Membrane keypads again.

[bitrex]

On 05/01/2016 02:37 PM, pfjw@aol.com wrote:

On Sunday, May 1, 2016 at 12:49:54 PM UTC-4, bitrex wrote:
On 05/01/2016 12:26 PM, pfjw@aol.com wrote:
From your description, it is mechanical. Is there a way, using a dental tool or similar that you might test each wire in the loom as it goes into the connector? I expect you will find the problem there.

Peter Wieck
Melrose Park, PA

?

Press down on each separate wire as it goes into the MPC. A spade-type dental tool is excellent for this purpose. The point being that if the connector holds when under stress, but fails when there is no stress, it is very most likely mechanical.

And, of course, it could be two-or-more things if you, in fact, bridged something replacing a resistor.

Peter Wieck
Melrose Park, PA

Question is now that I've located the problem, what's the most effective
way to make an expedient repair? I can't seem to get the wire to make
firm contact no matter how I poke at it, and it seems impossible to pull
out of the header.

I'm thinking about just clipping it off, heat shrinking a longer section
to it and then soldering it directly to the underside of the board, but
that seems a bit barbaric.

 

[bitrex]

On 05/02/2016 07:01 AM, pfjw@aol.com wrote:

On Monday, May 2, 2016 at 6:49:30 AM UTC-4, bitrex wrote:


Question is now that I've located the problem, what's the most effective
way to make an expedient repair? I can't seem to get the wire to make
firm contact no matter how I poke at it, and it seems impossible to pull
out of the header.

I'm thinking about just clipping it off, heat shrinking a longer section
to it and then soldering it directly to the underside of the board, but
that seems a bit barbaric.

The solution that I use for this issue, typically, is to strip a small piece of fine gauge (appropriate to the MPC) copper wire -leave it on the spool for leverage - preferably hardened, and I keep a couple of small spools _only_ for this purpose, and push it down the connector beside the broken wire. Touch this wire with a hot iron and a bit of solder to bridge the break, and then cut it off with fine nippers. If the MPC is very fine, I will pre-tin the wire as it may not flow down the hole. If and then, a bit of hot-melt or similar to insulate any exposed wire. Done.

I have been known to use a silver-plated sewing needle, broken off to the proper length if copper would be too soft. They solder very nicely.

Peter Wieck
Melrose Park, PA

Excellent, will try. Thanks!

 

[bitrex]

On 05/02/2016 07:01 AM, pfjw@aol.com wrote:

On Monday, May 2, 2016 at 6:49:30 AM UTC-4, bitrex wrote:


Question is now that I've located the problem, what's the most effective
way to make an expedient repair? I can't seem to get the wire to make
firm contact no matter how I poke at it, and it seems impossible to pull
out of the header.

I'm thinking about just clipping it off, heat shrinking a longer section
to it and then soldering it directly to the underside of the board, but
that seems a bit barbaric.

The solution that I use for this issue, typically, is to strip a small piece of fine gauge (appropriate to the MPC) copper wire -leave it on the spool for leverage - preferably hardened, and I keep a couple of small spools _only_ for this purpose, and push it down the connector beside the broken wire. Touch this wire with a hot iron and a bit of solder to bridge the break, and then cut it off with fine nippers. If the MPC is very fine, I will pre-tin the wire as it may not flow down the hole. If and then, a bit of hot-melt or similar to insulate any exposed wire. Done.

I have been known to use a silver-plated sewing needle, broken off to the proper length if copper would be too soft. They solder very nicely.

Peter Wieck
Melrose Park, PA

OK, so the mystery deepens a little bit. I was having trouble getting
the shimming to work consistently, so I tried jumpering directly from
the control wire to the underside of the PCB.

Turns out that there's still a problem, even with the wire jumpered
directly to the board. But when I pinch the wire junction in my
fingertips, everything works normally.

Pull-up resistor gone open on that line, maybe?

 

[bitrex]

On 05/02/2016 02:21 PM, bitrex wrote:

On 05/02/2016 07:01 AM, pfjw@aol.com wrote:
On Monday, May 2, 2016 at 6:49:30 AM UTC-4, bitrex wrote:


Question is now that I've located the problem, what's the most effective
way to make an expedient repair? I can't seem to get the wire to make
firm contact no matter how I poke at it, and it seems impossible to pull
out of the header.

I'm thinking about just clipping it off, heat shrinking a longer section
to it and then soldering it directly to the underside of the board, but
that seems a bit barbaric.

The solution that I use for this issue, typically, is to strip a small
piece of fine gauge (appropriate to the MPC) copper wire -leave it on
the spool for leverage - preferably hardened, and I keep a couple of
small spools _only_ for this purpose, and push it down the connector
beside the broken wire. Touch this wire with a hot iron and a bit of
solder to bridge the break, and then cut it off with fine nippers. If
the MPC is very fine, I will pre-tin the wire as it may not flow down
the hole. If and then, a bit of hot-melt or similar to insulate any
exposed wire. Done.

I have been known to use a silver-plated sewing needle, broken off to
the proper length if copper would be too soft. They solder very nicely.

Peter Wieck
Melrose Park, PA


OK, so the mystery deepens a little bit. I was having trouble getting
the shimming to work consistently, so I tried jumpering directly from
the control wire to the underside of the PCB.

Turns out that there's still a problem, even with the wire jumpered
directly to the board. But when I pinch the wire junction in my
fingertips, everything works normally.

Pull-up resistor gone open on that line, maybe?

Yup, that was it. Pullup resistor on that pin has gone bad!

 

[Gareth Magennis]

"bitrex" wrote in message news:b2NVy.66828$Bn7.1297@fx26.iad...

On 05/02/2016 02:21 PM, bitrex wrote:

On 05/02/2016 07:01 AM, pfjw@aol.com wrote:
On Monday, May 2, 2016 at 6:49:30 AM UTC-4, bitrex wrote:


Question is now that I've located the problem, what's the most effective
way to make an expedient repair? I can't seem to get the wire to make
firm contact no matter how I poke at it, and it seems impossible to pull
out of the header.

I'm thinking about just clipping it off, heat shrinking a longer section
to it and then soldering it directly to the underside of the board, but
that seems a bit barbaric.

The solution that I use for this issue, typically, is to strip a small
piece of fine gauge (appropriate to the MPC) copper wire -leave it on
the spool for leverage - preferably hardened, and I keep a couple of
small spools _only_ for this purpose, and push it down the connector
beside the broken wire. Touch this wire with a hot iron and a bit of
solder to bridge the break, and then cut it off with fine nippers. If
the MPC is very fine, I will pre-tin the wire as it may not flow down
the hole. If and then, a bit of hot-melt or similar to insulate any
exposed wire. Done.

I have been known to use a silver-plated sewing needle, broken off to
the proper length if copper would be too soft. They solder very nicely.

Peter Wieck
Melrose Park, PA


OK, so the mystery deepens a little bit. I was having trouble getting
the shimming to work consistently, so I tried jumpering directly from
the control wire to the underside of the PCB.

Turns out that there's still a problem, even with the wire jumpered
directly to the board. But when I pinch the wire junction in my
fingertips, everything works normally.

Pull-up resistor gone open on that line, maybe?

Yup, that was it. Pullup resistor on that pin has gone bad!





I said that quite some time ago.


R66 is most likely contrast or viewing angle adjustment.
It might be a good idea to check all the pullup resistors (RA3) are all
present and correct.



Gareth.