carbon tracks on keyboards.

Keypad fix is for fixing the carbon conductive part of the rubber keys..
You're right!
I had ordered something entitled "CONDUCTIVE WIRE GLUE / PAINT" for UKP 5 back in 2017 with the bag marked as item# 75, so this must have been it.

By "carbon tracks" you're referring to the black pads on the mylar sheet?
But the carbon conductive rubbery parts of the keys can't be fixed with the same thing?
And for a broken PCB track on the mylar sheet, would any of these be suitable?

Where did you order keypad fix from back when you sold it?
Shipping costs from the U.S. are outrageous, so I hope there are European distributors for this. Unfortunately I haven't been able to find it (nor the pen rubber_jonnie mentioned locally. At least not something for the general public although it might be available for the electronics industry.
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Re: Fixing keyboard mylar sheet/keys

Post by rubber_jonnie »

@Pacman I used the pen to fix the tracks.

When my mylar sheet/keyboard was made a crease was added in that caused a resistive effect in the metal trace, which heated up and failed. I also found a 2nd problem that looked the same further down the same trace.

I used a fibreglass pen to clean the track either side of the damage then used the pen to draw a new trace.

I expect it might work on the mylar carbon pads, though not so sure about the rubber pads for the keys as it does dry quite hard and inflexibly.

I wouldn't bother with the stuff in the pink bag/syringe, I had some and it was crap!!!
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: Tue Apr 13, 2021 1:05 pm @Pacman I used the pen to fix the tracks.

When my mylar sheet/keyboard was made a crease was added in that caused a resistive effect in the metal trace, which heated up and failed. I also found a 2nd problem that looked the same further down the same trace.
Not the best quality control back in those days... "Power without the qual.." ahem... "price" I mean :lol:
Glad you got it working though.
I used a fibreglass pen to clean the track either side of the damage then used the pen to draw a new trace.
Yeah, those are nice! I've used them a lot for PCB repairs.

I expect it might work on the mylar carbon pads, though not so sure about the rubber pads for the keys as it does dry quite hard and inflexibly.

I wouldn't bother with the stuff in the pink bag/syringe, I had some and it was crap!!!
I got the non-working spacebar to work again!
The Loctite conductive silver had dried up, so that was of no use, but the old bottle of Electrolube silver conductive paint still had some in it (half dried up though), so I used some masking tape and made a nice new track on top of the broken part. Resistance got lower as it dried, but fearing it might all crack up I put some new masking tape around the trace (a little further out this time, allowing for a wider track) and used the small "Wire glue" can (not the syringe) to cover it, hoping this would somehow encapsulate the silver paint underneath.

It all works fine now except for the "Undo" key, but I'm sure that can be fixed with "Keypad fix". I suppose the "Wire Glue" in the pink bag/syringe is the same thing as in the white can of Wire Glue. How did you find it to be crap? Did it dry up/fall off or not work at all?
I'm guessing that the special thing about "Keypad fix" is that it sticks to rubber and is flexible unlike the other types of conductive material.
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Re: Fixing keyboard mylar sheet/keys

Post by rubber_jonnie »

Pacman wrote: Tue Apr 13, 2021 8:45 pm
How did you find it to be crap? Did it dry up/fall off or not work at all?
I'm guessing that the special thing about "Keypad fix" is that it sticks to rubber and is flexible unlike the other types of conductive material.
Good stuff.

The stuff in the pink bag was near impossible to apply as it was too thick and the needle too narrow, plus the stuff I had never dried.

The carbon pen was way better as it was as simple as drawing your own circuit. I did leave it 24hrs and covered it in in kapton tape before reassembly, and no problem since.
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: Tue Apr 13, 2021 11:42 pm
Pacman wrote: Tue Apr 13, 2021 8:45 pm
How did you find it to be crap? Did it dry up/fall off or not work at all?
I'm guessing that the special thing about "Keypad fix" is that it sticks to rubber and is flexible unlike the other types of conductive material.
Good stuff.
I just ordered a "Keypad fix" after finally finding a UK eBay dealer who had it and could send overseas.
That should take care of the worn rubber contact inside the "Help" key.

The stuff in the pink bag was near impossible to apply as it was too thick and the needle too narrow, plus the stuff I had never dried.

The carbon pen was way better as it was as simple as drawing your own circuit. I did leave it 24hrs and covered it in in kapton tape before reassembly, and no problem since.
I just noticed that my syringe was empty! I must have used it for something years ago, but can't remember the result.
I've just tried applying a little of that "Wire Glue" plastic can though, to a piece of plastic for testing. I applied a thin layer and let it try (looks very matte) and it did give continuity, so maybe this is something else than the stuff inside the syringe, even though they shared the same name.
It might be suitable for the black (carbon?) contacts on the mylar sheet in case any of those are found to be worn.

I looked up the MG chemicals website for the carbon pen you have and see that they have 3 types: carbon, nickel and silver. Silver apparently has the lowest resistance (but I assume it's also the most expensive) while nickel is OK for fixing short PCB traces. The one you have is more resistive but also appears to be OK for short distances.
Kapton tape is a great idea -I've never used it myself, but have heard much good about it and is probably worth adding to my next electronic component order.
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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