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| Author |
Message |
scg
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Broken comma key
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Aug 8 05:56 UTC 1994 |
The comma key on my portable computer has stopped working, and I'm
wondering if there's likely to be an easy way to fix it. The computer is
a Toshiba T3100. It's a rather heavy and bulky 286-8 portable with an
internal power supply and no battery from about seven years ago. I don't
know whether the key is fixable, or whether the keyboard is still made. Is
this likely to be fixable? I don't want to put much money into a computer
of that age, but I would like to get it working again.
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| 22 responses total. |
kentn
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response 1 of 22:
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Aug 8 07:02 UTC 1994 |
Depending on how difficult it is to get the keyboard out of the case,
and how strange the keyswitches are, there's a chance you can buy
a keyswitch or three (nice to have a couple spares) and replace the
faulty one. I have a feeling, though, that the need to make a portable
as small as possible means the keyboard may be difficult to repair
at the switch level. In that case, you'd have to replace the whole
keyboard (probably not worth it unless you can find another Toshiba
with a working keyboard but dead everything else for cheap).
The easy keyboards to fix are the ones with keyswitch assemblies
attached to a printed circuit board. Just desolder the switch
contacts, replace with a new switch, and solder. Even if you can't
find a keyswitch to work, you can sometimes swap another less-used
keyswitch out of the board (something like your second control key
or some character you never use).
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n8nxf
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response 2 of 22:
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Aug 8 12:07 UTC 1994 |
Keyboard switches usually fail because dirt has gotten between the
contacts inside them. Sometimes all you have to do is pry the key-
cap off the switch to expose the contacts. Other times it may require
removing the switch from the PC board and then taking it apart (Or
replace as noted above.)
Use tweezers to remove any dirt/hair/etc. from inside the coatact
area. Then put a drop of color TV tuner cleaner (Radio Shack) on
the contacts themselves to clean off any ozide. Try that key,
if possible, before reassembly. I've done this several times with
good success.
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scg
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response 3 of 22:
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Aug 8 16:17 UTC 1994 |
I know the keyboard's easy to get out of the case, because I had to take
it out afew months ago to replace the clock battery, which is under it. I
thought of cleaning the key, but I wonder if it's the problem given how
differently it failed from the return key on my desktop computer, which
was fixed by cleaning the contacts. On the desktop computer, the key
stopped working gradually (it worked sometimes and not others, or took a
few hits to get it to register), but this one just stopped working very
suddenly. Are both of those typical reactions for a dirty contact?
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rcurl
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response 4 of 22:
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Aug 8 17:12 UTC 1994 |
There may be a bug in the switch.
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kentn
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response 5 of 22:
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Aug 8 18:00 UTC 1994 |
I've seen keyswitches fail both ways (intermittently and suddenly).
Sometimes cleaning helps, sometimes not. Try it, but personally, I'd
try to find a couple replacement keyswitches just in case...
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scg
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response 6 of 22:
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Aug 9 03:59 UTC 1994 |
I pulled the cap off the key and found that the switch is pretty fully
enclosed and there didn't seem to be an obvious way to get it open. I
tried dripping in a little bit of rubbing alcohol, since that's what
switched the return key on my desktop computer, but it didn't help. I'm
not sure exactly what to unsolder to get the keyswitch off, and for
obvious reasons do not want to screw up and unsolder the wrong thing.
Maybe, before I go further, now would be the time to ask if anybody out
there has an otherwise dead Toshiba T3100 (or something else using the
same keyboard) with a working keyboard.
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n8nxf
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response 7 of 22:
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Aug 9 12:06 UTC 1994 |
I'd say take it all apart and see what there is to see! Just be sure you
can get it all back together again ;-) (I just happened to have taken my
mom's XT keyboard apart last night because some of the keys were flakey.
It turned out to be a capacitive keyboard! A 3/8" dia. aluminum foil
disk is brought in contact with a couple of PC foil pads ecthed into the
board and covered with green paint (solder mask). No electric contacts!
I've also run across inductive keyboards where a ferrite bead is lowered
into a single turn coil, etched into the PC board, when a key is pressed.
It is also not uncommon to see silicone membrane keyboards where carbon
pads, on the bottom side of the membrane, make contact with gold plated
contacts on the PC board when a key is pressed. There are also many types
of contacts used. All look more or less the same until you take them
apart.)
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rcurl
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response 8 of 22:
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Aug 10 05:23 UTC 1994 |
Are all of those repairable? I haven't taken a keyboard apart, but
many components are heat-welded together, or otherwise assembled so
disassembly is destructive. (I tried to repair a steam iron, but it
was difficult to separate the upper body from the heat plate - eventually
enough force discovered that they were *glued* together with silicone to
form the water chamber. Live and learn.....)
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scg
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response 9 of 22:
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Aug 10 05:57 UTC 1994 |
I couldn't figure out how to get the key apart without risking breaking
anything, so I'm very hesitant to try it. I also don't have a clue what
to unsolder to get the key off the circuit board, nor do I particularly
like the idea of doing that myself.
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kentn
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response 10 of 22:
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Aug 10 06:40 UTC 1994 |
The keyswitches I'm familiar with repairing (replacing) are those
similar to the ones made by Microswitch (small plastic sealed cube with
two or four pins on the bottom and a spring-loaded plunger for the
keycap to connect to on the top). You need access to the bottom of the
circuit board, and finding which contacts to unsolder can be a bit
frustrating since they are often on one edge of the cube--so it's not
always easy to see if you are unsoldering the key you want or the one
next to it. A de-soldering tool is almost mandatory. Low wattage iron
is needed, too. It is helpful to remove the keycaps from the bad key
as well as from surrounding keys. A small prying tool (I like to use a
small x-acto knife) can be helpful for prying and probing (though you
wouldn't want to cut anything).
I've seen some keyboard circuit boards that have a piggyback circuit
board on their bottom side. That would normally need to be removed
if it blocks access to the contacts you are looking for. I doubt,
though, that you'll see that on a laptop.
Those membrane type switches sound like a pain. As Rane asks, are
they repairable? I don't know; I doubt it would be easy, though.
Do you know what type of keyswitch you are dealing with, scg?
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scg
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response 11 of 22:
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Aug 10 06:55 UTC 1994 |
The keyswitch is a box with black plastic sides and a metal top. The
metal on the top also goes down the sides to hold it on, but there doesn't
seem to be an easy way to take it off. The thing that the key cap hooks
onto is a plastic stick that is oval shape. As for what kind of
connection it makes inside, I don't know as I haven't been able to open
it. There is no problem getting access to the bottom of the circuit
board, but I'm not sure what there to unsolder or how to do the
unsoldering safely.
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n8nxf
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response 12 of 22:
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Aug 10 12:21 UTC 1994 |
Perhaps it's time to have a computer fix-it shop take a look at it?
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kentn
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response 13 of 22:
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Aug 10 19:56 UTC 1994 |
That would seem to be the best bet
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curby
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response 14 of 22:
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Aug 11 05:45 UTC 1994 |
Or, if you slip me $20, I will get you a new 101 key keyboard! 8^)
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scg
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response 15 of 22:
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Aug 11 05:47 UTC 1994 |
I've got a 101 key keyboard, and it works just fine. It just won't fit in
the portable.
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matts
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response 16 of 22:
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Aug 17 19:53 UTC 1994 |
you could always buy a tiny spst push-button switch (momentary)
at radio shit...
jsut drill through the old key, and thread the switch through..
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scg
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response 17 of 22:
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Sep 4 06:15 UTC 1994 |
It's fixed! TS came over this evening and spent two hours working on it,
finally ending up unsoldering the key and replacing it with another key
that I never use. It's great to be able to use a computer at home again
(the monitor on my desktop computer is also broken now).
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tsty
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response 18 of 22:
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Sep 5 08:40 UTC 1994 |
Hey, it was a fun 2 hours. But it did tax my soldering/desoldering
techniques a bit. Even though those things are permanently etched, they
are physical/visual adn mental skills that (I found out) +can+ get
a bit rusty without use every now and then (phew!).
And we weren't on a bench ... with a magnifying lamp ... nor did we
have either of the usual sets of "third hands" ... my soldering iron
was overheating (no temp controls on that one) ... gravity was no
assistant but rather a detriment ..... I guess we got a little bit
lucky with this one.
I had to holda NASA hand-soldering cert to do my work in the military.
All sorts of things were flashing back as we did the switch swap, well,
half a swap anyway - no use putting the bad switch back in anywhere.
BTW - does anyone know what the use is for the Sys Req key on a
keyboad for ms-dos machines? That's the switch we used for a sub and
left Sys Req empty.
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rcurl
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response 19 of 22:
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Sep 5 19:11 UTC 1994 |
Omigod, you didn't take that key, did you? That's the key that inter-
digitates the flammogler array, when the system hyperventilates!
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kentn
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response 20 of 22:
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Sep 6 00:26 UTC 1994 |
I think you picked a good key to swap, TS. To my knowledge the only
time I've ever used the Sys Req key was to punch it once to see what
got trashed/garbled/locked up (nothing as it turned out). The only
gotcha is that on the two keyboards I've got handy with Sys Req keys,
that is also the Print Screen key (which if you use it like I do you
won't miss it much, or can get some keyboard re-mapping utility and
make some other key combination work for that).
I read somewhere what the Sys Req stood/stands for (system request or
something like that). I think it's an IBM mainframe-ism from the dark
ages... I'll let someone with an older memory than mine fill us all
in.
My soldering fun today was soldering a leg back onto the jumper block
of one of my SSC's. Tack, tack, tack, arghhh..., dammit, tack, tack,
Yeah! I'm not messing with that one again if I can help it.
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scg
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response 21 of 22:
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Sep 6 02:01 UTC 1994 |
I would not have wnted to take the sys req key off my other keyboard,
where it is the same as the print screen key, but this computer had a
completely seerate sys req key. We picked it because it was the only key
on the whole keyboard that I had never used.
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tsty
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response 22 of 22:
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Dec 20 17:54 UTC 1994 |
In fact, scg did all the picking - i just took orders ......
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