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Interesting Power Supply Issue

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Journey11

May 23, 2018
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Hi All,
Been a while ...
I have an interesting issue with a washing machine motor control board. The washer works as in going through the cycle but motor won't spin. In rush current thermistor decided to unsolder itself from the pcb. Owner resoldered and it ran for 12 loads and then burned itself out. Some other repair idiot just jumped it and it wouldn't work. After I got hold of it ... I found a cap that was sploded.
So replaced Cap and Thermistor and tested ... no go ... then decided to draw schematic and during that process found broken solder joint at R75 in included partial schematic. Broken conn was on side of R75 that supplies 160V to Q10 and Q9. Once that was fixed everything seemed to be fine. I decided to take one more voltage measurement at Q9 pin 1 and Q10 popped it's lid. (????)
I ordered 4 KSP44's ( a slightly beefier unit than original KSP42 ) ... replaced blown Q10 and also replaced Q9 as well just in case. Hooked up AC and nothing ... no smoke and no voltage on zeners. Found that both zeners were blown ... D11 shorted and the other (D10) crippled. Replaced both and retested ... this time all 3 transistors blew in a blaze of sparks. ( WTF I thot ? )
So when looking at the damage ...I found D8 had been blown apart.

So here's my question ... if D8 was open ( tested/measured was open ) ... would that have caused all 3 transistors to pop off ? My thinking is that the answer would be YES ...
Any thought out there ?
I have found a reasonable replacement for D8 and had extra Q's for 8,9, and 10 ... Q8 is now the old Q9 I decided to swap out. I just have to replace the zeners again and ready to test again but wanted to get some input here on it.View attachment 55592

I am just about ready to retest ... just need to replace zeners again. I must have powered that brd up at least ten times taking all the shown voltages on the scheme.
All voltages shown were taken after R75 was repaired and since I went thru all the trouble to do the scheme and take some measurements to make it better I wanted one more reading at Q9 pin 1 ... all hell broke loose.
The old Q9 is now Q8 which still tests ok ... had ordered extras for KSP44's so good to go for a retest but want some feed back.
The brd part number is 134393900 for a Kenmore 417.44042400 front loader washing machine ... I have a full schematic drawn up for it.
 
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Harald Kapp

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Nov 17, 2011
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The schematic is in this thread.
I'll close this one here as it is a doublette of the other thread (but missing the schematic ).
 
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