• The move to the new server is done. There are some software and database maintenance updates in process. This has us passing the hat around to help out. We appreciate any donations. Seriously, even a dollar helps. The payment page may be found here - https://www.audiokarma.org/support.html

Sansui BA-2000 bias adjustment

Hyperion said:
Please clarify.

These voltages are on the collectors of those transistors, with reference to ground (chassis)? with the unit not on DBT ?

This is directly across the zener with power applied and unit not on DBT ?
Click to expand...

Yes this was with the dim bulb on with positive probe to collector and chassis ground I used the negative speaker terminal actually for a good point.

The test for zener was across both legs with the dim bulb on

I’m going to assume you want these results without using the dim ?
 
quadmatrix82 said:
The zener diode continues to have 580mv
Click to expand...
There's your problem, the zener is faulty - it's behaving like an ordinary diode (or it is polarity reversed!), which is wrong, you need a 400mW or 500mW 13V zener as a replacement. (for polarity, the marked end of the diode should go to the 'fatter' trace (i.e. ground) on the board).

No need to remove any transistors for the time being, replacing the zener diode may solve all the issues. :)
 
Last edited:
I’ll change it and report back I have them here strange I changed it already shame it didn’t last long…the original probably would be still working!
 
Ok I had another look,

Tr604 was replaced with ksc2383y
Tr607 was replaced with mje15032g
Tr608 was replaced with mje15033g
Tr612 was replaced with ksa1013y
Tr616 was replaced with ksa992
Tr613 was replaced with ksc1845 note original 2sc1400 had much higher gain 800hfe vs 400hfe from memory.

What do we think about these substitutes?

These were all in play already and fresh so I didn’t pull and test them but checked all the tracks and soldering seemed good so left them

I noticed r647 470 ohm 3 watt had heat spots on the board measured out of circuit it tested low about 430 ohms. I replaced it with a new 5 watt 470 ohm resistor.

While I was there replaced d01-2 with 1n4148 it’s in close proximity and maybe they have been heat stressed too.

Anything else I should check before reassembling and testing?
 

Attachments

  • IMG_2136.jpeg
    IMG_2136.jpeg
    184.1 KB · Views: 2
  • IMG_2135.jpeg
    IMG_2135.jpeg
    115.6 KB · Views: 2
That's a good list of transistor substitutes, you can give it another try, but without testing those transistors all bets are off. The symptom you are seeing suggests to me that maybe TR604 or TR616 has failed, but it could be something weird like an 'open' resistor like R628 ?, Also please double check the orientation of C606 and C614.
 
I replaced tr604 and tr616 and same result unfortunately

R628 test perfect and orientation of the caps are correct

Looking at the zener diode it still measures at 580mv :(
 

Attachments

  • IMG_2137.jpeg
    IMG_2137.jpeg
    141.1 KB · Views: 3
quadmatrix82 said:
I’m starting to think is it possible there’s an issue with the board the filter caps screw to?
Click to expand...
A missing ground perhaps? - put an ohm meter on the ground trace of the PSU board and check that it is connected to the chassis, or any of the transformer secondary winding centre taps.
 
I measured from a few negative ends of the caps on PSU board to some screws in the chassis and there is continuity
 
So just to firm up on a few facts.

This regulator with replaced semiconductors has actually worked OK at some point? i.e. Have you checked the pinouts of the replacements IF the regulator hasn't worked since the transistor changes.

When did it stop working? - what operations have you performed on this regulator which might be relevant?

Have you actually checked all the transistors in the negative regulator, I know you replaced two, but what about the others?

If all of the above has been done, and we have eliminated missing grounds or other wiring faults, we are down to weird faults like leaky/shorted capacitors or open resistors - you have checked R621 (10Ω) & R622 (10Ω) recently?

The zener diodes you are using, are you sure they are zeners? - what is the type number written on the diodes themselves? - i.e. NOT from the supplier delivery note.

Assumption.
I am working on the assumption that as the negative regulator has the voltage reference in it (the zener) that it has to work before the positive regulator will come up, so I have limited my attention accordingly.
 
ok here goes with answering your questions

Hyperion said:
So just to firm up on a few facts.

This regulator with replaced semiconductors has actually worked OK at some point? i.e. Have you checked the pinouts of the replacements IF the regulator hasn't worked since the transistor changes -
the symptoms are the same before and after the change - I did not check the original voltages, the pin out can’t be wrong as it’s mounted to the heatsink. The originals were heat stressed but tested well with my transistor tester. The new ones have never worked any better than the old ones from what I can tell.

When did it stop working? - what operations have you performed on this regulator which might be relevant? Stopped working around November initially I thought the speaker was faulty but when I swapped amps out I realised it was the sansui at fault the distortion is worse as you increase volume I will test more voltages tomorrow

Have you actually checked all the transistors in the negative regulator, I know you replaced two, but what about the others? I checked them all they are new and test good I followed the board for pin out implementation I can take more photos if needed
Click to expand...

Tr607 e 7.2v c 67.2v b 7.8v
Tr616 e 0.6v c -6.6v b -1.2v
Tr603 e 66v c 20v b 66v
Hyperion said:
If all of the above has been done, and we have eliminated missing grounds or other wiring faults, we are down to weird faults like leaky/shorted capacitors or open resistors - you have checked R621 (10Ω) & R622 (10Ω) recently? These are fuse resistors they are testing well and were replaced manual says 470 ohm schematic says 10 ohm I fitted 10ohm.

The zener diodes you are using, are you sure they are zeners? - what is the type number written on the diodes themselves? - i.e. NOT from the supplier delivery note. I am sure these are correct the previous one which I replaced worked fine for years and new one installed is bzx55b-13-tr 13v zener 500mv 2 percent tolerance

Assumption.
I am working on the assumption that as the negative regulator has the voltage reference in it (the zener) that it has to work before the positive regulator will come up, so I have limited my attention accordingly.
Click to expand...

In addition to my comments I found r639 470k to read low approx 430k out of circuit so I replaced it I have now replaced also d610-614 with 1n4148 and the 27v zener to rule any other diodes out.

I can’t find any other bad resistors or broken wires on the power supply board.

Tr616 doesn’t seem to be on and where the issue lies?
 
You must log in or register to reply here.
Back
Top Bottom