Repair ZP120

Trending Lyricist I

The 15V is provided by the bias converter. All the stuff in the red square above is the 36V supply.

Lyricist III

The 15V is provided by the bias converter. All the stuff in the red square above is the 36V supply.

Thanks,
Any way you can give me some continuity readings from a good amp?

Trending Lyricist I

I cannot tonight, but I can tomorrow night.
Where would you like the readings from?

What are you measuring at the rectifier vias with the rectifiers removed?

Lyricist III

Thanks gruv2ths. If you would measure the following on the rectifiers:

pin 1 to pin 2
Pin 1 to 3

Also if you could check the 6 pins of the transformer that is closest to the rectifiers. When I checked them last night, they were all shorted together.

Trending Lyricist I

The transformer is just a bunch of coils of wire wrapped around a ferrite core, so yes with your DMM it will just look like it is all shorted together. That is normal.
As for the rectifier, i believe the outside pins are shorted together on the board and both outside pins should be high resistance to the center pin. Open the datasheet for that diode then google 'how to test a diode'. The package in question is just 2 diodes in one package. This is stuff that is good to know.
A short on the output of the 35V supply may explain why you have 0V on the Pfet. Maybe take your meter in ohms mode and measure (with the power off) the resistance from the pin of the Pfet that measures 0V to ground. I bet you will measure the same short you are measuring at the rectifiers.

Lyricist III

The transformer is just a bunch of coils of wire wrapped around a ferrite core, so yes with your DMM it will just look like it is all shorted together. That is normal.
As for the rectifier, i believe the outside pins are shorted together on the board and both outside pins should be high resistance to the center pin. Open the datasheet for that diode then google 'how to test a diode'. The package in question is just 2 diodes in one package. This is stuff that is good to know.
A short on the output of the 35V supply may explain why you have 0V on the Pfet. Maybe take your meter in ohms mode and measure (with the power off) the resistance from the pin of the Pfet that measures 0V to ground. I bet you will measure the same short you are measuring at the rectifiers.

Yea I know the transformer should show a short on some pins put it was showing across all even though the solder traces looked like they were on separate circuits. As for the rectifiers I do have the data sheet and did test one that I removed and it tested good. I am planning on removing the other one tonight and test it as well.

Please let me know what you get for your readings. I am especially interested in the rectifier pins.

Lyricist III

I removed both rectifiers tonight and checked them while referencing the data sheet. Both seem to check out OK but I am hoping gruv2ths or m0untainman can double check my work and verify. Below are the readings I got from the rectifiers while removed from the board. My meter was in the diode check mode:

After checking the rectifiers I checked continuity on the board mounting holes where they were mounted and they were all points were still shorted. I then tried removing the 2 wires that were soldered near the rectifiers. These wires are coming from the bigger of the 2 transformers. After removing them the middle mounting hole is no longer shorted to the other 2 on both rectifier mounting locations. Sorry if I am not explaining this well so I am also including some pictures and tables with my findings below.

The end result seems to be that when the 2 wires from the Xformer are connected to the board all of the recifer pins are shorted together. When they are removed, only Pins 1 and 2 are shorted.

gruv2ths / m0untainman - Please let me know your thoughts on this.

Thanks,
Andy

Trending Lyricist I

Lots of great stuff here.
Looks like the shiort is not the rectifier.
Like I mentioned earlier, there could be a lot of thing to cause a short at that point. Anything on the 36V bus.

Start taking off the electrolytic caps by one. Start with the 2 Big brown radial ones right next to the rectifiers.
Hope it’s not the Amps.

Lyricist III

My soldering iron dies yesterday so I have to wait for a replacement to arrive before I can remove those caps. I also ordered a multimeter that has an ESR function to test the caps so I will know for sure if one of them is bad. Should have everything by the weekend and can update then.