Malfunctioning PCB for Koppel A/C keeps turning unit on and off by itself...

Thread Starter

shaggy77

Joined Sep 23, 2020
6
The broken PCB is the small one on the front of the A/C which accepts input from the infrared remote control.
It also has a physical power button on this PCB which turns the unit on and off with no options.
From the display output on the LED number display on this PCB, it shows the same two lines that would show up if I pushed the physical power button on the PCB.
So my guess is that this manual on/off from the physical button on the PCB is what is getting triggered.
In the middle of the day or the middle of the night, it will act up with a lot of loud beeps and the aircon turning on and off and on and off very fast and it won't stop until I flip the breaker to cut the power.
Then sometimes it will go for several weeks or months with no problem, then it will start again.
I have tried cleaning the contacts of the connectors and it seemed to stop the problem temporarily but it always comes back and it might have only been a coincidence that it worked.
I attached photos of the front and back of the PCB in hopes someone might spot something that might help me fix it.
I have limited electrical knowledge/experience, and I don't have a multimeter or a soldering iron so..... yeah. :(
Thank you.
(higher resolution photo of the board is here: https://www.yogile.com/koppelacpcb)

koppel_ac_pcb_sm.png
 

Irving

Joined Jan 30, 2016
1,020
Hard to say from that view - need to reverse engineer the circuit to see how it works... can you give the part number for the IC (IC1), without that its going to be hard to figure (it might be a custom part though...).
 

Thread Starter

shaggy77

Joined Sep 23, 2020
6
I'm sorry I wasn't able to get the part number.
However, I have another clue to what might be causing the problem, not sure if it helps:
I noticed that after the problem occurred again, and I disconnected the PCB, I still felt a charge when my finger touched the wires on the back of the emergency on/off button or the "manual on/off from the physical button on the PCB" as I called it in my original post.
So I was wondering why I was getting small electric shock from that switch when no electrcity source was attached to it.
Maybe that's the problem?
pcb_shocks.jpg
 
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Wolframore

Joined Jan 21, 2019
1,797
IC1 looks like a TI chip, please identify or post a picture of the chip we can read. You may be getting a small zap from a capacitor. Doesn’t necessarily mean anything is wrong. Nothing looks physically damaged. I wonder if you have a bad/worn out switch.
 

Thread Starter

shaggy77

Joined Sep 23, 2020
6
While you’re focusing on the remote unit do you realize the fault could be on the main board?
It could be, but I live in SE Asia and we use A/C every night, and cannot afford right now to buy a new one, so I have been dealing with the problem by turning on the A/C, setting the temp with the remote, and then unplugging the PCB for the remote from the main board and leaving it disconnected thru the night until I want to turn it off the A/C in the morning, then I connect it again, use the remote to turn off the A/C, and shut off the breaker so that it doesn't randomly turn on and off during the day. The aircon runs fine while the remote PCB is disconnected and maintains the temp set before I disconnected it.
 

Thread Starter

shaggy77

Joined Sep 23, 2020
6
Do you have a TV near this unit? Stray infra red from another remote could trigger it, try putting something over the IR sensor to rule this out.
No tv or other infrared device, there is no chance of stray infrared triggering it. And the problem occurs in the middle of the night sometimes in total darkness. I'm pretty sure there is a short in the PCB for the remote. It seems to me that the emergency/manual on/off button/switch whatever-u-call-it (S201) gets overloaded with electrical charge if it stays plugged in for too long and then starts behaving erratically. That's just my feeling or intuition about it. I'm not sure. The display switches to the output that is shown when the manual on/off button is pressed and the A/C behaves as if that button is being pressed again and again very fast.
 
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