PPI 2150 AM Dead! Need help or good repair person! - Page 4 - diyAudio
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Old 13th November 2007, 05:37 PM   #31
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UPDATE:

Well, I'm VERY happy to report that changing out the resistors seems to have done the trick! YAY!! My amp now sounds much more like it used to and will only heat up to about 128 degrees F if I really push it (I now keep my little laser temp gun in the car for routine heat checks). I got some thick-wall aluminum tubing and cut 4 little 1/2" spacers to mount under the amp so that it sits up off the carpet of my box. Figured it might help to have airflow under the amp. Time will tell, I guess...

HUGE thanks to Perry for his help getting my amp going reliably again! I don't know why it kept grenading itself with the factory resistors in it, but the change-out appears to be just what it needed. I'm keeping my fingers crossed and taking it a bit easy on the low-end tune'age for a while just to make sure the new thermal grease (arctic silver...although it's not white anymore, but a dark gray color out of the tube) gets settled in correctly. I did make sure the bottom cover was applying adequate pressure on the transistors before buttoning the amp up completely, and was thankfully able to use the original allen-head screws.

Ain't the internet a wonderful thing sometimes??

Pyro
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Old 13th November 2007, 06:02 PM   #32
ppia600 is offline ppia600  United States
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Congratulations, that is great
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Old 13th November 2007, 07:17 PM   #33
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PyroZona:
The FETs were failing because the original resistors couldn't get the FETs turned off quickly enough. This meant that both banks of FETs were on. They were essentially fighting each other. One bank is supposed to be completely off before the other bank turns on.
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Old 13th November 2007, 07:42 PM   #34
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I see, thanks for explaining that. So the replacement FETs were different than the ones that originally came in the amp? If so, I'm guessing that the original ones aren't made anymore, or something like that? If that is not the case, are they hard to get perhaps? Would there be any advantage to locating some of the original spec ones and putting those in with the original resistors? I mean, the amp sounds close to how I remember it sounding, but it still seems like it the power output starts out fine at the beginning of a song, and then drops a bit. Could be just my ears though, I suppose...or something else in the system that might cause that to happen.

I'm kicking myself for apparently accidentally tossing out (or at least having so far misplaced) the ones that were replaced that I was given when I picked up the amp the first time. I mean, if the replacements were of the same specs as the originals, I don't understand why the resistors required changing to a different value.

Sorry for the boatload of additional questions, I'm just trying to understand my amp. I do appreciate you taking the time and patience to explain all this stuff to me...as I know you have for others. You're a gentleman and a scholar.

Pyro
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Old 13th November 2007, 08:08 PM   #35
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I'm not sure what the original FETs were. I've seen several amps with IRFZ34s and the 470 ohm resistors. They worked well together.

If the Z34s are the original parts, they are still available. The Z44s are rated for more current and should make the amp a bit more reliable.
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Old 13th November 2007, 08:54 PM   #36
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More reliable? Sweet. That's what I was hoping to hear. As long as the 44's don't affect sound quality, I'll be keeping them in there.

Thanks once again,

Pyro
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Old 19th November 2007, 07:03 PM   #37
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Quote:
Originally posted by Perry Babin
I'm not sure what the original FETs were. I've seen several amps with IRFZ34s and the 470 ohm resistors. They worked well together.

If the Z34s are the original parts, they are still available. The Z44s are rated for more current and should make the amp a bit more reliable.
The originals are a weirdo number I can't seem to find information on. Of course, the part numbers I have are second hand and are probably typos: P4262. I thought it would be a P40N06 (logic level) or some other nonsense. Given that the drive circuit includes a saturable core and those "high value" resistors, I wouldn't put anything past them. It would also explain why the new Z44's were cross conducting.

It's a shame that the recommended "repair dude" did such a hack job on your amp. Drywall screws?!
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Old 19th November 2007, 07:06 PM   #38
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Originally posted by EnvisionAudio


It's a shame that the recommended "repair dude" did such a hack job on your amp. Drywall screws?!
Yeah, tell me about it. But thanks to the helpful people here on this forum, my amp is still running strong.

Pyro
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Old 20th November 2007, 04:49 AM   #39
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Strange I just worked on a PPI I have had for a long time, it is 2x75. I never used it that much but last year ran a 12 with it hard as it would go, it didn't even get warm. Then it started to back off at times, get quiet. I found one RCA was not working right. It has holes most RCA will not fit in now, the ones I have fit tight. Anyway I took it out and now was checking it. Turns out the RCA seem ok but the center part was loose on the pin so I fiddled with it, seems fine. I look around....there is a mosfet just laying there! I look and two more have at least one leg loose!

I don't know if someone replaced them or what, but they were bent and not soldered flat to the board. So I resolder all 8 of them and the power ones on the other side just to be sure. The fets were all Motorola. Before I took it apart it hardly got louder bridged than one channel, but now it does. I don't know if it was bad solder, bad job, or what. It never got hot I checked it and this old alpine I ran on highs was always hot, in fact I had a pc fan on the amps because of the alpine. I might have to try this in the car again to see what it does. I actually had to go digging in my car tools to find english allen wrenches to work on it.

Maybe it was screwed up when I got it, everyone says they are great amps but I was never that impressed with it. Also need to put terminals on it as I don't have the plug and it is a pain to plug wires into it.
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Old 20th November 2007, 01:23 PM   #40
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Quote:
Originally posted by jol50
Strange I just worked on a PPI I have had for a long time, it is 2x75. I never used it that much but last year ran a 12 with it hard as it would go, it didn't even get warm.

Before I took it apart it hardly got louder bridged than one channel, but now it does.

Maybe it was screwed up when I got it, everyone says they are great amps but I was never that impressed with it. Also need to put terminals on it as I don't have the plug and it is a pain to plug wires into it.
Ya think? PPI amps will get hot at full tilt (and be warm at idle) - that is why they put such large heatsinks on them. Your statements tell me that the amp was never operating properly. It may still not be, depending on your confidence level in the repair. Did you just resolder the parts or actually repair the amp?
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