Sansui G7500 HELP.

[kevzep]

Just checked the diodes....DOT with black probe....and red probe on the other...1.4V...otherway 'OL'. Both sides. Diodes are OK.

Phew!! Thank goodness for that.....:thmbsp:

So now make sure the dot corresponds to the R37/38 on each channel.....
This will make it the right way....

But now we have another problem which is, where is all the current coming from to burn those driver emitter resistors.....

We need to check those driver transistors.......:yes:

 

[anderslober]

i checked them.....drivers ok....pre-drivers ok. Kevin....the way it has been wired up until now, is as you say, but it has not been working. The very, very first post has a picture where the black wire is inwards......and it did work then for a while....remember? The unit came to me with the black wire inward..................and I did get it working with this config......until the outputs blew when I increased the volume. BUT, it did work.
SO, I think the black wire(cathode from diode) goes inward. Sansui scat and trace are different......makes everything easy...........NOT!

 

[anderslober]

KEVIN....I just downloaded the SM for the G7700..(similar design)..........the scat and trace are the same here............like I say. R38 hooks up to ANODE. Check it out.

 

[kevzep]

i checked them.....drivers ok....pre-drivers ok. Kevin....the way it has been wired up until now, is as you say, but it has not been working. The very, very first post has a picture where the black wire is inwards......and it did work then for a while....remember? The unit came to me with the black wire inward..................and I did get it working with this config......until the outputs blew when I increased the volume. BUT, it did work.
SO, I think the black wire(cathode from diode) goes inward. Sansui scat and trace are different......makes everything easy...........NOT!

Yes but thats why it blew up when you increased volume, because the diodes were the wrong way and couldnt regulate the current......

The cathode must go to the resistor.........

 

[anderslober]

Kevin check post 364. Compare the scats of the G7500 and the g7700....................WHICH one is the correct scat?????????????

 

[anderslober]

I think it blew up because of fake main outputs.

 

[kevzep]

Kevin check post 364. Compare the scats of the G7500 and the g7700....................WHICH one is the correct scat?????????????

HAHAHA typical of Sansui eh??.........now we are getting somewhere..........Standby Anders, I will be back soon......in millseconds....:thmbsp:

Hang on, this is getting confusing.......

 

[kevzep]

I think it blew up because of fake main outputs.

Yes, it did Anders, you are quite correct, those fakes would have worked at idle possibly but as soon as they need to swing any voltage its all over......

 

[kevzep]

Anders, the G7700 is the same, they have just put the trimmer in a different place, but the Cathode still goes to the NPN pre driver.....the Anode goes to the PNP pre driver.......

What you need to do is follow the trace on the circuit board to confirm where it connects to....
This means the 7500 and 7700 driver boards are slightly different, and Sansui may have even changed this during production.....

It appears I am telling you what is correct for the G7500 and you are telling me what is correct for the G7700

Like I said above, you need to use the schematic to follow the circuit on the board and see which one you have........Man this line of Sansui is shocking for this sort of crap!!!

 

[kevzep]

....................WHICH one is the correct scat?????????????

It entirely depends on what version of F2980 board you have.......that small change they have made, makes it so easy to be fooled and hook that diode up the wrong way.....

It is conceivable you actually have a G6700 F2980 board......

 

[anderslober]

My brain is fried! I am going scat-psycho!

 

[kevzep]

My brain is fried! I am going scat-psycho!

Lets stick with it Anders.......

What you need to do is follow from R38 where the diode joins to the board>>>>>then R38 should go to the trimmer>>>>that trimmer joins to the COLLECTOR of one of the pre-drivers, now. Which transistor is it?

IF it is TR10 and it is a 2SC2071, the CATHODE will connect to the R38......

IF it is TR08 and it is a 2SA939, the ANODE will join to the resistor.......

See if you can get a picture so I can help you trace it.....the more eyes the better......

 

[anderslober]

Pictures of trace side.......

I have soldered the wires in the OLD way...........I will however change them back once we figure out what is correct.

 

[kevzep]

Pictures of trace side.......

I have soldered the wires in the OLD way...........I will however change them back once we figure out what is correct.

Okay, yes, I can see that the way it is there Anders, is correct, I can see the black (cathode) wire on the trace which goes to the NPN pre driver, so for future reference, that G7500 schematic is WRONG.....

Okay, so now, we have to fire it up on the DBT again, watch for those resistors getting hot.......
Bias trimmer wound all the way off, anti-clockwise.......

 

[anderslober]

Kevin...ok.....I am glad you agree......I was going crazy thinking about this. So....THE WAY IT IS NOW, IS THE CORRECT WAY...........black(cathodes) wires inwards......towards the 2sc2071, which is near the middle of the board. OK.

DBT coming up..........

 

[kevzep]

Kevin...ok.....I am glad you agree......I was going crazy thinking about this. So....THE WAY IT IS NOW, IS THE CORRECT WAY...........black(cathodes) wires inwards......towards the 2sc2071, which is near the middle of the board. OK.

DBT coming up..........

Yes correct..........:thmbsp:


Damn those schematics and a bizzilion different versions of boards....:thumbsdn:

Watch those resistors for getting hot.....:yes:

Have you checked the output transistors emitter resistors?

 

[anderslober]

The BIG white resistors...0.33 ohm/5w? I will check them..........

DAMN......this is difficult......different scats and such......my brain is having a melt-down...whats left of it anyway................I need a nap!

 

[kevzep]

The BIG white resistors...0.33 ohm/5w? I will check them..........

DAMN......this is difficult......different scats and such......my brain is having a melt-down...whats left of it anyway................I need a nap!

Yes, the big white ones.....

When you measure them, they will come up at about 0.8Ω on the meter....they will never read 0.33......
But if theres a problem you will see it, they will be OL or read very very high, in megΩ.....

We are nearly there Anders, hang in there...........:thmbsp:

 

[anderslober]

Checked the emitter resistors......all ok.......DBT'ed.........bright........VERY dim(good)!..I had it on for about 20 sec.......no smoke...........should I have it on a bit longer? I was staring intently at the innards......no smoking or browning.

I think we are ready for main transistor install..................whadya say..."""'

 

[kevzep]

Checked the emitter resistors......all ok.......DBT'ed.........bright........VERY dim(good)!..I had it on for about 20 sec.......no smoke...........should I have it on a bit longer? I was staring intently at the innards......no smoking or browning.

I think we are ready for main transistor install..................whadya say..."""'

Go for it Anders..........!!

But leave those output boards floating and not attached to the heatsink....make sure nothing shorts out.....