Sansui G7500 HELP.

Ok...I am sure that the outputs are mirror-imaged, NPN-PNP-PNP-NPN. The driver tr's too. I will pull them today and test them. I will also pull vr2/vr4 and test. I am also sure the diode is hooked up correctly. I will also change R52/54 (220 ohmers) again. Are there other resistors in the vicinity that should be checked? R60/66? R72/78? R82/04?

I would check the Class A driver TR06, and also check TR08/10 which are the pre-drivers.....if any of these are breaking down under load it will cause the bias to skyrocket too.....

At this point, I am suspecting driver transistors.....it is possible that all the stress on the drive stage may have caused the drivers to fail.....But we will see....

Can you get a pic of the driver board showing the driver transistors and the numbers on them?
 
Hey Kevin.......2sb536 are the blue drivers......and 2sd381 are the gray drivers. Check post #293. Good pictures there. They are mirrored exeactly as on the left channel....I will check them though...also the pre-drivers.
The unit has ONLY been on dbt power during all this. NEVER real power. So do you still think some components could be stressed?
 
Hey Kevin.......2sb536 are the blue drivers......and 2sd381 are the gray drivers. Check post #293. Good pictures there. They are mirrored exeactly as on the left channel....I will check them though...also the pre-drivers.
The unit has ONLY been on dbt power during all this. NEVER real power. So do you still think some components could be stressed?

If there was enough current flowing to bake the driver emitter resistors, damage may have occurred to the driver transistors.....
Also, checking those pre drivers and class A drivers will eliminate them causing problems.....
 
Kevin....I have been looking at the stvh3 diodes. The symbol on the output-board is like this: ->|-. The 'dot' on the diode is mounted to the cathode end. NOW.....on the main board the symbol(on the scat) is like this: >>>|. The wire from the outpot board's cathode should go where? To the cathode end on the main board??? I need this confirmed.
 
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Kevin....I have been looking at the stvh3 diodes. The symbol on the output-board is like this: ->|-. The 'dot' on the diode is mounted to the cathode end. NOW.....on the main board the symbol(on the scat) is like this: >>>|. The wire from the outpot board's cathode should go where? To the cathode end on the main board??? I need this confirmed.

I see what you are saying there....Well the cathode should connect to R38.

How does it look on the other channel?
 
I have taken some pictures of the boards where you can see the hookup. LEFT cannel is yellow dot diode. RIGHT channel is green dot diode. The connection that I am concerned about is the wires on the main board.....are the hooked up correctly? To me it seems wrong..........but, this was how it was from original status. D03/D04 symbols on the scat point inwards to each other...cathode to cathode....>>>|...|<<<..........I think maybe the black wire should be on the cathode end............page 10 SM............................
Please have a look and confirm with scat.
 
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Kevin are you sure about that? Cathode to r38.? On page 10 SM the ANODE is connected to R38.........the cathode goes to c24/c28.

Anode end: >>>| : cathode end.
 
if the good channel is wired the same as the bad channel surely it is correct .? follow the dots from good channel see where they go then do same with bad channel ..assuming the components test good then logically the problem is somewhere else or things are testing good when they aren't .. yes it can happen ..
 
If I mounted that wrong.....I AM AN IDIOT!

Trace the cathode on the other channel back and you should find it will go to R37.....

That would then prove the cathode on the fault channel would go to R38.....

It would certainly make the bias run away if it was the wrong way round....
 
if the good channel is wired the same as the bad channel surely it is correct .? follow the dots from good channel see where they go then do same with bad channel ..assuming the components test good then logically the problem is somewhere else or things are testing good when they aren't .. yes it can happen ..

Yes thank you, but we have this, lets not get too many experts in here at once, this is when confusion happens and mistakes are made, thanks....


The printed circuit and the schematic I have correspond to eachother, Im 99%
sure that I am correct.
 
Anders, if you have it wired up like it is in the first post, then it is indeed wrong......:thmbsp:

This is good, I can see a good outcome....
 
Kevin.....in my SM.....the ANODE connects to R38. Do we agree on the symbol in post #349? Cathode is pointing inwards on the main board.

I think both diodes were hooked up wrong..............the pictures in post #348 should make it quite clear......black wire from output board is the cathode. The cathode is then mounted inwards(towards the center of the main board)...............ie. black wire inwards.
 
Kevin .....posts are crossing...I think the first post is the correct hook-up. Here is a picture of what I THINK is the correct hook-up. Please confirm....thanks.
 
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The scat and trace picture are different. On the scat the cathode hooks up to r38. On the trace picture the anode hooks up to r38. Go figure.......please take a good look.
 
Kevin.....in my SM.....the ANODE connects to R38. Do we agree on the symbol in post #349? Cathode is pointing inwards on the main board.

I think both diodes were hooked up wrong..............the pictures in post #348 should make it quite clear......black wire from output board is the cathode. The cathode is then mounted inwards(towards the center of the main board)...............ie. black wire inwards.

There is confusion here, looking at the circuit diagram the cathode goes to R38 and R37 on the other channel.....

Can you use your diode checker to test the diode, hopefully the meter has enough power....
We think the cathode is the DOT correct?
If it is, put the black probe on the DOT side, and the red probe on the other......You should see something over 1V maybe up around 1.8 V......
The other way, it should be OL.....

If it reads voltage both ways, it is bad......

This way we can confirm the polarity....then refer to the Schematic and confirm which way it needs to be hooked up......

ANODE >l Cathode
is the way it goes, and if you refer to the diagram the way I am telling you is the way it should go...

I do see what you are saying Anders, but just ignore that picture on the F2981, and make sure the Cathode on both channels goes to those resistors R37/38.....

If they were both the wrong way round its possible the diode may be bad, might as well measure it........
 
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Kevin ...check post #358. Scat and trace(page 10 sm) are different. I will check the diodes. I have tested the drivers and pre-drivers....all good.

Also the picture in post #357......is that the CORRECT method of hookup?
 
Just checked the diodes....DOT with black probe....and red probe on the other...1.4V...otherway 'OL'. Both sides. Diodes are OK.
 
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