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Old 13th July 2010, 04:57 PM   #21
shawnk is offline shawnk  United States
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Zeners are ok.
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Old 13th July 2010, 05:22 PM   #22
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The D40 or D41 may be defective. You'd need to pull them and confirm that there's no short/leakage. Also confirm that the B-C and B-E junctions read ~0.6v.

Do you have a scope?
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Old 13th July 2010, 05:32 PM   #23
shawnk is offline shawnk  United States
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The board isn't labeled and unfortunately I don't have a schematic.

I'm assuming D40 and D41 are the verical diodes that are close to the bias pot?
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Old 13th July 2010, 05:33 PM   #24
shawnk is offline shawnk  United States
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I do have a scope, but my probe is a horrible generic one. :-(
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Old 13th July 2010, 05:47 PM   #25
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The D40D8 and D41D8 should have those numbers printed on them. They're transistors.

With a load connected, do you have half of the waveform missing? If not, how is the signal distorted?

Have you tried moving all pots and switches to see if the distortion changes?
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Old 13th July 2010, 05:56 PM   #26
shawnk is offline shawnk  United States
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OK.. my mistake. I see what you are referring to now.

I will pull them out shortly and test them.

The distortion is audible. I have not used the scope just yet.
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Old 13th July 2010, 10:45 PM   #27
shawnk is offline shawnk  United States
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Ok so something doesn't seem quite right with these BJT's

I've measured them out of circuit and here's the results:

D41D8

B-C: 0.70v
B-E: 1.38v
C-E: 0.00v
E-C: 0.70v

D40D8 (leads reversed)

B-C: 0.70v
B-E: 1.15v
C-E: 0.00v
E-C: 0.70v

There shouldn't be ~1.xx volts across B&E correct?
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Old 14th July 2010, 03:35 AM   #28
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It appears that they may be defective but I think you have the pin configuration wrong. Left to right it's EBC. If they don't read open from emitter to collector, that would indicate that they're leaking.
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Old 14th July 2010, 04:34 AM   #29
shawnk is offline shawnk  United States
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Ok.. I tried to find some info on these but couldn't come up with anything and after the readings I thought they might have an uncommon configuration.

In the long run E-C is in fact open

So I guess we're back to square one. Should I reinstall these?

Thanks!
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Old 14th July 2010, 12:41 PM   #30
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If you get 0.7v on one direction B-C or B-E but they read open when the probes are reversed, they're likely OK.

Did you look at the speaker output signal with the scope yet?
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