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How can this be? Sansui G9700 moving from SS

jefferylhenr

jefferylhenr

AK Subscriber
Subscriber
I have a normally functioning G9700 and trying to set the bias. The manual says 5mv, but I am getting 246mv both left and right with the vr all the way counterclockwise. Everything acts normal, the mv climbs and stabilizes, the voltage responds directly to the vr. I have tested the fuse resistors and they are showing 1.43 k ohms in circuit - I believe the manual says 3.3 k ohms.

Before I start pulling parts, etc. wanted to check here for thoughts. The unit doesn’t heat up or draw excessive current. This is what I am working with
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The bias adjustment quite possibly works the opposite of what you're doing. This is the case on the G8000/9000.
The driver circuit is very similar, so what I would do is turn the trimmer clockwise slowly and see if this makes the bias setting decrease, if it does then continue until you get to 5mV....
Don't run the unit for too long with the large idle current it has now it might start oscillating and then blow the output transistors and so forth...
 
jefferylhenr said:
There does appear to be a conflict between the schematic and the instructions.
Click to expand...
Measuring the bias voltage between the emitters of TR02 and TR03 (as per the service manual instructions) is electrically equivalent to the measurement between the emitters of TR03 and TR04 (as shown in the schematic).
 
kevzep said:
...Don't run the unit for too long with the large idle current it has now it might start oscillating and then blow the output transistors and so forth...
Click to expand...
+1
The initial bias adjustment can be made whilst the unit is on DBT (with a 100W bulb), this will afford some protection from damage.
 
But if using the DBT, turn it back down close to ZERO (0) or when you put it on wall it'll be higher. Readjust on wall voltage to spec. Over on PIONEER we call it "Tickling the Dragon!"
 
So the schematic indicates 5mv across the emitters of ie R03 and R04. Turn the vr full counterclockwise and then I can only assume start turning clockwise until you reach 5mv after allowing everything to stabilize after 10 minutes. Typically this is done with no input, zero volume and speakers off.

I do use a dbt for initial startup but then switch to an inline current meter on the AC plug main to monitor what’s going on while a unit heats up and stabilizes. This one sets dc offset fine and the mainline current draw is stable at about 350ma. It plays fine and drives speakers fine with a stable main line current draw and no concerning heating.

When I measure across the emitters per the manual, I get at most 0.06mv after 10 minutes and no response to the vr. When I measure across the base I get 240 mv and full response to the vr. Exactly the same on both left and right channels. I can’t imagine both sides have the same issues? I see no indication of prior repairs or modifications. And using two different meters. Yes I know it sounds like I am a noob like I am doing something stupid, but that is not the case.

I just rebuilt and set up an 8700 a few weeks ago with no anomalies and probably 30 different Marantz, McIntosh, Luxman’s, Sansui, Kenwood, Pioneer in the last year and most DOA. This 9700 is a head scratcher.

Well tomorrow is a new day.
 
jefferylhenr said:
So the schematic indicates 5mv across the emitters of ie R03 and R04. Turn the vr full counterclockwise and then I can only assume start turning clockwise until you reach 5mv after allowing everything to stabilize after 10 minutes. Typically this is done with no input, zero volume and speakers off.

I do use a dbt for initial startup but then switch to an inline current meter on the AC plug main to monitor what’s going on while a unit heats up and stabilizes. This one sets dc offset fine and the mainline current draw is stable at about 350ma. It plays fine and drives speakers fine with a stable main line current draw and no concerning heating.

When I measure across the emitters per the manual, I get at most 0.06mv after 10 minutes and no response to the vr. When I measure across the base I get 240 mv and full response to the vr. Exactly the same on both left and right channels. I can’t imagine both sides have the same issues? I see no indication of prior repairs or modifications. And using two different meters. Yes I know it sounds like I am a noob like I am doing something stupid, but that is not the case.

I just rebuilt and set up an 8700 a few weeks ago with no anomalies and probably 30 different Marantz, McIntosh, Luxman’s, Sansui, Kenwood, Pioneer in the last year and most DOA. This 9700 is a head scratcher.

Well tomorrow is a new day.
Click to expand...
Oh, I forgot, Sanyo, Denon an Yamaha
 
jefferylhenr said:
When I measure across the emitters per the manual, I get at most 0.06mv after 10 minutes and no response to the vr. When I measure across the base I get 240 mv and full response to the vr. Exactly the same on both left and right channels...
Click to expand...

What is the voltage across any single emitter resistor (i.e., R01-R04)?
 
Leestereo said:
Adjusting the bias to ~75% of spec on DBT (100W) will often yield a bias close to spec on full AC.
Click to expand...
After a few minutes on the dbt and confirming no shorts, I have started switching to a inline current meter that measures real-time draw. I set bias while watching the draw and you can see if things are starting to run away. I started doing this after restoring a number of MAC’s. You set bias by watching main line draw on many MAC’s.
 
If you are wondering, I am retired and like to hear TOTL gear. I usually find dead or seriously abused notable pieces and bring them back to better than new condition. I am not a flipper and this isn’t my day job. Just a curious type with an obsession of sorts. I just about have this Luxman R1120 done and it is everything and more than the hype..upload_2022-4-7_20-31-35.jpeg
 
My G8000 vrs were backwards from the manual as mentioned previously on this post. You've really got a monster there. Enjoy.
 
jefferylhenr said:
If you are wondering, I am retired and like to hear TOTL gear. I usually find dead or seriously abused notable pieces and bring them back to better than new condition. I am not a flipper and this isn’t my day job. Just a curious type with an obsession of sorts. I just about have this Luxman R1120 done and it is everything and more than the hype..View attachment 2533925
Click to expand...
 
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