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Old 10th March 2005, 12:34 AM   #11
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I just bought a non-working PCR800. After inspection I can see that some of the drive transistors are falling off the PCB. They are 2N3440 and MM4003. I can't find the MM4003's. Is there a replacement? Should I upgrade both types with something newer?

Any suggestions greatly appreciated.

Blessings, Terry
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Old 10th March 2005, 02:11 AM   #12
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Good luck finding MM4003's! i have found a grand total of 3 in the whole US still left anywhere! and they want 16.00++ each! been looking for years!

Here is the funny thing...the 2N5416 is the actual device match to a 2N3440, but SC choose to use the 4003 which has half the current rating of the 5416...why? best i can figure is they were trying to speed macth the differences in gate cap charge time. but that is just a guess on my part. maybe they choose that device because it is more linear...who knows....


when i repair these, i just use 5416's and i have never heard any real differences. However. i sure would like to find a NOS stash of MM4003's just to do some testing with...

Oh yeah, only use Motorola devices, the others are NOT the same! they sound different.


Zc
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Old 10th March 2005, 05:34 PM   #13
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Hi Zc,

In another thread you mentioned having the schematic for the PCR800. Would you still be willing to email it? If so, i would really like to have that. The main board in this amp I just bought looks as though it was under water or something at some point. manyt of the leads to the resistors are corroded. I should probably replace them as well. I would rather replace them with the correct values rather than trying to measure them.


Thanks so much, Terry

still4given@yahoo.com
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Old 11th March 2005, 01:47 PM   #14
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A friend had mailed copies of the schematic a while back. I had forgotten I had them. Now to figure out how it relates to the PCB. Not as easy as I had thought it would be.

I've got a couple of questions if I may impose on some of you. Quite a few of the components have that greenish corrosion on their leads. Is there some type of cleaner that will remove that? I tried scraping them but ended up breaking one of the leads to a diode. Now I have to figure out what it is so I can replace it.

What's weird is that only some of the components have the corrosion on them. Others that are right next to them are fine. Could this be some sort of electrolysis? The little TO-39's are all just falling off the board. It's like something just ate away the leads on them. Very strange. Except for a few diodes the rest of the components seem to be fine.

Is there a trick to tracing out the schematic on the PCB? Anything to look for that would make it easier?

Thanks, Terry
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Old 16th April 2014, 03:45 PM   #15
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Default RE; Soundcraftsmen shoebox amps

Hey guys,

I was brought a partially-disassembled PM840 for service. The main problem is, that someone disconnected all of the wires on the front of the power amp board, going to the power supply board. Anybody have photos from the top down, showing which colors go where?, or even a list from left to right as to which color wires go to which pins, on the amp board. I think I have it figured out, but want to be sure. Also, anyone have a good source for the S.C.R's in the power supply, as two of them seem to be blown. Thanks everyone!
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