Washing machine PCB power supply fault

Thread Starter

Copey84

Joined Jul 27, 2015
198
Hello, this morning my washing machine decided to give up so ive had a go at trying to fix it.
Took awhile but I think I've found the fault in the power supply to the main PCB.
Thought the fault was in the transformer as that's where I think heat had started, no major damage just some blackening around it and other components.
Removed the transformer expecting to see further damage in coil but seemed ok, starting to think the transformer heated up due to increase in voltage.
Have included pic of power supply, mains voltage at 240v goes across the green power resistor, not sure what yellow component is, then there's two 4007 diodes in series with each other. Measured the voltage at mid point of diodes an I got 108v DC, seems ok as it's half the sine wave. The voltage then increases to 338v DC across the second diode, this was present at transformer.
Could it be the high DC voltage that's to blame for heat at transformer, or have I missed something?
Don't fully understand how the power supply works hoping someone could explain what's going on. Seems strange having a DC voltage going to a transformer.
And how has the DC voltage risen from 108v at centre of diodes to 338v at end of second diode?
As always appreciate any replies.1482865251411102951414.jpg 1482865341057-1811811937.jpg 14828654021681472714319.jpg
 

SLK001

Joined Nov 29, 2011
1,548
Your pictures didn't come thru. If you are getting 300+V on the hot side, then you have a PFC circuit. This is normal. You don't have a DC voltage going to the transformer, but a series of HF pulses. This, too, is normal. Your starting point should be measurements of the OUTPUT voltages to see if they are correct. If they are, your problem lies elsewhere.
 

Thread Starter

Copey84

Joined Jul 27, 2015
198
Hi dodgydave, the second pic shows where transformer was. You can see four pins on the white PCB where it was connected. The two diodes are on right handside of pic.
There was no voltage on secondary side of transformer, and 338v DC on primary. Thought it was faulty so removed it.
Will try and post better pics
 

Thread Starter

Copey84

Joined Jul 27, 2015
198
Thanks max, does this type of ic create a switch mode power supply?
Do you think I could get a replacement transformer for this PCB?
Or could I just add a separate power supply to power PCB? And bypass the existing power supply components.
 

Thread Starter

Copey84

Joined Jul 27, 2015
198
Transformer didnt want to free it's self from board, think it's where fault started, open circuit on one of the windings so no good anyway, in bin now.
Need to figure out if I can replace it or add in a new power supply.
 

MaxHeadRoom

Joined Jul 18, 2013
23,362
Thanks max, does this type of ic create a switch mode power supply?
Do you think I could get a replacement transformer for this PCB?
.
Yes SMPS, and I doubt any luck getting an OEM part.
If you know the output voltage, you may be successful in shoe-horning a sub in place, either DIY or there are several compact switching isolated supplies available.
Max.
 

Thread Starter

Copey84

Joined Jul 27, 2015
198
Thanks max, think I'll try a separate smps.
There is two tracks onto the white PCB and two off, think I can do away with the white PCB and solder my new supply onto the out going tracks, will feed new supply from board.
Traced relays that are on the board of internet, there 12v so will match supply to them.
Sounds a bit dodgy but worth a go, washing machine s aren't cheap.
If you can think of anything else let me know, I'll post how I get on, thanks again.
 

Thread Starter

Copey84

Joined Jul 27, 2015
198
Is a wall wart like a phone charger or similar plug in smps device, I'm in UK not familiar.
Gona go for 12v Dave, there's 5 relays on board probably not all on together but ive allowed 100ma each so half amp supply will cover it.
 

Thread Starter

Copey84

Joined Jul 27, 2015
198
Hello again, tried the smps and although it brought the front console back to life when I tried to run the machine it could only fill with water and would not spin, think the fault has scrambled the machines memory.
Only other option is to try and source the module of internet, but could take awhile to get it and no guarantee it will work. Washing is piling up so looking more likely to be a new machine, a well least the sales have started might get one bit cheaper.
Anyway thanks for replies and happy new year.
 
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