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TRS-80 Model 4 Keyboard repair

I was wondering if anyone has some suggestions.  I have a TRS-80 model 4 wi=
th a membrane keyboard.  The ribbon cable has two broken traces.  Does anyo=
ne have any suggestion on how repair the ribbon?  FYI, the ribbon cable is =
the same material as the membrane in the keyboard, i.e. one big piece.

Thanks
   David
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David
11/11/2016 10:11:44 PM
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On Friday, November 11, 2016 at 4:11:45 PM UTC-6, David Jones wrote:
> I was wondering if anyone has some suggestions.  I have a TRS-80 model 4 =
with a membrane keyboard.  The ribbon cable has two broken traces.  Does an=
yone have any suggestion on how repair the ribbon?  FYI, the ribbon cable i=
s the same material as the membrane in the keyboard, i.e. one big piece.
>=20
> Thanks
>    David

I haven't done this, but depending on your skill level with soldering irons=
 and such, it may be possible. it also depends where the foil trace is brok=
en. You could take a x-acto  knife to cut the membrane around the open trac=
e and solder strands from a small gauge wire and recover with heavy packing=
 tape. Or you may be able to solder a piece of wire point to point from ckt=
 board to connector. there are more possibles but I am tired of typing with=
 one hand (broken arm). Post a pic and maybe a better suggestion will show =
up.
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bryan
11/12/2016 7:50:06 PM
On Sun, 13 Nov 2016, David Jones wrote:

> Well the plastic isn't Mylar so it melts pretty easily.  But I'm going 
> to try and solder it anyways and see what happens.  At this point, it's 
> ether that or see if I can use a conductive glue and solder a wire down. 
> That is assuming I can expose the conductors and get a good connection. 
> Well my last resort idea is make a PS2 keyboard interface to the 
> existing connector.  I'm going to take it slow so I don't make thing 
> worse.
>
Be careful.  My KIM-1 keyboard needed some work, and I tried to solder 
around the problem, and melted the plastic or whatever it was.  So be 
careful.

   Michael

> A little more of the story.  This was an ebay item that was supposed to 
> be working.  It wasn't completely.  The video was out of adjustment and 
> the power supply had bad solder joints on the connector.  Both easy 
> fixes.  The worst was a mouse had chewed on the lines going to the power 
> switch and keyboard ribbon.  That last item is the only thing that's 
> been hard to fix.
>
> David
>
>
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Michael
11/14/2016 1:01:01 AM
Well the plastic isn't Mylar so it melts pretty easily.  But I'm going to t=
ry and solder it anyways and see what happens.  At this point, it's ether t=
hat or see if I can use a conductive glue and solder a wire down.  That is =
assuming I can expose the conductors and get a good connection.  Well my la=
st resort idea is make a PS2 keyboard interface to the existing connector. =
 I'm going to take it slow so I don't make thing worse.

A little more of the story.  This was an ebay item that was supposed to be =
working.  It wasn't completely.  The video was out of adjustment and the po=
wer supply had bad solder joints on the connector.  Both easy fixes.  The w=
orst was a mouse had chewed on the lines going to the power switch and keyb=
oard ribbon.  That last item is the only thing that's been hard to fix.

David

0
David
11/14/2016 2:04:30 AM
On Monday, November 14, 2016 at 12:43:07 PM UTC-5, Michael Black wrote:
> On Sun, 13 Nov 2016, David Jones wrote:
> 
> > Well the plastic isn't Mylar so it melts pretty easily.  But I'm going 
> > to try and solder it anyways and see what happens.  At this point, it's 
> > ether that or see if I can use a conductive glue and solder a wire down. 
> > That is assuming I can expose the conductors and get a good connection. 
> > Well my last resort idea is make a PS2 keyboard interface to the 
> > existing connector.  I'm going to take it slow so I don't make thing 
> > worse.
> >
> Be careful.  My KIM-1 keyboard needed some work, and I tried to solder 
> around the problem, and melted the plastic or whatever it was.  So be 
> careful.
> 
>    Michael
> 
> > A little more of the story.  This was an ebay item that was supposed to 
> > be working.  It wasn't completely.  The video was out of adjustment and 
> > the power supply had bad solder joints on the connector.  Both easy 
> > fixes.  The worst was a mouse had chewed on the lines going to the power 
> > switch and keyboard ribbon.  That last item is the only thing that's 
> > been hard to fix.
> >
> > David
> >
> >

Yep, been there before too.  

Well I just tried a small test solder and it was a no-go.  The plastic just melted like I was afraid it would do. So back to the drawing board.
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David
11/15/2016 2:57:52 AM
Well I got the keyboard working.  Below is what I did in case someone else =
runs into this problem

Took a X-acto knife and very carefully cut away the plastic over the trace =
that need to be repaired.  I did it as close to the damage as possible and =
it also too some scrapping to expose the traces. It really helps if you hav=
e a hands free magnifying glass.

Then I cut a piece of 30 gauge wire to fit, stripped the ends, then spot gl=
ued it down with super glue just short of the stripped part.

Once things were glued down so it wouldn't move around, I used some "Silver=
 Conductive Paste Glue Wire Adhesive Paint PCB Repair For LCD 0.3ML USA" I =
got from ebay to make the connection from the original trace to the wire.

After this had dried and set, I tested the continuity. If it didn't take, r=
inse and repeat.

With the traces repair and tested, I then covered that section with thin ca=
rdboard pieces taped together.  This was to keep it from flexing and poppin=
g the connections lose.

The only other problem I ran into was some cross talk once I tried it live =
in the computer.  This showed up as if all the buttons on the repaired line=
 were pressed.  Turns out this was caused by the bracket that covers the ca=
ble as it enters the motherboard cage.  To fix that, I put a piece of thin =
cardboard between the cable and the bracket.  Not sure why it only showed u=
p on the repaired line but its all happy now.

Well I discovered two other problems with the computer.  One was the focus =
pot on the video board was arcing.  The other was the original floppy drive=
s.  The head rails need to be cleaned and lubed.

0
David
11/27/2016 8:59:45 PM
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