Repair ZP120

@m0untainman - RE: The caps you mentioned. I think my picture threw off your orientation. See the full sized pic below. Are those the caps you were talking about with the plastic tops?

Yep... you are good. 🙂

A quick update: I ordered the caps and resistors needed to replace the faulty ones. The caps are size 1206 SMD ceramic and I got 2 different values as they are not marked so I guessed (.01uf and .1uf). The resistors are marked with a "750" on them which means they are 75 ohm size 0603 SMD. After ordering the parts, I started to look around closer at the rest of the WiFi board. I took the tops off of the three metal housings on the board and found yet another burned component. This one looks like an inductor inside the metal housing closest to the original failed parts. Judging by the other comonents around it, the circuit seems to be a transceiver circuit for the Ethernet ports. I determined this by looking at the chip with the part number 78Q2123.
When I put my ohm meter on the failed inductor it read .890 M ohms. The size seems to be a 0603, but I will need to figure out the value and order one of these as well. This one is going to be very challenging to replace as it is inside the metal housing that is closest to the faulted caps and resistors. So the story continues. I am going to be really happy if replacing these parts makes this amp functional again!

Yeah... 0V on the secondary side of that PWM is a big red flag that the PWM is bad. On a dim bulb tester is the PWM warm? Since your dim bulb goes dark, I'm guessing its not. So far we have seen a couple of those go sour and the liquid issues that you showed could mean it got wet. It seems to be a pretty sensitive part.

That said, without that part working, you shouldn't have gotten the white light to show any color (at least that was the way it was for me).

Thanks m0untainman,
Yesterday I had some time and on a hunch I replaced the PWM but it did not fix the issue. I am really stumped by this but also determined to understand why it is failing and fix it 🙂 I just sent you and gruv2ths PM's asking about getting some detailed readings and what GND points you used. In some of my first posts I was using chassis as GND and I am not sure if that was correct. I would like to start over fresh and try to troubleshoot the switching power supply to see if it is working properly or not.

Also on the white LED you mentioned above, I have never really gotten the LED to shine brightly, just very (and I mean very) dimly lit.

Hi, can anybody tell me the vale of resistor R15550, located under the WiFi module on the ZP120?

This component is missing on my board ( knocked off and lost by previous “repairer”). Oddly, the player still works, but I would like to replace it.

 

The RTN should be ground (1 and 3)

@gruv2ths - I just read you most recent PM to my questions about where to put the black lead from teh meter when reading voltages on the power supply and below are my readings. As I said before, The only readings that are different from yours are the P-FET and the secondary switching transformer. See below for pictures and explanations.

On another note, while the AMP is plugged in, there seems to be some voltage going to the logic board as I have read 5V across some of the small electrolytic caps. Also some of the chips that are under the metal housing are slightly warm to the touch. Not hot mind you, just slightly warm like you can tell voltage is applied. I am not sure what that means but I thought it was worth noting.

I seem to be a bit lost for why this thing is not working.

Here are the voltage reading pictures:

Also here are some readings from the logic board:

Here’s a similar issue that your info helped me solve (I’m 99% sure)...

Well, no joy - but oh so close…

I ran 4 jumpers where those traces should be (there are four total connections from the small power supply area to the riser - all four jumpers were destroyed.  I replaced the dead resistor too.  I also had to bridge the two grounds on the secondary side.  This is all on top of having already replaced some capacitors, and the two mosfets.

It booted up ok, but when I hit play I still get the white/orange cycle.

The difference this time is that the 36V section of the secondary does ramp up to 36V momentarily after I hit play.  Once the yellow comes on it falls back to 15V.

The real surprise (to me) is that there is only 280V on the primary side of the supply instead of the usual 320V.  That tells me that there is either still something wrong there, or there is some kind of power draw on the secondary side that is preventing the primary from reaching 320V.  I disconnected the 15v/8v section of the secondary and tried again -- this time the primary gets to 306V.  I think that this means the primary isn’t generating enough power to drive the load properly… My logic is that if there was a short on the 3.3V rail, I should still get 280V, and if there was a short on the 15v/5v rails then I should get 320V.

I’ll keep looking but honestly I’ve been through this one pretty thoroughly so don’t know what to look for any more.

 

I have another ZP120 that is now showing similar symptoms (including 280V on the primary) but arrived to its condition via a different route.  That one had a bad transformer primary.  I removed the transformer and found that its winding connections had rusted away.  I was able to get them reconnected, but it was microsurgery and I must have damaged something.  When I reinstalled it, it now boots ok but also goes into the white/yellow cycle when I press play.  I think that the primary winding got shorted and it just isn’t generating enough voltages on the secondaries to make it work.

 

The other possibility for both of these is that the amp chips are fried.  I probably don’t have much to lose to try replacing those at this point.

 

 

Really great documentation here, well done!
Couple of observations.
-if you are getting the 3.3,8ish,15 on the secondary then the bias converter PWM is working correctly.
-The reason you are seeing 0V on the transformers pins is because you are looking at AC with your meter set to DC. Those biases measured in the logic card say to me that the bias converter is running and the output is making its way to the logic card. Good sign
-I can only think of one thing left to do, and that is measure the output of the buck converter on the bottom of the logic card. There is a inductor with a (normally) yellow electrolytic cap. Solder a wire to the striped side of the cap and put the card back in and plug in. You can put the red lead on the wire and the black one to chassis. Should have 1.5V output.

Do you know much about reading serial (UART) from a computer? You may have noticed a 4 pin header under the EMI shield that you removed. There may be some diagnostic clues coming out of that serial headder.

The one I am working currently has a confirmed good power and riser boards and shows up in the Sonos app but when you push play I get orange and white blinking leds. Wanting to read that header and see if it can give me a clue as to why mine shizes the bed when I push play.

I took some more readings on the PWM this morning and I am not sure of what it means. I have 300+ VDC on Pin 2, 15 VDC on the Vcc (pin 3) , and 0 VDC/AC on pin 4 (FB). Interestingly, pin 4 connects to a photo transistor on the other side of the board. It seems to me that the PWM is energized but not getting a signal to modulate the voltage across the switching transformer. I read up on switching power supplies and it seems that the PWM needs a signal from the DC run circuit to tell it to start switching the DC across the transformer. Here are the readings I took:

Really great documentation here, well done!
Couple of observations.
-if you are getting the 3.3,8ish,15 on the secondary then the bias converter PWM is working correctly.
-The reason you are seeing 0V on the transformers pins is because you are looking at AC with your meter set to DC. Those biases measured in the logic card say to me that the bias converter is running and the output is making its way to the logic card. Good sign
-I can only think of one thing left to do, and that is measure the output of the buck converter on the bottom of the logic card. There is a inductor with a (normally) yellow electrolytic cap. Solder a wire to the striped side of the cap and put the card back in and plug in. You can put the red lead on the wire and the black one to chassis. Should have 1.5V output.

Do you know much about reading serial (UART) from a computer? You may have noticed a 4 pin header under the EMI shield that you removed. There may be some diagnostic clues coming out of that serial headder.

The one I am working currently has a confirmed good power and riser boards and shows up in the Sonos app but when you push play I get orange and white blinking leds. Wanting to read that header and see if it can give me a clue as to why mine shizes the bed when I push play.


Thanks gruv2ths: I just saw your reply after I posted my recent reply about the PWM readings. Not sure about reading the UART. I have used serial ports in the past, but only to connect to consoles on enterprise class network switches.

I will have some time later to try your suggestion about measuring the 1.5 V of the buck converter and will post my findings.

Is this the cap that you are talking about?

I almost forgot. Check that you have continuity on the windings of your transformer. It’s not inconceivable to blow a transformer.