ZPA0.3 Basket Case Repair
Posted: Sat Jul 11, 2020 12:34 pm
This is a ZPA0.3 I got in from a client a little bit ago. This was quite literally a "basket case". This is how every tech likes to receive their work... Wrapped up in pieces in a box.
Anyhow, the client has owned the since new (more in this later, it's an odd part of the thread). It was supposedly sent in to PG twice for repair. Once for a repair and once to have the v2 mods done.
The client said he had a lot of soldering and electronics experience and asked me for help to initially recap the amp. I gave him a lot of tech support and he got the recap done but the amp had other issues and while trying to troubleshoot he misread my warning not to turn the bias pots while the amp was out of the sink and he turned one and blew the entire channel in a heartbeat.
So, the amp shows up in a box in pieces. One of the new caps was cocked off the board. The solder joints were very cold and I could tell from the feel that at least some had pulled plating. So on top of the rest of the repair I had to redo the recap and fix the ripped out plating.
I start investigating and I find that both power supplies are blown. Not only do they have two different mismatched batches of irfz44s in them, there is also one 55n06 in the mix. The 55n06 is very nearly the same mosfets, but not close enough that if trust them to share the load equally.
I notice that some of the schottky rectifiers in the rail switching circuit are looking a little discolored, like they've gotten hot. So I take a look and find two different rectifiers in the 4 positions, and none of them are schottky rectifiers, they are all standard rectifiers.
I also found that the two vertical cards were missing several pads on the bottom of the board. Yup, a bunch of ripped out plating there too.
I rebuilt the supplies, fixed all the board damage and installed the proper rectifiers. I bring it up because supposedly PG did this work. I told the client that I was basically dumbstruck. I've never seen anything come out of PG that was that bad. He said one time he sent the amp in himself, and the other time the stereo shop sent it in. I'm of the opinion that shop never actually sent it to PG, but rather did it in house or used a local "expert". We may never know, but I hope to God PG didn't do it.
In the end, one channel and the drivers had to be replaced as well. The amp ran flawlessly after all that.
Anyhow, the client has owned the since new (more in this later, it's an odd part of the thread). It was supposedly sent in to PG twice for repair. Once for a repair and once to have the v2 mods done.
The client said he had a lot of soldering and electronics experience and asked me for help to initially recap the amp. I gave him a lot of tech support and he got the recap done but the amp had other issues and while trying to troubleshoot he misread my warning not to turn the bias pots while the amp was out of the sink and he turned one and blew the entire channel in a heartbeat.
So, the amp shows up in a box in pieces. One of the new caps was cocked off the board. The solder joints were very cold and I could tell from the feel that at least some had pulled plating. So on top of the rest of the repair I had to redo the recap and fix the ripped out plating.
I start investigating and I find that both power supplies are blown. Not only do they have two different mismatched batches of irfz44s in them, there is also one 55n06 in the mix. The 55n06 is very nearly the same mosfets, but not close enough that if trust them to share the load equally.
I notice that some of the schottky rectifiers in the rail switching circuit are looking a little discolored, like they've gotten hot. So I take a look and find two different rectifiers in the 4 positions, and none of them are schottky rectifiers, they are all standard rectifiers.
I also found that the two vertical cards were missing several pads on the bottom of the board. Yup, a bunch of ripped out plating there too.
I rebuilt the supplies, fixed all the board damage and installed the proper rectifiers. I bring it up because supposedly PG did this work. I told the client that I was basically dumbstruck. I've never seen anything come out of PG that was that bad. He said one time he sent the amp in himself, and the other time the stereo shop sent it in. I'm of the opinion that shop never actually sent it to PG, but rather did it in house or used a local "expert". We may never know, but I hope to God PG didn't do it.
In the end, one channel and the drivers had to be replaced as well. The amp ran flawlessly after all that.