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Sansui Eight help - hum on one channel

Thanks about the schematic, I downloaded that one from hifi engine but I am working from an iPad Pro and for some reason it does not like that pdf file
 
R836 is reading 15 ohm on one driver board and 16 ohm on the other.

bob777 said:
The main filter capacitors are 50 volt caps according to the schematic. That seems a little close for me. What is your line voltage selector set at? It might just be because we are not pulling any current. The b8 and b9 are probably ok. What is your output voltage at the driver board. Don’t leave it on longer than required to measure the voltages. That is right at the voltage rating for this big caps.
Click to expand...

Line voltage set to 117V

Driver board output voltage measured at side of R837 connected to pin H is about 40V on both boards.
 
TR804 Left: (?) -48V, (-1.32) +41.5, (?) -48

Value from schematic in parenthesis. Will have to get resistor values later as that requires lifting one leg, correct?
 
I saw you looked at voltages on tr804 earlier. Did you check that transistor? That transistor looks like it is biased on but not pulling the collector down or conducting.
 
Measure resistors in circuit, value is small enough to get a decent reading. I would check that transistor.
 
Check tr806 in circuit collector to emitter resistance just to make sure it’s not shorted power off of course
 
It seems to me that tr808 is not turned on or conducting. It is controlled by tr804 which is also not turned on or conducting. This leads back to tr801 and tr802.
 
TR001 and TR002 have both been replaced with KSA992 upon recommendation from Jim at QRXRestore in another thread.

Here are voltage readings done this morning. ECB, all readings Volts.

TR804: -49.8, 42.9, -49.9
TR801: 0.107, -50.2, -0.06
TR802: 0.14, -50.2, 9.2

TR804 E was drifting up and did not wait for it to stabilize.
 
Interesting, I can't remember if we/you checked R815, 100Ω, R814, 100Ω, and R813, 470Ω - perhaps you could try that?

But I don't want to interrupt or interfere with the help bob777 is giving you... ;)
 
Hyperion said:
Interesting, I can't remember if we/you checked R815, 100Ω, R814, 100Ω, and R813, 470Ω - perhaps you could try that?

But I don't want to interrupt or interfere with the help bob777 is giving you... ;)
Click to expand...
If you look back at post #11, R813 and 815 originally were both toasted on the L channel board, so those got replaced. However, just checked the ones you mentioned on both boards in circuit and all are ok.
 
Hey John, feel free to get back in the game. This is an odd problem. I can’t help feeling since both channels have same problem, might be something done to both driver boards. Have you checked both tr801 and 802 are installed correctly?
Is the 8 volt zener diode by vr802 ok?
 
bob777 said:
Hey John, feel free to get back in the game. This is an odd problem. I can’t help feeling since both channels have same problem, might be something done to both driver boards. Have you checked both tr801 and 802 are installed correctly?
Is the 8 volt zener diode by vr802 ok?
Click to expand...
Yes, they are installed correctly. Changing them did not change the high DC offset at all.

I did check all the diodes this morning. The zener reads higher than the other diodes. If I recall (not at home right now), one direction was 2.7V and the other was around 0.7V? I can check again when back home today if you need exact numbers.
 
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