Connect ZP90 No Power Repair

  • 6 February 2019
  • 6 replies
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Userlevel 1
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I just spent some time with a ZP90 that would not power on.
Mine did not have the fuse blown, and the PWM IC appeared to be switching but it was bursting on and off.
That is where the onion began, the more I peeled the more I cried.
It has a very simple power supply. It has just a 2 output fly-back with second stage LC filters on each of the 2 outputs (3.3V, 12ishV). Which means there are 2 electrolytic caps on each output and 1 on the housekeeping voltage output. So if you're playing at home, that is a total of 5 output caps. Of my 5, 3 had a huge ESR. Which means they failed.
First i replaced the housekeeping winding electrolytic, and the bursting largely stopped but there was still a weird oscillation happening on both outputs. So after scratching my head for a while I checked the output caps and found that most of them were bad too. What happens with 2 stage filters is that if one of the C value changes in either stage, they can start to act on each other and oscillatory behavior can begin. ON the 12V output the oscillations dipped below 12V and the LDO on the analog board quits and you get no analog output even though the controller works as expected in terms of the Sonos app.

6 replies

Userlevel 7
Badge +18
Hi, gruv2ths. Unfortunately I am unable to advise as to how to do a DIY repair on a speaker. I'm sorry to storm in on your thread but I just wanted to place a disclaimer for anyone reading along, that should a device be tampered with, we will be unable to honour any warranty claims. Thank you and best of luck.
Could you help with advice fixing my power surged ZP90. I’ve hit a hurdle 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 else wrong besides these parts and need some advice what else I can check

Forum apologies for the other post.
Userlevel 1
Badge +2
Hey Dyfi,
So you still have a short if you are still blowing fuses.
While you are in there I would replace ALL electrolytic caps. Any one of them will cause your Connect to not work if their ESR is too high. Most of mine were at least 2x higher than the parts spec.
The one to be very careful with is the small one by the PWM chip. (the PWM's bias winding cap) The reason is because it connects on the top of the board and the bottom. This cap has caused me so much stress. Be sure that when the cap is removed that the via that the caps leads leads go through have continuity top to bottom. When the cap is replaced, and the board does not work, you can not see the voltage under the new part. What ends up happening is, you see Vbias on the PWM and it is charging and discharging at a different rate as the power supply's output caps. That's the give away.
The caps on this board are problematic, so do yourself a favor and replace them all.

Anyway, chances are you fuse blower is the PWM. The PWM on this board has an integrated switching FET that is probably shorted. Try removing the PWM (DIP8 i believe) and see if your fuse blows again. You can probably just cut the pins of the part and lift the body out. Pins come out easier one by one if they are not connected to the body.

Let us know how it goes.
After extremely annoying cutouts with one of my ZP90s (wired Ethernet connected, no issues in app), I concluded it was an analog stage issue. Opened it up (well out of warranty) and discovered the same bulging power caps on the small power PCB gruv2ths mentions. Replaced the 2 caps that appeared bad (an 1800uf 6.4v and a 100uf 25v) but to no avail. Unit functions as before with audio cutouts that make it unusable. Contemplated just getting another one, but hesitant to shell out $360 for another identically flawed PS design. By comparison my Denon amp that it's connected to has been running strong for 20 years and it's the one I would have expected to have issues given it's the one with the power transistors. The ZP90 just has to supply line-level output and failed. Kind of disappointing.
Userlevel 1
Badge +2
I would replace all of the electrolytic caps. All of mine had high ESR, and most looked like new.
Thanks, I'll give that a shot.

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