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Old 8th January 2019, 12:32 AM   #21
T3GTerry is offline T3GTerry
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Join Date: Jan 2019
I tried to make sure I got these correct.

Q101B = +70.4VDC
Q103B = -71.3VDC

Q102B = +70.7VDC
Q104B = -71.4VDC

R127 = -1.64VDC
R129 = 1.72VDC

R179 = -.3VDC
R181 = -.34VDC

R180 = -.13VDC
R182 = -57.1VDC
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Old 8th January 2019, 12:35 AM   #22
T3GTerry is offline T3GTerry
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And again thank you for your help. I do electronic diagnostics and repairs on a lot of automated machinery but never did much audio. So some of this is beyond my paygrade.
But thank you again.
I feel like a bull in a china shop with just enough smarts and strength to be dangerous.
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Old 8th January 2019, 01:48 AM   #23
T3GTerry is offline T3GTerry
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Ok it looks like I got the transistor reading wrong. My bad. A very long hard three days. I am rattled. Let me get those transistor readings again.
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Old 8th January 2019, 01:58 AM   #24
T3GTerry is offline T3GTerry
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Q101B = -2.27vdc
Q103B = -2.27vdc

Q102B = +2.28vdc
Q104B = +2.30vdc

Sorry about that.
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Old 8th January 2019, 04:51 PM   #25
llwhtt is offline llwhtt  United States
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Location: SoCal
Are you sure about R182? It should be the same as R180 or close to it. The left channel shows more current thru R179/181 but that's normal as the left channel is also the supply for the Zeners and opamp.

So you have the same voltage on the bases of Q101/103 but different voltages on the collectors along with very minor difference on the emitter, why? If R123 and R127 check out Q101 might be the cause. It all starts going downhill at Q101 and after.

Have you ever checked the DC offset on the output of the amplifier?

Craig
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Old 8th January 2019, 08:33 PM   #26
T3GTerry is offline T3GTerry
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Checking again
R180 = -.13vdc
R182 = +56.0vdc
(Not questioning your expertise because I am the student here but, on my amp circuit board and on my schematic, 180 and 182 are not even on the same end of the board. And not the same size resistors. The only compliment to R182 that I can find is R183. It measures +57.3vdc. Are you thinking R178? R178 = +.14vdc.) Or am I confusing this?

Vb Q101 = +2.2vdc
Vb Q103 = -2.2vdc

Vc Q101 = +70.4vdc
Vc Q103 = -71.1vdc

R123 = 1.10vdc
R127 = 1.66vdc

DC offset = 1.1mv
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Old 8th January 2019, 09:00 PM   #27
llwhtt is offline llwhtt  United States
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R178-181 are all 22 Ohm, red red black, resistors. These are what supply the front end with voltage. I think I asked for the wrong ones, I started with R179 and went up from there, should have started with R178. oops!

Craig
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Old 8th January 2019, 09:36 PM   #28
T3GTerry is offline T3GTerry
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Hahaha no problem. I'm old but never too old to use the brain.
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Old 10th January 2019, 02:25 PM   #29
T3GTerry is offline T3GTerry
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I am guessing that at 1.13vdc R123 does not check out? I am basing that on what you said about the three using .6vdc each. Can I surmise that R123 should have been more like 1.7vdc? Would this also support your suggestion that possibly Q101 is a problem?

Or did I just confuse the whole thing?

Ok I have tried to pay close attention to everything you are helping me with and I have tried not to interject things I have seen and observed because I did not want to mess up your train of thought. So not I am going to ask a question based on something I observed and maybe this will help and maybe it won't but hey I will never know if I don't ask so here goes; While comparing voltages from left channel to right I observed that the collector voltages of Q105 wasn't even close to it's right channel equal. Q107 was spot on. Could this be a problem OR was it just more evidence of what you suspect is the problem?

Thanks again ........ I am eventually going to ask for your address so I will know where to send your birthday present.
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Old 10th January 2019, 05:19 PM   #30
llwhtt is offline llwhtt  United States
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Back on post #16 you confirmed that the voltage drops across R123 and R131 were low compared to the negative half. This means that both Q101 and Q105 are not conducting enough current. Q105 is supposed to do what Q101 tells it to do. Since the voltage drop across R123 is too low then Q101's collector voltage must be too high to make Q105 conduct properly and causing Q105's collector voltage to be low. Q101 is biased by the opamp's Zenered supply. What's the voltage drop across R119 and R121? Also when you find a difference across resistors make sure the resistors are the correct Ohms.

Craig
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