Repair ZP120

Also there doesn’t seem to be anything visually to indicate component failure such a as burns or broken areas

Yes, the inductors may appear to as shorts if they are used with dual windings for filtering... same concept as the transformer. Also, chances are that your transformers and inductors are ok. Those are really really hard to blow. Concentrate on diodes/caps/resistors/ICs.

Small tip: If your components look good... put them back in. Its easy to lose the correct ones. If you want to leave off inductors and transformers, then thats fine.

Second small tip: Test what you can on-board/in-circuit. If it looks good, you can likely not worry about removing it. If it looks bad, then you can do a secondary test after removing it. That may prevent having to remove a lot.

Well I have checked everything I can think of in or near the part of the circuit that has the short. Seems like all caps and resistors check out OK. My guess is that the STA508 amp chip may be shorted and that is what is causing the failure. I cannot think of anything else unless you guys can.

Great work!
So this is what I was hoping was not the culprit. But all is not lost if it is, I have replaced both of these on a repair once. I will tell you the easy way to get these off if need be. Found them on eBay from a stateside seller. Lots of the pins on the one side are supposed to be shorted together, but not all.. LOL
This I have found to be very very close to how Sonos has implemented the STA508.
http://www.st.com/resource/en/datasheet/sta508.pdf See Figure 7 on page 7.

m0untainman and I both have removed that same common mode choke, it separates the 36V power supply from the load.
So you can narrow down where your short is. We both had a rough time getting it back in. :-)

I would have given you the same advice that m0untainman did above, 'it probably aint the magnetics'!
Well guess what, I fixed one this weekend that had both of the windings of the common mode choke in the input filter (right after the diode bridge) blown open. Consequently the of the big storage caps threw up under it's top cap. Strangely there were no shorts and the fuse was not blown.

Thanks gruv2ths - I did try removing the STA508 with Chip Quick but I could not get it off for some reason. A friend of mine has some better tools so I am going to take it to him to see if he can remove it. Also do you have a link for that eBay seller for the STA508? The only one I found is from China and the ETA is about 2-3 weeks. Would like to get it sooner if possible.

As for any other visible sign of a short, there does not seem to be anything. I have closely looked at all the caps, inductors and resistors and they look absolutely perfect. I am hoping that the STA508 is the root cause of the fail and replacing it will bring this baby to life!

So what I do just requires a small flat screwdriver and your soldering iron.
All I do is solder all of the pins together on the side you want to remove. Then once there is a lot of solder across all of the pins keep moving your iron back and forth across all of the pins, the idea is to get all of the pins molten at the same time. Once you are liquid pretty much all the way across gently pry up the chip on the side with the solder. You will bend the leads on the side you have not touched. Then repeat on the other side.
FYI i lifted the pad from pin 18 on both the ones I replaced. But it is a no connect pin so no harm no foul.

Well I got the STA508 removed and the short has disappeared! I am hoping that this is the cause of the failure. I found a US seller on eBay and wanted your opinion to see if this is the same part: https://www.ebay.com/itm/121059786762?ul_noapp=true

After PMing gruv2ths, I am going to try putting the amp back together and powering it up with the STA508 removed. He said it should power on without it if there are no other issues with the amp. I will update this thread later today with my findings!

Wish me luck and fingers crossed!

So if you are getting 3.3,5 and 15 then your bias converter is working. You are not seeing voltages at the transformer because it is a AC signal and your meter is probably in DC mode. As long as you are getting the voltages above your bias converter is fine. Let’s let that go. Are the RTN pins 0 ohms on the transformer secondary? I believe they are the 1st and 3rd pins from the left.
Dumb question but is the gray ribbon connected from the login board to the led/button assembly?
Also what happens if you plug in a active Ethernet cable to the back? Any network activity?