Sansui BA-1000 Rebuild help and questions.

[Nashou66]

I am also a member of AudioKarma and started a thread on my rebuild of a BA-1000.

 

As many know the schematic and service manual are near impossible to come by. Anyone have one   ?

Here is my thread .

 

I made the mistake of rebuilding before taking voltages on the harness to the Vfets while installed and also more importantly when removed so I could make sure the rebuild voltages are on par

with the original with Vfets removed. This way i would be able to make sure the rebuild went well and I could reinstall them with out worry .

 

Here are the voltages I got with Vfet's removed after the build in this link .

 

https://live.staticflickr.com/65535/54306945470_4f749d8e4e_b.jpg

 

 

Any one have a BA-1000 they would be willing to possible remove the Vfet's and take the measurements to help me verify my voltages?

 

I know its a big ask but it help out a lot.

 

Thanks in advance

 

Athanasios

 

 

Edited February 4 by Nashou66

[Nashou66]

Adjusting the Bias trimpot adjusts the voltages on the Source pins of all the V-fets ( these are removed as of now).  The Gate and Drain pins are unaffected. 

 

Does this sound right or an indication I can re introduce the V-fets to the unit?

 

I used a translator and then edited the only parts of the service manual I could find images of. 

 

 

 

 

I attempted to make a board layout diagram from a photo of the bottom of the PCB. some traces are hard to see.

 

 

 

 

Edited February 4 by Nashou66

[Nashou66]

 

 

Edited Sunday at 07:52 PM by Nashou66

[Nashou66]

Looking at the two diagrams from the J-fet testing document floating around for testing Them and V-fets it shows a diode
for each fet .

So I decided to use diodes between the gate and source and in the direction shown in these diagrams shown below

N-Channel

 

And P channel





So I put diodes from source to gate with the cathode facing the direction for each channel type to mimic the V-vet more closely than a simple resistor. My thought process was that the source voltage would not contaminate the Gate voltage , now was this the correct deduction? Maybe not but I think it worked.

For the SK's I now get negative voltages and the SJ's I get positive. All Neg probes to chassis , positive on gates at the sockets .

FT701 2SK70 = -16 v

FT703 2SJ20 = +16 v

FT702 2SK70 = -13.5 v

FT704 2SJ20 = +14.8

As the amp was on longer the voltages got closer to each other on all four Gates .

Video showing my test .

 

 

 

 

 

 

Athanasios

[Nashou66]

I still can't find a schematic so I am attempting to make my own using the free web program on Digikey called Scheme-it .

 

NOt sure what I'm doing but Im giving it a shot.

 

this is how far I got so far.

 

 

 

 

I can  give the link to the project if anyone can cleaan that mess up for me lol

 

Athanasios