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Sansui G7500 HELP.

Overundr1 said:
The wiring looks correct from here as well. Anders, have you checked each of the output mounting boards for shorts between the traces and also possible hairline cracks in any of the traces? A while back I had to make a transistor mounting board from scratch out of perfboard to eliminate this very issue. The more suspect of the two is the left board. Now that I think of it I think Kevzep had to do the same thing once. Although this board also had the emitter resistors mounted you can get the general idea. Not hard to do.
Click to expand...

is there a short just above where the brown wire is burnt ? pic on post 275 .
 
anderslober said:
I hope this helps......please check the pics. I am staring myself blind...maybe one of you can see whats wrong..........pic 3 is good...there you can see the big caps, all the colored wires and the output config. BCE-BCE/BCE-BCE.

That is the original config. 2sc2581-2sa1106/2sa1106-2sc2581. They are BCE.
Click to expand...

white and grey wires look reversed on pic 4 sc left...also blue and yellow sa right pics on post 269
 
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Pete...they are supposed to 'crossover' like that in order to work the same way on each side.
Anyway...I just changed all 4 outputs to brand-spanking new ones...the tr legs are almost hard-wired to the pins....checked everything......still pulsating dbt................

I am flat-out out of ideas. Checked the resistors....checked the outputs.....checked the tr's...........nothing is burnt.......crap.....I dunno'.

Are we ABSOLUTELY sure it is in the output section??????

What about in the main power section???????? What does the IC ha12002 do? Protection?
 
anderslober said:
Pete...they are supposed to 'crossover' like that in order to work the same way on each side.
Click to expand...
ah sorry i am with it now ..i haven't been up long . was looking at board traces rather than the transistors .
how is it next to the brown wire that i pointed out ? maybe just the pic but looks possible short
 
got me stumped ..if all components are good .everything wired correctly ..no shorts ..
what can be wrong ?
is bias current set to zero ?
 
anderslober said:
Pete...they are supposed to 'crossover' like that in order to work the same way on each side.
Anyway...I just changed all 4 outputs to brand-spanking new ones...the tr legs are almost hard-wired to the pins....checked everything......still pulsating dbt................

I am flat-out out of ideas. Checked the resistors....checked the outputs.....checked the tr's...........nothing is burnt.......crap.....I dunno'.

Are we ABSOLUTELY sure it is in the output section??????

What about in the main power section???????? What does the IC ha12002 do? Protection?
Click to expand...

That is correct Anders - dedicated protection IC - commonly used, but unobtanium now I think.
 
petehall347 said:
is bias current set to zero ?
Click to expand...

That is NOT the problem here......We have been following and working with Anders on this since the start, Overundr1, Hyperion and I are very very familiar with these amps, and at this point we need Anders to be concentrating on information we are giving him thanks Pete, it just confuses things when too many people are throwing ideas into the mix, especially when they are rudimentary things which have already been ticked off the list hundreds of posts ago...
With these amps, if the bias is set too high, they have a catastrophic failure....

Anders, what frequency is the pulsating IE; how many times per second?

Believe me, it has to be something important to interrupt my watching the Formula 1 (Hungary Free practice 1)....But, I am seriously studying this circuit and looking at the pictures you took....
Now, could you do one thing and see if you can take a picture showing the positions of the driver transistors from the component side of the driver board......
 
Hyperion said:
That is correct Anders - dedicated protection IC - commonly used, but unobtanium now I think.
Click to expand...

Yeah, they are well unobtainium..........I dont think this is the problem though, but he has the one on the other board as a spare.....if needed.....
 
anderslober said:
Are we ABSOLUTELY sure it is in the output section??????

What about in the main power section???????? What does the IC ha12002 do? Protection?
Click to expand...

The protection circuit wouldnt have enough effect on anything to pull that kind of current.....

Lets where the positions of the drivers are.......and go from there......
 
Pictures of the drivers........I have checked them too......thrice.....all test good.
The freq. of the pulsing is about 2/sec............
 
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I am sticking to my guns at this point---

Remove the four outputs once again (I know I know)
Support the two output boards safely to prevent shorts, tape them down to a piece of cardboard if needed so they are stable (and safe to measure)

With power off and main caps discharged check for continuity between each mounting point just like you test a transistor out of circuit, there should be no continuity.
Turn on unit while on dbt, should NOT pulse
Measure b-c-e voltage for each transistor mounting point to ground
Report back with findings, left channel board and right channel board.
Hold off re-installing the outputs, there may be other measurements based on the results above.
And as always this step is prefaced with (please) :)

The HA1002 is another issue entirely and not related (yet)

-Lee
 
Ok Lee.........you want me to remove just the outputs from the 2 boards right? All four?
Then test continuity of the 'empty' holes.....there should be none.

Then power ON ......WITHOUT the main outputs in...........and measure the bce holes?

Ok...will do.
 
Lee...now you are sure it is ok to power ON(with dbt) without the outputs in?

I tried doing the 6-way tr test on the holes....to me.......there was continuity a couple of places.................what am i doing wrong?
 
anderslober said:
Lee...now you are sure it is ok to power ON(with dbt) without the outputs in?

I tried doing the 6-way tr test on the holes....to me.......there was continuity a couple of places.................what am i doing wrong?
Click to expand...

Please give details of where you saw continuity - dead short?... or something different - please specify...
 
I de-soldered all four outputs.......and then I put the probes in the holes.....meter set to diode test........0.38........1.993.....OL...OL.......WHAT am I supposed to see?

Anyway......shall I power up on dbt without the outputs? Will that be ok? If bright then dim......then we have narrowed it to the outputs/boards....is this correctly understood?
 
At work without schematic, however could you test with meter set to continuity not diode check. There may be some interaction between test points however there should not be a dead short.
 
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