Model 4 keyboard problem

Model 4 keyboard problem

Post by Jeffrey Shar » Tue, 23 Apr 2002 01:15:41



So I acquire this nice TRS-80 Model 4 with 128K. It works, except for this
annoying keyboard problem. The key action is good for all keys; they go down
with a minimum of pressure and spring back up very quickly. The problem is
that some keys have to be pressed _very_ hard for the computer to sense the
keypress -- so hard that it noticeably bends the keyboard PCB each time.

I'm thinking that there could be a bad solder connection somewhere on the
keyboard PCB, that the connection is made when the bending of the board
causes the correct leads to be brought into contact with each other. How
far-fetched is this?

What else could be causing my problem? Google has not returned anything
useful.

--
Jeffrey Sharp

 
 
 

Model 4 keyboard problem

Post by B » Tue, 23 Apr 2002 02:27:20




Quote:>So I acquire this nice TRS-80 Model 4 with 128K. It works, except for this
>annoying keyboard problem. The key action is good for all keys; they go down
>with a minimum of pressure and spring back up very quickly. The problem is
>that some keys have to be pressed _very_ hard for the computer to sense the
>keypress -- so hard that it noticeably bends the keyboard PCB each time.

>I'm thinking that there could be a bad solder connection somewhere on the
>keyboard PCB, that the connection is made when the bending of the board
>causes the correct leads to be brought into contact with each other. How
>far-fetched is this?

>What else could be causing my problem? Google has not returned anything
>useful.

>--
>Jeffrey Sharp

I've got a Model 4 where every key worked. Didn't use it for two
years, kept it in a spare bedroom... Finally got some tables to setup
my computers for display, and most of the keys didn't work. Found same
issue you did. If I press hard (or tap them hard), they work.
Eventually, many of them kept working. Must be oxidation at work here,
and the repeated use cleared up the trouble with the exception of one
or two keys. I suspect if I used it daily, the trouble would
disappear.
Some of my systems fared better. The Apple IIe for example NEVER
exhibits a problem nor does my old 386, that were both stored in the
same room. Neither did the Commodores or Tandy Cocos, but the Atari
800 has ALWAYS exhibited the problem if I don't use it constantly.
My TIs generally exhibit the problem  for a few minutes, but then are
ok.
The 4p on the other hand has never had a problem...

 
 
 

Model 4 keyboard problem

Post by Mo » Tue, 23 Apr 2002 10:27:32


You sound quite a bit like me- a real multi-platformer! I too have an Atari
800, Atari 800XL, TRS-80 model 3, model 4, model 1, Coco2, Coco 1, Commodore
64. Plus numerous disk drives, tape drives, printers, plotters, and modems.
I've had the same experience with keyboards, the only problems I've had have
been with the Model 4 and the Atari 800. The Atari clears up very quickly if
I give it a good workout like typing in a program from a magazine. The model
4's got so bad I pulled a keyboard from an extra model 3 and have been
getting by with it (no control key, no function keys 8-).
I've been meaning to snatch one of those from Computer news80, they have new
ones for $15.00 but I'm very cheap and very lazy when it comes to mail
order.

Mo




>>So I acquire this nice TRS-80 Model 4 with 128K. It works, except for this
>>annoying keyboard problem. The key action is good for all keys; they go
down
>>with a minimum of pressure and spring back up very quickly. The problem is
>>that some keys have to be pressed _very_ hard for the computer to sense
the
>>keypress -- so hard that it noticeably bends the keyboard PCB each time.

>>I'm thinking that there could be a bad solder connection somewhere on the
>>keyboard PCB, that the connection is made when the bending of the board
>>causes the correct leads to be brought into contact with each other. How
>>far-fetched is this?

>>What else could be causing my problem? Google has not returned anything
>>useful.

>>--
>>Jeffrey Sharp

>I've got a Model 4 where every key worked. Didn't use it for two
>years, kept it in a spare bedroom... Finally got some tables to setup
>my computers for display, and most of the keys didn't work. Found same
>issue you did. If I press hard (or tap them hard), they work.
>Eventually, many of them kept working. Must be oxidation at work here,
>and the repeated use cleared up the trouble with the exception of one
>or two keys. I suspect if I used it daily, the trouble would
>disappear.
>Some of my systems fared better. The Apple IIe for example NEVER
>exhibits a problem nor does my old 386, that were both stored in the
>same room. Neither did the Commodores or Tandy Cocos, but the Atari
>800 has ALWAYS exhibited the problem if I don't use it constantly.
>My TIs generally exhibit the problem  for a few minutes, but then are
>ok.
>The 4p on the other hand has never had a problem...

 
 
 

Model 4 keyboard problem

Post by Amardeep S Chan » Tue, 23 Apr 2002 12:21:05



Quote:> So I acquire this nice TRS-80 Model 4 with 128K. It works, except for this
> annoying keyboard problem. The key action is good for all keys; they go
down
> with a minimum of pressure and spring back up very quickly. The problem is
> that some keys have to be pressed _very_ hard for the computer to sense
the
> keypress -- so hard that it noticeably bends the keyboard PCB each time.

> I'm thinking that there could be a bad solder connection somewhere on the
> keyboard PCB, that the connection is made when the bending of the board
> causes the correct leads to be brought into contact with each other. How
> far-fetched is this?

> What else could be causing my problem? Google has not returned anything
> useful.

Keyboard failure is probably the number one reliability problem with the
Models I, III, and 4.  Usually it is the contacts themselves that develop a
problem.  I've repaired quite a few in the last few years, both membrane and
mechanical.  I'm presently queued up to repair 3 keys on my primary Model I.
Six months of disuse and kaput.  Ah well.

Let us know which type of keyboard it is and I'm sure detailed instructions
for repair can be provided.

 
 
 

Model 4 keyboard problem

Post by Mo » Tue, 23 Apr 2002 13:30:02


My model 4 has the type of keyboard in which every switch is soldered to the
board on one side and on the other are clips on every switch keeping it in a
sandwich. I cannot figure out how to open this sandwich up without
desoldering every switch or putting it in some type of jig that would open
all of the clips simultaneously. Sorry I don't have it in front of me for a
board number, but it came out of an early model 4 (black and white) I guess
non-gate array.
Mo

>Let us know which type of keyboard it is and I'm sure detailed instructions
>for repair can be provided.

 
 
 

Model 4 keyboard problem

Post by Jeffrey Shar » Tue, 23 Apr 2002 15:26:43


Quote:> Keyboard failure is probably the number one reliability problem with
> the Models I, III, and 4. Let us know which type of keyboard it is
> and I'm sure detailed instructions for repair can be provided.

Sure! It is the non-gate-array version, catalog number 26-1069.

--
Jeffrey Sharp

 
 
 

Model 4 keyboard problem

Post by John Moska » Wed, 24 Apr 2002 00:22:14


I would suggest pulling the keyboard and examining it for a cracked board. If
you press to * those keys, you will break it. I have not opened a model 4
in years, but I do remember that problem well.

> So I acquire this nice TRS-80 Model 4 with 128K. It works, except for this
> annoying keyboard problem. The key action is good for all keys; they go down
> with a minimum of pressure and spring back up very quickly. The problem is
> that some keys have to be pressed _very_ hard for the computer to sense the
> keypress -- so hard that it noticeably bends the keyboard PCB each time.

> I'm thinking that there could be a bad solder connection somewhere on the
> keyboard PCB, that the connection is made when the bending of the board
> causes the correct leads to be brought into contact with each other. How
> far-fetched is this?

> What else could be causing my problem? Google has not returned anything
> useful.

> --
> Jeffrey Sharp

 
 
 

Model 4 keyboard problem

Post by Amardeep S Chan » Wed, 24 Apr 2002 12:55:29



Quote:> > Keyboard failure is probably the number one reliability problem with
> > the Models I, III, and 4. Let us know which type of keyboard it is
> > and I'm sure detailed instructions for repair can be provided.

> Sure! It is the non-gate-array version, catalog number 26-1069.

No, that's the computer type.  The keyboard type can only be determined by
removing and examining it.  Does it have individually soldered keyswitches,
or is it a monolithic membrane type?
 
 
 

1. Model 4 keyboard problems

Hello

I have a model 4 and some of the keys on the keyboard are dead. I used
to be an electronics tech so I disassembled the Model 4 and examined the
dead key mechanisms. They are relatively easy to get apart. Inside was a
shaft with a spring on it attached to a rubber cup. Inside the rubber
cup was a rubber button similar to what used to be in the old calculator
keypads. I tried cleaning the button and contacts as I used to do on the
calculators years ago but without any luck. I had ten dead or poor
working keys so I robbed the keys from the numeric keypad to replace
them. This restores the use of the main keyboard but I miss the numeric
keypad. Also I have several more keys that work poorly after you leave
them for a while.

Does anyone know if there is a special way to clean the key mechanisms?
I suspect that the conductive coating on the buttons is relatively thin
and may have worn off leaving only the rubber button. All key locations
work fine when tested with a known good key mechanism so I know the
keyboard itself is working. Is there a better quality keyboard that was
used on the some of the model 4s? I remember there being a couple of
different ones on the model 1.

Any help would be appreciated.

Thanks

Andy :)

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