Heat Pump repair (outdoor pcb, mhi)

[HackedFridgeMagnet]

Hi
Just at the end of winter my heat pump failed. SRK71ZRA-W. Just stopped working, it may have been a bit stormy but I didn't notice any strikes nearby.
It had been running for 6 months happily but I can't seen to organise warranty, unhappily.
Two cascaded breakers had been tripped. 32 amp and a 20 amp.
After reset the error lights started messaging. Green run LED 5 flashes, yellow timer LED  always on. This decodes to

green 5-time flash: yellow ON:  outdoor 2-time flash:  E 47 Active filter voltage error:  Defective active filter:  When the wrong voltage connected for the power supply. When the outdoor PCB is faulty.

Thought i might document my attempted repair.
https://mhiaa.com.au/document/service-support-handbook/

[HackedFridgeMagnet]

So opened up the outdoor unit an checked every fuse i can find.
found 4, F1, F3, F4, F8 all were good. Circuit breakers must have broken first.

They have a nice little block diagram inside the outdoor unit.

On the diagram it seems one of the PAM circuits for PFC has failed.

There is a relay before the recitifier which now no longer turns on, so the fault is detected before it trips the breaker again.

[HackedFridgeMagnet]

some photos

[HackedFridgeMagnet]

I have found a short on an IGBT. and have removed it.
Single sided board, in an enclosure that seems to give good access to ants and a moth that died.
Conformal coated.

there are two parrallel active filters, but only one has failed. They consist of a boost converter driven by apparently a PAM algorithm.
10mH inductor, shorting switch (igbt) series switch (diode) and caps.

the igbt is marked KGF 50N60KDA is driven by TLP351H,

i have ordered IKWH60N65WR6XKSA1 to replace at AU$7 each. Hopefully it is equivalent.

[HackedFridgeMagnet]

I was wonder what would happen if I just disconnected one of the Active filters ( the failed one) or both?
But anyway I have a probable fix (i hope) which I will try first.

[HackedFridgeMagnet]

Annotated the pcb for those interested.

[ace1903]

Could you please pictures of the inductors?
Usually I see iron core inductors and that makes me wonder what the operating frequency is.

[HackedFridgeMagnet]

When i reassemble I will take a picture.
I assume they are steel core, Im fairly sure I saw laminations but wasn't paying attention.

 

[xavier60]

Possible Gate driver damage should be checked for. Assuming 2 separate drivers, Digital multimeter resistance and diode type comparisons can be made.

[HackedFridgeMagnet]

Here is one of the 10mH inductors.
Looks like silicon steel.
I am not sure on the pfc frequency but im pretty sure it is 20khz to 100khz and im guessing probably around 25khz.
I am not sure how well these work at DC and at these frequencies but i'm guessing its a pretty standard component.

[wraper]

I have found a short on an IGBT. and have removed it.
Single sided board, in an enclosure that seems to give good access to ants and a moth that died.
Conformal coated.

Looks like flux residues from wave soldering.

[HackedFridgeMagnet]

Yeah good call on the gate drive. I was concerned about it.
Once I had remove the IGBT then both gate drives exhibited the same resistances in every place i could test. So I assumed it was good.
I did further unpowered testing of all the other components nearby in the circuit. All good.
My IGBTs arrived Friday and the unit is all back together now.

I ran the heat pump last night and it worked fine. Yay.

[HackedFridgeMagnet]

It definitely was conformal coated. When I unscrewed the bolts for the heatsink it lifted up a waterproof film with the bolt.
Also had to pierce the coating to take any measurements.

Probably flux residue too.

[johansen]

Some of these thing use a much lower frequency for CCM boost conversion, i have seen iron cored pfc inductors in a number of them.
The high frequency drives can fit a 3 ton system through 2, inductors about 7cm outer diameter and 3 thick. That's the finished dimensions of the toroidal inductor.

I have 2, 5 ton boards and the two inductors are Krispy creme donut sized.

[HackedFridgeMagnet]

Interesting that they go lower than audio frequencies.
I never suspected they would, but I don't just know much about applied magnetics.
I wonder what frequency the do use then.
I guess they also multiphase the two switches too.