Repair ZP120

Also the 36V supply only comes on when you push play from your phone. Before that it is OR’ed with the 15V from the bias supply.

Yeah I know I do get hung up on those secondary voltages ? I will say one last thing though about them however. I did check on both AC and DC and both are 0V.
The RTN points on the secondary are shorted at 0 OHMS and I did have the ribbon cable plugged in when I powered the amp on.
I also plugged in a network cable to the port and there is NO activity.

Also just for giggles, I replaced the PWM again to see if that would help but it made no difference.

I need to make a ribbon cable so that I can plug in the logic board while it is laying on the bench remotely via the cable. That way we can define the pins that connect to the logic board then see what's missing when one doesn't work.

I have a bad logic board now that as soon as you push play it throws an error and you get no sound. And I have no idea what the problem is.

Just checking in... ando1 - Congrats on finding the short 😉 The IC 😉 You made HUGE progress which is excellent. Looks like you are moving in the right direction! Don't give up!

I put the amp back together and tried powering on (with the dim bulb tester inline) and no joy. No white light on the front panel.

Did you put in a new STA508 when you put it all together? Or were you just testing the power supply? Also you can get it from Mouser... its a STA50813TR

https://www.mouser.com/ProductDetail/STMicroelectronics/STA50813TR?qs=sGAEpiMZZMtxdzBvM0rKcUDV0cGqXNcOK%252bjnReF%252bddw%3d

I just put the amp partially back together without the STA508. According to gruv2ths the amp should boot normally (white flashing light). Thanks for the mouser link but I found a US based eBay seller and ordered 2 at $10 each. They should be here next week.

ando1... while you are waiting, I am interested in something. Please confirm you have voltages on the PRIMARY side the PWM transformer (it should be AC). If you do, could you please lift the transformer from the secondary side and test that you have voltages on the secondary transformer pins while they are not connected? I am interested to see if something on the secondary side of the circuit is pulling down your voltage (short?) or if perhaps that transformer is indeed bad. If the transformer is good, you should see voltages on the output pins of that transformer. If you get AC voltages on the primary (output from the PWM) but nothing on the secondary, then your transformer is likely toast. If you suddenly have voltages on the lifted secondary pins, then your transformer is good and your problem is down stream. You can also test for a short while that side of the transformer is up off the circuit.

Your voltages on the primary look good. Unsolder the secondary and try to gently bend it up. Stick a business card or something that has no conductivity underneath it to keep it from touching the contacts below. If that's too difficult, you could remove it and just wire some jumpers with alligator clips to the primary.

Be careful not to short anything because that PWM will go kapow. Take it slow and methodical.