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Old 2nd December 2017, 12:45 AM   #21
Perry Babin is offline Perry Babin  United States
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Do this again but do each channel twice. Check then reverse the probes and re-check.
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Old 2nd December 2017, 01:25 AM   #22
Jeff Mills is offline Jeff Mills
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Quote:
Originally Posted by Perry Babin View Post
Do this again but do each channel twice. Check then reverse the probes and re-check.
Interesting Results

Channel 1 (test 1 & 2) beeps, numbers flash eventually land on 469 ohms
Channel 1 (test 3) reversed leads beeps, numbers flash eventually end on 468 ohms

Channel 2 (test 1 & 2) 1320 ohms
Channel 2 (test 3) reversed leads OL

I also tested 3 open transistor resistors in the output section channel 1.

Last edited by Jeff Mills; 2nd December 2017 at 01:35 AM.
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Old 2nd December 2017, 05:32 AM   #23
Perry Babin is offline Perry Babin  United States
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Do any of the output transistors read as shorted or leaking?
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Old 2nd December 2017, 02:39 PM   #24
Jeff Mills is offline Jeff Mills
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Originally Posted by Perry Babin View Post
Do any of the output transistors read as shorted or leaking?
Yes sir - 3 of the 4 channel 1 output transistors tests shorted with my MM in circuit across C & E. These are the same 3 with open resistors.

I've forgotten how to test for leaks with a MM but i suspect it's a matter of reversing the leads across Base & Emitter? Is that correct?

Another stupid question where a good source to purchase a variety of 1/2 watt resistor values commonly used in car amps? I used to just drop by the local radio shack but they've closed so many of their brick and mortar stores, I don't have one near me any more.

Last edited by Jeff Mills; 2nd December 2017 at 02:47 PM.
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Old 2nd December 2017, 03:16 PM   #25
Perry Babin is offline Perry Babin  United States
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To check for leakage, you use 'ohms' and check all combinations both ways. The meter should only react in one direction.

Mouser and digikey are good sources for anything you need for repair.
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Old 2nd December 2017, 04:14 PM   #26
Jeff Mills is offline Jeff Mills
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Quote:
Originally Posted by Perry Babin View Post
To check for leakage, you use 'ohms' and check all combinations both ways. The meter should only react in one direction.

Mouser and digikey are good sources for anything you need for repair.
Perry thanks for taking time with me on this - I really do appreciate you. One last question if I may while I wait for parts to arrive.

My thoughts about how to approach this repair / rebuild is to work from the DC source in to the other side. So first is making sure the power supply circuitry is up and operational, then the rectifer circuity, next would be the output, then finally the ac input (RCA) back in to the output.

If I recall correctly... the power supply should produce a nice flat pos and neg voltage. What the voltage is I'm not sure but both voltages should be mirrors over each other (pos & neg) is that correct? These voltages feeds the rectifer. The rectifer then flips the neg to pos to establish the rail voltages that in turn feed the output section?

Like I said it's been so long (mid 80's) since I learned about this stuff and it's really kind of sad I've forgotten a lot of what I learned. That old saying if you don't use it you loose it is true for me.
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Old 2nd December 2017, 04:35 PM   #27
Perry Babin is offline Perry Babin  United States
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Point out the resistors that were burned on a photo.
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Old 3rd December 2017, 12:34 AM   #28
Jeff Mills is offline Jeff Mills
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Quote:
Originally Posted by Perry Babin View Post
Point out the resistors that were burned on a photo.
Screws are pointing to the 3 open resistors on channel 1
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Old 3rd December 2017, 12:44 AM   #29
Perry Babin is offline Perry Babin  United States
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Did you pull them to check them? They are different values.
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Old 3rd December 2017, 03:37 PM   #30
Jeff Mills is offline Jeff Mills
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Did you pull them to check them? They are different values.
Hey Perry no not yet, waiting on parts still.
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