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Old 11th March 2012, 05:45 AM   #1
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Join Date: Oct 2011
Default PPI 2050M

Greating everyone again!

Next Amp I would like to get refreshed is my old PPI 2050M. Bought this amp in the early 90's. It will still work but does have a Hum from the amp (power supply??) but both channels still work.

Only thing that has been done to the amp was the Diodes were resolder back in by a friend tech about 10 years ago.

Now I see the R17 resister on Q10 has been lifted and the caps do show they have been getting hot. C25, C32 and C33.

Correct me if I'm wrong, but I think C25 is a 1900uf 50 vdc and the other 2 are 1000uf 50vdc.

Knowing that this amp is 20 years old, is there any updates that need to be done to allow it to work better. Replacing the 3 caps and resoldering the R17 will be done..

I do also have 4 other ppi amps that are sill working fine. 3 each of the 2025am and an 2030m. If those amps need diffrent updates, will make a new post.

Thank you in advance for any help!

Anothertime
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File Type: jpg diodsppi2050.jpg (67.3 KB, 71 views)
File Type: jpg resistorppi2050.jpg (52.3 KB, 70 views)
File Type: jpg capppi2050.jpg (47.8 KB, 69 views)
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Old 11th March 2012, 11:37 AM   #2
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Join Date: Apr 2011
Location: Anchorage AK
Just from the pics, c26 looks like poo. I would look at replacing all electrolutic caps, given the state of so many. I would also have the 4 diodes pulled, tested, and re-soldered a bit cleaner. The diodes are just my anole opinion.
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Old 12th March 2012, 05:56 PM   #3
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Join Date: Nov 2003
Location: Louisiana
A hum is generally from a low frequency source like the mains. How are you powering the amp?

What's the signal source?
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Old 13th March 2012, 03:59 AM   #4
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Join Date: Oct 2011
4ga power and ground, distrubution block with fuses because PPI M series has no fuse at the amp.

Singal source is an Alpine CDA-117 with Imprint. (active crossover in the Imprint) Scosche RCA, Kimber Kable 4pr speaker cable. Amp was running Soundstream Refrence 6.1 mid's.
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Old 13th March 2012, 06:56 AM   #5
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Join Date: Dec 2005
Location: Northern California
R17 and R19 both look burnt, and for the one that is pulled up I might be inclined to say its output is also possibly damaged.
All the large caps look heat beat. Perhaps you could find some 105C rated ones to replace them with. They don't make caps like these any longer by that I mean the style of case and side ways mounting. I still have some very old stock I refused to throw away, but I test them before installing them due to there age and shelf life issues.
The diodes that have been re-soldered back in are prone to over heating under load due to the fact they are slow speed diodes to begin with. I replaced a many back in the day due to failures. I used higher speed diodes to lower the heat issues somewhat. PPI reverse mounted them under the board and sitting against the sink with heat-sink compound on them trying to resolve the issue. IMHO opinion faster diodes are in need and they also can be under board mounted against the sink just in case the heat issues are still present in some fashion.

That is about all I see in your pictures you posted, but I have seen other issues on these. Blown channel outputs and drivers MPSA06 and 56. Blown emitter resistors like you have in pictures. Many times the diodes failed and or melted the solder and just fell off the board due to low ohm loads being presented to these amps. As stated above PPI moved them under neath the board and soldered them in a assembled amp after the board was mounted so they would rest against the sink inside the amp, then they added heat sink compound and a insulator after their install height was set by soldering after the main board was mounted.

bad gain pots were common. Noisy and fall outs in their spans. Along with broken RCA's, Burnt snubber filters across the toroid secondary, Blown power supply MOSFETs or Transistors. The RP diode on the 12 volt input was also a common failure after some owners hooked them up backwards to power. Made a mess of the power supply most of the time.

Fixed a lot of these back in the day. Owned three of the 2150's myself. Hope some of this info is handy to you...
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