Wondering if someone can help.

I have a Klarstein cooler that has two TECs. Until recently the cooler was working fine, then out of the blue it started massively overshooting the set point. For example, the ambient is currently 19c but the internal temp is 12c despite the set point being 18c. I have another two of the same cooler all next to each other and they work fine.

I took the back off and could hear some chirping noises and the red and green LEDs flicker a bit. The board is a FX-100 2A (PCB91123F3). It looks the same as many boards posted here but has outputs for two TECs.

I found replacement board but it’s almost as much as I paid for the whole cooler…I’m happy to try and replace any components on the board but wonder if anyone has any idea about what might be the issue? Most people I see here have the opposite issue that the coolers don’t work but mine seem to be running way beyond where they should be. Could a capacitor like C8 cause this?

thanks!

 

Not likely C8. You want to look at the thermistor cabling and assembly.

 

Agreed. Since it's cooling, the power is fine but the control circuitry has a problem.

Note however that if you do end up ordering parts, get some spare capacitors included in your order. They cost next to nothing and are like insurance for these things.

 

Thanks for the advice. The temp reading on the display at the front and additional external temperature sensors all read the same. If I put my finger on the thermistor the temperature increased on the display readout.

Cabling looks absolutely fine. It’s so strange that it cools to pretty much 12c exactly. It’s like it’s failing to properly control the TECs and they’re running at full power.

What might the chirping noises and inconsistent LED flickers suggest is happening?

 

If I put my finger on the thermistor the temperature increased on the display readout.

Well done.

Good questions, and I'm afraid I don't know the answers. Replacing the board might be the next best option. You could try the shotgun approach and just replace all the caps, but I'm a little skeptical that would do it.

You can find schematics for these boards here in this forum. The transistors that control power to the TECs might have failed "on". If you have the chops to trace out the control scheme, identify the base (or gate) of the transistors and check the voltage there. Are they on despite being told to be off?

 

This is the temperature control circuit.
If you are able, look at the voltage coming from pin-1 and pin-7 of the LM358 as you warm up the thermistor.
Connecting to one of the resistors or diodes is safer than trying to probe the IC pins.

If you can post a sharp closeup of the board we will be able to guide you.

 

I’ve just found a post on this forum of someone saying theirs is stuck at 12c regardless of SP and changing C8 fixed it. I’ve ordered new caps for the whole board and I’ll move into mosfets etc after. Hoping that solves it as I don’t have access to the testing equipment atm.

thanks for all the pointers

 

Wondering if someone can help.

I have a Klarstein cooler that has two TECs. Until recently the cooler was working fine, then out of the blue it started massively overshooting the set point. For example, the ambient is currently 19c but the internal temp is 12c despite the set point being 18c. I have another two of the same cooler all next to each other and they work fine.

I took the back off and could hear some chirping noises and the red and green LEDs flicker a bit. The board is a FX-100 2A (PCB91123F3). It looks the same as many boards posted here but has outputs for two TECs.

I found replacement board but it’s almost as much as I paid for the whole cooler…I’m happy to try and replace any components on the board but wonder if anyone has any idea about what might be the issue? Most people I see here have the opposite issue that the coolers don’t work but mine seem to be running way beyond where they should be. Could a capacitor like C8 cause this?

thanks!

I hope this helps my repair costs were $16.17 + shipping & I only used an ohm meter.

 

I hope this helps my repair costs were $16.17 + shipping & I only used an ohm meter.

Thank you - in the end I binned the whole board and designed my own which is on the way to me now. Gives me more control over the peltiers, adds heating (since I use this as a humidor) and enables me to write a better algorithm for my use case.

thanks for all the help.

Josh

 

I hope this helps my repair costs were $16.17 + shipping & I only used an ohm meter.

Nice. Have you posted your results in the Success thread? It may help others there.

https://forum.allaboutcircuits.com/threads/success-stories-repair-thermoelectric-cooler.101748/