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Sansui 4000 zero voltage for bias adjust

T

thespclst

New Member
Hey everyone,

I recently recapped a Sansui 4000. Step one was adjusting the bias which should have been simple. I followed the service manual directions but when attempting to read voltage across f001 I am showing no voltage, even when turning the bias pot up. I have all the lights on and know there's power to the unit. When playing a source through an old set of 8ohm speakers I can hear audio(although it's low and distorted). Any ideas where to start checking?

Thank you very much,
Rob
 
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So just an update. I swapped both Drive amp boards(F-1150). Still no voltage on f001 or f001. I removed both F-1150 boards and now I'm getting voltage on f001 & f002. I'm assuming this means I have a problem with both driver amp boards?
 
How much voltage? Before you apply power again check components on the driver boards and the output transistors for shorts and bad resistance values. I am surprised you did not blow fuses if you had no voltage when the boards were in circuit. If so may be a bad connection from the power supply.
 
JRC75 said:
How much voltage? Before you apply power again check components on the driver boards and the output transistors for shorts and bad resistance values. I am surprised you did not blow fuses if you had no voltage when the boards were in circuit. If so may be a bad connection from the power supply.
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So I apologize for the confusion, I'm fairly new to all of this. So I do have voltage across f001 & f002. What I'm missing is the Milliamps across these points for setting the bias. The service manual does not indicate that resistance(speakers) or an input source should be applied to the reciever while adjusting the bias. So I did hook up some old speakers and use an ipod into the aux port to check it and still no reading in mA on my meter. I tested all the emmiter resistors and they are within spec. I pulled all the output transistors and checked them. The far right one does have a short in it. (Luckily I found some on the bay). Still I would think that in the left channel I would be getting some kind of reading. I can hear music through the left speaker but it's exteremely low and distorted.
 
What brand and model # is your multimeter? May have blow a fuse in the meter.
 
To make bias measurements and adjustments -- No source !! Volume at min. and no load .
 
When you tried measuring the milliamps across the fuses. Did you move the meters com test lead to the jack marked " 10A or µA/mA" ?
 
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Always start at the highest range and then lower the range as needed. Key is not to overrange the meters readout..
 
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avionic said:
Then you probably have to manually select the highest current range to start with. If you start with low range and there is more current there than the meter can handle at the lower range -- You most likely will blow a fuse in the meter. In a Fluke, these fuses are about $7 a pop.

Holy snikeys.. They have gone up in price..
http://www.mouser.com/ProductDetail/Fluke/FUSE-440MA-1000VB1/?qs=sGAEpiMZZMsIz3CjQ1xegUTP01/p1NmElLtlLNqj7fI=
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Well I did blow the 500mA fuse in my meter. I'll grab another one today and start in the 10 amp range first.
 
My Fluke 's don't autorange in the current mode operation. So I have to set them manually. I popped the fuse in my Fluke while working on my first 9090DB years ago. The fuses were $5 then.
Forced me to dig up my Fluke user manual ..Ah ha I said.
 
I had the same issue on my 9090, fuse was blown in the dmm.... Drove me crazy at first , but after replacing all was good!
 
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