Liebherr 3056 Power board resistor

[plwsm]

Hi,
Abit of a long shot, but does anyone have a power board for a ICBN3056 to hand and can tell me the colour code on the power resistor in the middle of the board please? (or its resistance value)

My 4 year old fridge freezer failed today (completely dead with no display etc.). The fuse was ok. As a retired electronics engineer, I thought I would see if I could repair it (I have ordered a replacement in any case, but it will take a few days to arrive). I tracked the problem down to a 400V 10uF electrolytic capacitor going short which has also taken out the fusible resistor feeding the high voltage circuit. This is the resistor mounted on top of a capacitor near the center of the board. The resistor has discolored and I cannot read the colour of the third band on the part (the bands are brown, black, ?, gold). As it has failed open circuit, I cannot measure the resistance directly.

I think the reason the cap. failed in the first place maybe something to do with my AC mains supply being on the high side (250.5VAC rms). I spoke to my local electricity supplier and they said although the upper limit is 253V (i.e nominal 230V + 10{e5d1b7155a01ef1f3b9c9968eaba33524ee81600d00d4be2b4d93ac2e58cec2d}) they try to keep below 250V and the high reading maybe partly due to a number of houses with solar PV close by being on the same phase .
When the 250VAC rectified, this will give about 354VDC so there is little in the way of derating on the 400V cap. I have replaced it with a 450V part with a much higher reliability of 10,000 hours at 105C (the original part was only 2,000 hours).

Thanks for any assistance you can provide.

[electrofix]

Re: Liebherr 3056 Power board resistor

most of these feed resistors are normally 100 ohms or less. since it is unlikely it will be 10 ohms 100 ohms fusible resistor sounds likely

Dave

[plwsm]

Re: Liebherr 3056 Power board resistor

Thanks Dave. I agree that 100 ohms looks most likely, but I am still a bit apprehensive
since the “brown” third band doesn’t look the same brown as on the first band. I was hoping that someone could confirm either way.
Thanks again for your reply.

Phil

[electrofix]

Re: Liebherr 3056 Power board resistor

dont know the board but going by other examples i think it will be like this

the mains comes in through the 100 ohm resistor get rectified to DC

This voltage is then used by a power supply chip like LNK364pn or TYN278GN or similar which then produces the voltage for the board. the 100 ohm resistor is not used to drop voltage and is purely there as a safety device in case of short circuit. not only will it limit the current but will blow to stop fires. it is possible that the shorted cap may have blown the chip as well so if it pops when you turn on change it

Dave

[plwsm]

Re: Liebherr 3056 Power board resistor

Dave,
It was a 100 ohm fusible resistor after all. I changed this and the failed capacitor and the board (and fridge) are now working fine. The board uses a NCP1051C switching regulator in the power supply and this was still ok.
I understand the importance of using a fusible resistor here for safety reasons as these are guaranteed to fail open circuit when overloaded.
Thanks again for your help.

Phil

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