but the signal manages to reach the base of Q17-Q18, as you can see in post #21, if I measure the voltage drop across R43 and R44 I get a voltage, as well as across the resistors R45 and R46;
This is what I measured at the bases of Q13, Q15, Q17 and at the emitter of Q17, similarly for Q14, Q16 and Q18
Q14 Vb
Q16 Vb
Q18 Vb
Q18 Ve
Q13 Vb
Q15 Vb
Q17 Vb
Q17 Ve
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These waveforms all look good to me, and are reasonably consistent with the data you posted in #13. I assume if you scoped emitters of Q19 and Q20, you'd find similar waveforms.
I see you've confirmed reasonable resistance, on both Q17 and Q18? Have you traced the sine wave from the main output toward the speaker binding posts? Where does the signal fail on the path toward the dummy load? Does output change amplitude if you remove the load and test open circuit? The resistance seems reasonable, but be suspicious of the transformer. Let us know what you observe.
I see you've confirmed reasonable resistance, on both Q17 and Q18? Have you traced the sine wave from the main output toward the speaker binding posts? Where does the signal fail on the path toward the dummy load? Does output change amplitude if you remove the load and test open circuit? The resistance seems reasonable, but be suspicious of the transformer. Let us know what you observe.
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My approach to repairing a defunct Sansui amp 2years ago was to print out the parts list for the power amplifier section and to measure resistor values and use a green highlighter pen to mark the various parts which were good and and a red one to mark those that were defunct. In this way you have an image which is portable. There were some defunct carbon film resistors as I remember which I replaced. You also have the voltage points to check against your actual measurements which you could highlight in green if good and red if otherwise - in that case you could write any incorrect voltage on the print out master image.
I’m losing sight of the original problem. I’m probably being dense, but would you guide me along the path to the problem you’re encountering?
Thanks.
Thanks.
To recap......
the problem I found is the low output power (about 25W); I think that only the distortion correctors are working because, what I measure at the output terminals, is precisely the power of those transistors;
as you have seen and said, the signal has its shape without distortions or strange shapes, the voltages are consistent with those from SM;
I think we are missing something terribly banal.....
TRAFO:
in post #24 you mentioned a possible malfunction of the transformer; I think that if the output voltages match I shouldn't worry too much, among other things I also used the two primary windings of 220Vac and 240Vac, so the primaries should be ok; I will also try to use 100Vac and 120Vac, you never know....
if the transformer were to break I really don't know where to get one.
I really appreciate what you are doing and the advice you are giving me, I hope to solve it
the problem I found is the low output power (about 25W); I think that only the distortion correctors are working because, what I measure at the output terminals, is precisely the power of those transistors;
as you have seen and said, the signal has its shape without distortions or strange shapes, the voltages are consistent with those from SM;
I think we are missing something terribly banal.....
TRAFO:
in post #24 you mentioned a possible malfunction of the transformer; I think that if the output voltages match I shouldn't worry too much, among other things I also used the two primary windings of 220Vac and 240Vac, so the primaries should be ok; I will also try to use 100Vac and 120Vac, you never know....
if the transformer were to break I really don't know where to get one.
I really appreciate what you are doing and the advice you are giving me, I hope to solve it