Fridge compressor inverter board with blown LNK304

[shamooooot]

hello

I have a problem in a Beko fridge and I checked the compressor inverter board and I found out the big 220uf/400v cap and the LNK304DN ic were blown.

I looked locally for the ic but I can't find it anywhere and I was wondering if I can do some tweaks to bypass it and run the fridge ASAP, like adding an external 12v power supply to the output or so.

Please let me know what you guys think.

[xavier60]

I guess you can so long as you are aware of the risks. The output of the 12V PSU will become live.
After being sent fake LNK ICs for a blender, I used the internal parts from a 12V regulated plug Pak to get it working. I mounted the parts inside the blender.
Are you certain that it needs 12V?

[DavidAlfa]

You can figure out the output voltage by checking the feedback resistors.
Following the attached picture, it will be aproximately:
1.65 * (1+(R1/R3))

[shamooooot]

so...

The correct voltage should've been 15V on the output so I fed a 12V from an external power supply after Desoldering the LNK304, and connected it to the output cap:



And once I powered the board the microcontroller and the this IC smoked (almost caught on fire):



Did I do something wrong here !

[DavidAlfa]

Did you check the polarity? It's a silly but easy mistake!
Anyways your board is now definitely fried, maybe they were already cooked by the LNK304 failure.
Being a buck design, if the switching transistor shorts out it'll feed ~150V to the output, or ~320V in 220V countries!

[Twoflower]

Not sure you should double-check if the solder joints are OK. The one in the attached picture looks not good. Also the solder joints between the diodes should be checked.

[james_s]

Domestic fridge compressors are using inverters now? The look of that board with its obvious signs of heat damage and cheap electrolytic capacitors does not give me high confidence in long lifespan.

[shamooooot]

Did you check the polarity? It's a silly but easy mistake!
Anyways your board is now definitely fried, maybe they were already cooked by the LNK304 failure.
Being a buck design, if the switching transistor shorts out it'll feed ~150V to the output, or ~320V in 220V countries!

That's exactly what I was thinking of !

Thank you for your help David..

[shamooooot]

Not sure you should double-check if the solder joints are OK. The one in the attached picture looks not good. Also the solder joints between the diodes should be checked.

This joint is for the 3 phase output to the compressor, so I don't know if it can cause any issues..

[DavidAlfa]

It's easy to notice a lack of decent input protection in domestic boards.
They used to place heavy filters, VDRs, PTCs, so on a huge peak the fuse burned, minimizing the damage.

[shamooooot]

Domestic fridge compressors are using inverters now? The look of that board with its obvious signs of heat damage and cheap electrolytic capacitors does not give me high confidence in long lifespan.

Man tell me about it, they are all inverter driven now.. And exactly like you said they use cheap knockoff parts (especially caps) in their boards. It is not the first time I find exploded caps in this board.

I won't ever buy Beko again after seeing this..

[amyk]

Another one of those shitty single-chip SMPSs... they're notorious for self-destructing like that. My theory is that they're very sensitive to power surges.

Domestic fridge compressors are using inverters now? The look of that board with its obvious signs of heat damage and cheap electrolytic capacitors does not give me high confidence in long lifespan.

Planned obsolescence. Hermetic systems can last a century. Unfortunately the compressor might not be the type that can be converted to a classic start relay.

Edit: a week ago someone else had same problem with LNK304: https://www.eevblog.com/forum/repair/zanussi-dryer-blew-lnk304-twice!/