Carrier HK50AA063 display controller common failure help

[ctroxtell]

I've got a control display for a Carrier chiller that I'm trying to understand what the common failure with these boards are. This is the board in question https://www.supplyhouse.com/Carrier-...arquee-Display all of them seem to develop a failure with the up and down arrow buttons on the right side of the display, the esc and enter keys I've never seen fail. Once these boards are plugged in they run 24/7, you used to have to press extremely hard with the end of the blunt screwdriver and you could still get the arrows to work but now it has completely stopped working. The button that contacts the board is a rubber with a waffle looking pattern. I will add photos of this, just hoping someone can help me understand what may be happening.

[sam_sam_sam]

These are known as membrane key pads and they are notoriously difficult to replace if not impossible to repair because they are incapacitated between several layers of some kind a flexible plastic what I call a metal bubble switch contacts and if push to hard they collapse and are then useless after that

If you can figure out switch pins outs you might be able use external switches in there places but this sometimes very tricky and time consuming endeavor or try ito find a non working one and hope that the touch pads are still working properly

These devices are very priority and you will not get technical assistance for them at all and you will not be able find replacement parts for them either with out going through Carrier corporation these devices are known as building management systems I use to work at places that Train building management systems and they had a similar device and the touch pads would eventually get so bad they would have to replace them but this company that worked for had a service contract with them so we did not have to deal with this part of it

This device is not exactly same setup that I am used to I used to the system that is completely connected to something that is very similar to a CNC machine controller but it is different in that it controls individual rooms air damper system and temperature control and the chiller controls system they are all tied together in one place and you access the site management system to control everything

[ctroxtell]

These are known as membrane key pads and they are notoriously difficult to replace if not impossible to repair because they are incapacitated between several layers of some kind a flexible plastic what I call a metal bubble switch contacts and if push to hard they collapse and are then useless after that

If you can figure out switch pins outs you might be able use external switches in there places but this sometimes very tricky and time consuming endeavor or try ito find a non working one and hope that the touch pads are still working properly

These devices are very priority and you will not get technical assistance for them at all and you will not be able find replacement parts for them either with out going through Carrier corporation these devices are known as building management systems I use to work at places that Train building management systems and they had a similar device and the touch pads would eventually get so bad they would have to replace them but this company that worked for had a service contract with them so we did not have to deal with this part of it

This device is not exactly same setup that I am used to I used to the system that is completely connected to something that is very similar to a CNC machine controller but it is different in that it controls individual rooms air damper system and temperature control and the chiller controls system they are all tied together in one place and you access the site management system to control everything

Thank you for that information, as I was talking with another technician today and he was saying it was always the same thing " the up and down arrows stop working and the other two buttons never seem to fail". I thought maybe it was something to do with the board staying powered on 24/7 but it sounds like since these buttons are used more they are always the failed section. I will definitely attempt to work on the board and see if I can perhaps solder an external switch onto it since the membrane pad fails.

[R_J]

The rubber button should have a conductive carbon impregnated in it, after time the button is no longer conductive, try recoating then with a conductive coating. They have remote control contact repair kits available where you can attach new conductive dots
You could try some alcohol to clean the rubber contact and the board but do it lightly or you could remove any carbon left on the button and the printed trace on the pc board
I have repaired many remotes with similar problems. they have ways to do it now, just enter "remote control button repair kit" into google You can use either replacement carbon dots or the have a conductive paint that works.

The up/down buttons only have one contact where the esc/enter use 3 contacts so they would likely last longer.

[ctroxtell]

So I got to digging and found an HVAC tech who got tired of the issues and soldered mechanical tactical microswitches onto the board. He said he's ran into at least one board that the microswitches refused to work. https://www.youtube.com/watch?v=1GOP9kIy2_s useful information though. I tried to wet the tip of my finger and touch the pad to simulate a conductor, it worked on the esc and enter keys I think but not on the up and down keys.

[R_J]

Try a jumper wire between the two silver connections on the printed contacts, that should check if the actual input circuit works, and it is the printed switch that is the only fault

[stj]

i have seen a guy fix those rubber pads by using graphite from a soft pencil.
never tried it myself yet though.

[redwire]

What I see is some contamination on the PCB for the upper button S3.
I would clean the board there with a q-tip and IPA, and don't rub the carbon-print too hard either. Let it dry out afterwards.
If the keypad are worn (it's usually just conductive paint they use) you can use a "remote control repair kit' and put new conductive silicone rubber pads on those buttons. "rubber pad kit from fleaBay "keypad repair KIT for IR remote controllers - 100pcs conductive pads 1.5mm~10mm" is what I use; this post #17

But Carrier has a bad design here where they plopped a noisy buck-converter circuit right next to the two button pads. So of course it would pick up noise from that.
I'm wondering if the actual problem is the noise is worse due to aging electrolytic capacitors. The Lelon VEJ series is rated 2,000hrs 105C and some are near parts that make heat.
So I would test some of the board's capacitors to see if they are fading out and this is the real problem- because why do these two keys go bad but the others don't... is a bit weird.