Repair ZP120

Ok.... this is revealing. This would appear that your transformer is bad. The AC through the transformer should certainly give you output voltage on the secondary...

Just to verify... you are measuring the output of the transformer... NOT the board?

gruv2ths - What do you think?

Look at this:

https://www.wikihow.com/Test-a-Transformer

The shaper looks good since you have AC on the inputs. You show 0v outputs. From this doc, it appears you may have found your problem. Your transformer looks bad.

Be warned once again RE those terribly designed stubborn clips. I saw gruvs post about Bending the pins on the MOSFETs when putting the clips back on. When I reassembled, I didn't use the little condoms Sonos included and just had the clip on the metal of the shottkey diodes (D16005). guess that was shorting the 36V line again. back to fully operational. 

My Dmm shows 0V as well. The scope says otherwise. So look past the diodes for the output of the converter. You’ll notice that from each non-RTN transformer pin there is a trace that connects the rectifier diode. Look at the cathodes of those diodes for the positive outputs.

Mine doesn’t have the True RMS feature, and that may be why?

Ando, did you get the voltages coming from the riser board to the logic board?

No I meant the voltages at the riser board connector with the logic board removed.

The idea is to make sure your non functioning logic board is getting the bias it is expecting. We can compare what you read to what my working riser card is delivering. So check all the riser card output pins to chassis.

Hey Ando,
No luck but no time to mess with them.
Check the 10 ohm resistor. It is axle leaded and 2 W and on top of the board.
If it reads 10 ohms then replace the PWM again.
That SHOULD get you back in the road.

I hope this thread is not dead.

I just got a ZP120 that can't power on. I have tracked down the main power transformer is dead: the primary windings are broken: from 1(RTN) to 2 is OL, 3(RTN) to 4 is 1.8ohm (this is the only good one), 3 to 5 is OL. Due to this problem, all secondary outputs are 0V.
I am wondering if the transformer part can be purchased anywhere. Otherwise I am open to other alternative Solutions like external power supplies?

Did you remove the transformer and check it? The only way to really know is to test it off the board. Transformers are tough to go bad...it takes a lot to blow one.

If you did test it off board, there usually is a number on the transformer. You may be able to go to Alibaba and search for the number/MFR to try to get a match. The other option is to get the size and windings (i.e. the specs) and try to get a replacement. If its the main Xformer, then that can be fairly standard as its a step down to generic voltages. You may be able to determine the windings from the front side voltages to the secondaries based on the output voltage (i.e. 120v to 3.3v == 120/3.3 ~ 36:1 winding, so on and so forth). You can also reach out to the MFRs and state the input/output voltages, and they can usually find one for you. You would need to give them the size... maybe some pics, etc.

Final option is look for a ZP120 on eBay that is dead as a door nail and try to get it for $20 for parts.

I hope this thread is not dead.

I just got a ZP120 that can't power on. I have tracked down the main power transformer is dead: the primary windings are broken: from 1(RTN) to 2 is OL, 3(RTN) to 4 is 1.8ohm (this is the only good one), 3 to 5 is OL. Due to this problem, all secondary outputs are 0V.
I am wondering if the transformer part can be purchased anywhere. Otherwise I am open to other alternative Solutions like external power supplies?

Not dead... nobody has had anything broken or came back :-)

Did you test that transformer off board? That's critical as being on board can give you different numbers depending on the circuit or if something is blown/shorted. Transformers do not blow very often and are fairly stable. Take a really good look at it off board and see if you see any evidence of charred marks or something if it registers bad. If it registers good, then its something else and you will need to do a bit more detective work.

If you are 100% sure its the transformer, you usually can find a number or code on it. You can search for that on Alibaba or reach out to some of the Chinese transformer manufacturers and see if they can find it. If not, you have the input and output voltages, so you can can give that to them as well to see if they can get a match. You can generally determine the winding ratio by dividing the input by the output... i.e. 120v to 3.3v = 120/33 ~ 36:1 winding for step down. You will need to calculate that for each input/output. You could also unwind it yourself and get an accurate winding count. Since its the main transformer, its a reasonable chance that its standard. If you can get the MFR, you can always contact them and they should have them on hand. However, there is a chance its a custom wind, and you would need to reverse engineer those windings yourself.

The last possibility is check eBay for a seriously bad ZP120 and see if you can grab it for $20 and just pull the transformer out of there.

So I gave up on trying to solve the problem with the existing circuit.  I ended up replacing the 240k resistor at R16082 with a resistor divider network.  I used 15k+4.7k+100k, with one leg of the 100k tied to the 59k resistor, and one leg of the 15k tied to GND.  The junction between the 4.7k and 100k resistor should then end at about 18V (ie approx (15+4.7)/(15+4.7+100+59)*sqrt(2)*115).  I tied that to the VCC input of the PWM.  I used ¼ watt resistors for all three of the resistors.  The lower resistance at R16082 (~120k instead of 240k) drops the voltage at the junction between R16079 and R16082 to 109V.  The current flowing through the resistor divider is 0.9 milli-amp when the PWM draws no power, and <1.1mA when it acts as a short circuit.  As a result, power dissipation for the largest resistor (100k) in the resistor network is under 1/10 watt (making the ¼ watt resistors overkill)

The circuit works fine now.  I didn’t time it, but it may take a couple of seconds longer to boot up.  There is a 100uF capacitor on the PWM VCC, and that needs to charge up before the PWM VCC line exceeds the 16V it needs to start oscillating.  Otherwise, there is no issues with the circuit.

Maybe this only works so well since the PWM chip is tolerant of voltage fluctuations on its input (it needs to start up with >16V, but then will operate with any voltage from 8-24V).  The original circuit may have provided a more stable VCC, but it’s just not needed given there is only one chip drawing less than a milliamp.