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Touch pad not behaving!!

noquacks

Jun 26, 2013
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People,

I have a pH meter at work, from 2017. The touch pad that scrolls up/down values is so wacky it has become unbearable. The meter itself is still good, it's just that entering values via the touch pad that frustrates me. When you press the UP button say, to scroll up to the next higher number value the led number choices do not jump one at a time, but "run away" to a number value that you never intended to input.

Meter is pictured here. Idas as to how to fix this? If I cannot do this I am am happy to consider sending it away to an expert repair guy.
 

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Bluejets

Oct 5, 2014
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These things are not made to be repaired so I'm certain if you think you'll get it fixed by "sending it away" you will be disappointed.
Once upon a time (fifty years ago) items like this were made with discrete components but this is no longer done, usually just the one internal chip.
Buy a new one, after all 2017...........
 

Martaine2005

May 12, 2015
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As much as I admire @Bluejets contribution, sometimes it’s not the answer!.
If you have time and the patience, it can SOMETIMES be repaired. A blob (black potting) chip, forget it or reverse engineer.
 

Bluejets

Oct 5, 2014
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Just face the fact..........as in #2
Either that or rub it with a magic mushroom.
 

noquacks

Jun 26, 2013
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As much as I admire @Bluejets contribution, sometimes it’s not the answer!.
If you have time and the patience, it can SOMETIMES be repaired. A blob (black potting) chip, forget it or reverse engineer.

Should I gently try to remove the pad? With a butter knife and see? The meter is pricey, and dont want to ruin the entire thing. I WILL be careful though.......
 

Harald Kapp

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The keypad is very likely of the same kind used in TV remote controls: A PCB with interlaced traces aka fingers and a rubber/silicone dome above each "key" with a conductive coat which, when the "key" is pressed, connects the fingers.

A common issue with this kind of contacts is loss of the conductive coating in which case the key will not react to being pressed. For this kind of failure you can buy a remote control repair kit (example). I have used such a kit successfully in the past.

The failure mode in your case seems to be different. The key makes multiple contacts or activates automatic scrolling of the numbers through a permanent contact. This may be due to pollution of the contact surfaces (on the pcb and/or in the rubber dome). If you manage to open the case of the meter carefully without destruction, you may be able to clean these surfaces with alcohol and a soft cloth or similar. If you find that the conductive coating in the rubber dome has failed, you can then still grab one of the repair kits.
Do not try to pry the rubber dome lose. Usually you can get at the relevant parts when you open the case and disassemble the meter. Srews should be on the back of the case. Or pry open the case when it is made of snap-connected halves.

Note that after opening the meter you will have to calibrate it:
1715082579399.png
 

noquacks

Jun 26, 2013
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The keypad is very likely of the same kind used in TV remote controls: A PCB with interlaced traces aka fingers and a rubber/silicone dome above each "key" with a conductive coat which, when the "key" is pressed, connects the fingers.

A common issue with this kind of contacts is loss of the conductive coating in which case the key will not react to being pressed. For this kind of failure you can buy a remote control repair kit (example). I have used such a kit successfully in the past.

The failure mode in your case seems to be different. The key makes multiple contacts or activates automatic scrolling of the numbers through a permanent contact. This may be due to pollution of the contact surfaces (on the pcb and/or in the rubber dome). If you manage to open the case of the meter carefully without destruction, you may be able to clean these surfaces with alcohol and a soft cloth or similar. If you find that the conductive coating in the rubber dome has failed, you can then still grab one of the repair kits.
Do not try to pry the rubber dome lose. Usually you can get at the relevant parts when you open the case and disassemble the meter. Srews should be on the back of the case. Or pry open the case when it is made of snap-connected halves.

Note that after opening the meter you will have to calibrate it:
View attachment 63542

Wow, for 42 euros I can get this remote delivered? If so, I am ready to try this out. I figure, low risk, compared to the cost of new pH meter. I would rather try this than trying to take apart the unit, and maybe damage something.

If I order this unit do I have to program it? Is it ready to use on a pH meter?
 

Bluejets

Oct 5, 2014
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Pretty sure you missed #7 point.....try reading it again.
Halold also made the point about "multiple switching" or contact bounce" which would be inaccessible to fix/access in a modern day design.
 

noquacks

Jun 26, 2013
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Thanks for clarifying, people. Easy for a novice to misunderstand what's being conveyed, I guess. No easy fix for this meter.
 

Bluejets

Oct 5, 2014
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Thanks for clarifying, people. Easy for a novice to misunderstand what's being conveyed, I guess. No easy fix for this meter.
If you or one of your mates is proficient with soldering etc. you might like to try adding a small twin cable across the on-board contact for the operation in question, bring out to the outer case and add a single small push button tactile switch.
It is possible to get these tactile switches in "modules" also, any number from 2 up to the one shown below.
That is if you think other pushbuttons may also fail which is on the cards.
 

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