Repair ZP120

Lyricist III

@ando1 - Great photo... looking at your picture, it appears to have liquid damage... looks like it got wet. Pretty good chance replacing the parts and perhaps finding if there is another short may fix it.. Its just a hunch. As stated before... when you do get a chance to replace the components, dim bulb it and see if the light blinks. If not, probe for a warm/hot part nearby...

Also... If those are the 1000uf big caps, that are in that picture... they normally have plastic caps on them to prevent the board from causing a short. I would recommend putting the plastic caps back on them or place some electrical tape over them to shield them from touching the board.

Lyricist III

@m0untainman - Yeah I was wondering what that discoloration might be on the board. Makes sense it might have water damage seeing that the top of the amp is full of holes 😳 I ordered some of the caps and resistors form eBay. As soon as they come in I will replace and see what happens. Thanks for all the help so far and I hope you have a great holiday!

Lyricist III

@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?

Lyricist III

Yep... you are good. 🙂

Lyricist III

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!

Lyricist III

Well all the parts that I ordered came in and I installed them, however I am sorry to report that the amp still did not power up. I am disappointed and perplexed at what else could be causing this. Right now, the situation does not look good.

One thing that keeps bugging me though is early on when I was measuring the voltages around the bias converter. I did not have some of the same voltages that gruv2ths said he did. I am wondering if they may still be something wrong there.

@gruv2ths and @m0untainman - Could either one of you give me some detailed readings of what you have on your functioning amps as compared to the below?

Lyricist III

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).

Lyricist III

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.

Lyricist III

@gruv2ths and m0utainman - So to ask my question a different way, can you tell me what ground points you were using when you took the voltage measurements that are shown below?