Repair ZP120

Lyricist III

@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:

Lyricist III

Are you absolutely sure that your PWM is good? What you are showing is evincing that you aren’t getting reasonable switching out of it.

Lyricist III

Are you absolutely sure that your PWM is good? What you are showing is evincing that you aren’t getting reasonable switching out of it.

I’m not entirely sure but I did replace it with a new one a while ago. I do have some more new ones that I can try. Do you know how I can test the PWM to see if it is good?

G

gruv2ths

Trending Lyricist I

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.

Lyricist III

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:

Lyricist III

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?

Lyricist III

Test that optocoupler too (no power of course). Your multimeter can test it with the diode test function. Also, if you tested that secondary transformer, and aren’t getting the matched voltages, then yeah, it’s not switching. I can test the ohms across my pins on my PWM to list them here, but you can do the same if you have extras.

Lyricist III

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

Lyricist III

Test that optocoupler too (no power of course). Your multimeter can test it with the diode test function. Also, if you tested that secondary transformer, and aren’t getting the matched voltages, then yeah, it’s not switching. I can test the ohms across my pins on my PWM to list them here, but you can do the same if you have extras.

Just checked the optocoupler and it seems fine according to the spec sheet. From the spec sheet:

Pins 1 and 2 are the IR Diode
Pins 3 and 4 are a NPN transistor

I set my meter on diode check setting:
- Pins 1 and 2 give a short beep and 0.528 reading
- Pins 3 and 4 give a short beep and 0.619 reading

That looks to be good

Also both the primary and secondary winding pins have the following continuity:

Primary:

Pins 1 to 2 = 0.08 Ohms
Pins 3 to 4 = 1.9 Ohms
Pins 3 to 5 = 2.8 Ohms

Secndary:

Pins 1 to 2 = 0.7 Ohms
Pins 3 to 4 = 0.7 Ohms
Pins 3 to 5 = 0.7 Ohms

This seems to be good as well.