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M500T Carver help?
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Old 4th January 2019, 04:37 PM   #11
llwhtt is offline llwhtt  United States
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If you notice the circuit is symmetric, what's on the collector of Q109 should also be on the emitter but opposite polarity. Q109 is controlling six PN junctions, three on the positive half, Q111, Q115, and Q119/121 and three on the negative half, Q113, Q117, and Q123/125. I counted the outputs as one PN junction as they are in parallel. Each PN junction voltage drop is approx. .6VDC, the turn on voltage, and since there are three of them in series the total is approx. 1.8VDC, so that's where the 1.7VDC comes from. The conduction of Q109 is controlled by SVR101 and surrounding components. The harder Q109 conducts, the less voltage drop across collector and emitter, the colder the bias which is what you are experiencing. You only have 2.8VDC should be more like 3.4VDC. If your problem is actually in the bias circuit your voltages should still be symmetric in regards to the collector and emitter but they are not. Try measuring the collectors of Q101 and Q103. Notice there is a mistake on the schematic, the collector of Q101 should be same as the collector of Q103, 73VDC NOT 7.4VDC. Remember to look for symmetry between the + and - halves of the circuit.

Craig
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Old 4th January 2019, 06:01 PM   #12
T3GTerry is offline T3GTerry
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While not exactly 74vdc they are close at 72vdc at the collectors of Q101 and Q103.
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Old 4th January 2019, 06:08 PM   #13
llwhtt is offline llwhtt  United States
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OK, try measuring the voltage drop across R123 and R125. And R131 and R133. We're looking for significant differences between the + and - halves of the circuit.

Craig
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Old 5th January 2019, 12:03 AM   #14
T3GTerry is offline T3GTerry
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I will have to do more tomorrow. I work nights, 12 hour shifts. Sleep days. So I will be off and on for a few days. Will try to get more done tomorrow.
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Old 5th January 2019, 04:14 PM   #15
llwhtt is offline llwhtt  United States
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Excuses excuses
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Old 5th January 2019, 08:28 PM   #16
T3GTerry is offline T3GTerry
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I sent a reply a little after 7 AM this morning but apparently because I am new here the mods have to approve of all of my posts as well as responses first.
R123 = .04vdc
R125 = .06vdc
R131 = .04vdc
R133 = .06vdc

Maybe this will get there quicker. Maybe both replies will.
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Old 5th January 2019, 09:17 PM   #17
llwhtt is offline llwhtt  United States
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1/3 less current on the + half, there's the problem but we need to find out why. Your 1.1VDC on collector Q109 is short approx. 1/3 of what you're supposed to have also. What's on pin 1 and 7 of the IC101? Both should be close to 0VDC.

Craig
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Old 5th January 2019, 11:08 PM   #18
T3GTerry is offline T3GTerry
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Both pins 1 and 7 are showing less than 25 mv.
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Old 7th January 2019, 03:58 PM   #19
T3GTerry is offline T3GTerry
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UPDATE .......... I have found absolutely nothing so far. I am lost. And feeling pretty stupid so far.
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Old 7th January 2019, 05:04 PM   #20
llwhtt is offline llwhtt  United States
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Voltage on bases of Q101/103 and Q102/104? Voltage drop across R127/129? Voltage drop across R179/181 and R180/182?

Craig
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