Help needed in repairing Sonos Connect - ZP90 (power board) after power surge

Thread Starter

hafren

Joined Mar 1, 2019
28
I am very much a novice in electronic repair but am keen to learn but I’ve drawn a blank in fixing my Sonos connect so looking for help. After removing the power board I could tell the fuse had blown and a NTC thermistor had failed. I also suspected capacitor C206 (1800uF, 6.3V) which appeared to have bulged top. I do not see any other signs of distress so I replaced all of these components and upon power up the fuse immediately blew.

So there is clearly something wrong/shorted downstream of the earlier failed parts thermistor & fuse and need some advice what I can check. I have searched unsuccessfully to find schematics but have read many other posters that have successfully repaired their Sonos connect after a power surge. Most others were successful in replacing the exact same components I’ve replaced so what I can check next? Pictures of my power board are attached.
 

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narkeleptk

Joined Mar 11, 2019
367
Hard to see much from photos and I do not know power supplys well but you could check that so-8 IC there for a short and check those diodes. If they are ok its probably the transformer. Maybe one of the guys who know power supplys will chime in and lead you a little better.
 
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Dodgydave

Joined Jun 22, 2012
8,359
It's a switchmode psu, and it's probably blown the chip (pins 1, 2 shorted) fuse, thermistor, on the output is just a diode, capacitor and opto-coupler and TL431 zener for regulation.

This is the chip and a typical circuit diagram...2cx86zd.png
 
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Thread Starter

hafren

Joined Mar 1, 2019
28
It's a switchmode psu, and it's probably blown the chip (pins 1, 2 shorted)
I checked the chip, Fairchild 5M0165R, for shorts across pins; 1/6/7/8 (drain) to 2 (GND) & is open circuit. I looks difficult but not impossible to desolder from board but if its open circuit does that indicate its not the problem source? I'm going to make a dim bulb tester to see if I can run the circuit without blowing the fuse and see if I can detect any components getting hot? Any other advise on what I can do/check?
 

Dodgydave

Joined Jun 22, 2012
8,359
All i can suggest is replace the mosfet, chip, and check any other silicon parts D2, looks like you have removed a few ...
 
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LesJones

Joined Jan 8, 2017
2,316
The bridge rectifier is also another possible cause for blowing fuses. Check that none of the 4 diodes in the bridge rectifier are shorted.

Les.
 

Thread Starter

hafren

Joined Mar 1, 2019
28
The bridge rectifier is also another possible cause for blowing fuses. Check that none of the 4 diodes in the bridge rectifier are shorted.

Les.
Yep just tested MB8S bridge rectifier and its shorted. Thanks.
 

Ylli

Joined Nov 13, 2015
764
Need to be careful using a DBT or other limiter or soft start when testing a SMPS. One of the features of a SMPS is that if the input voltage is low, it will just draw more current to supply the needed output. It is effectively a negative resistance. As such it can be made to oscillate quite easily if you try to moderate the input current/voltage.
 
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