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.
All the voltages shown on schematic were taken after I found and fixed broken solder joint at R75 and pins 1 and 3 Of Q10 and Q9. Again all I did was try to see what the voltage was on pin 1 of Q9 and all hell broke loose. I must have powered that brd up at least ten times to take what voltage measurements are shown and no issues.
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.

All the voltages shown on schematic were taken after I found and fixed broken solder joint at R75 and pins 1 and 3 Of Q10 and Q9. Again all I did was try to see what the voltage was on pin 1 of Q9 and all hell broke loose. I must have powered that brd up at least ten times to take what voltage measurements are shown and no issues.
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