Sansui G-7500 schematic needed

[anatech]

Hi All,
I have a Sansui G-7500 on the bench. One channel had shorted outputs and drivers. Now that I've replaced the dead stuff I'd like to set it up properly. The regulated power supply may need some attention as well. It was (poorly) serviced somewhere else before I got to it.
Does anyone have a schematic for this animal? I also need the bias current setting recommended by the manufacturer.

Thanks for any help - Chris

[1978chevyman]

Hi, did you ever find the schematic, i have a G7500, had the same problem, bad outputs in the right side, I pulled them, then the left side worked fine, i swapped the good outputs to the right side, the amp plays but is very distorted. By chance do you know what I am missing, I checked what I think are the drivers but cant find anything else bad. Thanks for your time

[anatech]

Hi 1978chevyman,
I managed to repair it and made a close guess as to the bias current. Customer was extremely pleased after he got it hooked up. It hadn't sounded that good before it blew again.

i swapped the good outputs to the right side

Never, ever do that. The only thing you can swap between channels are your meter probes and your 'scope probes.

Never swap good parts from one channel to the bad channel!

Don't do that! Did my message come through? I'm just tired of repeating this, it wasn't anything you said, except for "i swapped the good outputs to the right side". Made me see red.

All right. Obviously you are missing something very important. Let's start at the extreme basic stuff.

Did you clean the heat sink, transistors and apply new thermal compound and mica insulators? If you have not done this, stop and correct the situation. Make sure the outputs go back to their proper places on the correct channel. Let me know when this is done.

-Chris

[Tony]

Originally posted by 1978chevyman
Hi, did you ever find the schematic, i have a G7500, had the same problem, bad outputs in the right side, I pulled them, then the left side worked fine, i swapped the good outputs to the right side, the amp plays but is very distorted. By chance do you know what I am missing, I checked what I think are the drivers but cant find anything else bad. Thanks for your time

hi,

this could be a sign of one emitter resistor being open, (0.33 if i am right) distortion is due to the fact that the driver is delivering the ouput.

imho, these sansuis are great receivers...they use sanken output transistor parts,

i happened to own a g5000 once...

[1978chevyman]

yes, i installed them correctly, new HS compound, clean heatsink and all that. I admit , I am very much a rookie but I have seen many amps correctly repaired and I know some basics. I know it isnt good practice to swap from one side to the other but I planned on ordering a hole new set of outputs, I wanted to verify if there was any other issues and well, there is. I only played them for a few seconds, not even long enough to get warm, they are not shorted at this time. I can install them back into the left side board (the good side) but im not clear, do you want me to reinstall the bad pair as well? again, thanks for your help and patience with a rookie, Kevin

[Tony]

did you test those allegedly bad parts with a dmm?

[Bigred]

Hey Kevin,

No sense re-installing the bad pair. Tony made a good suggestion... check the .33ohm 5W emitter resistor(s). I'd change the drivers with the new outputs even if they checked ok.

[Tony]

Originally posted by Bigred
Hey Kevin,

No sense re-installing the bad pair. Tony made a good suggestion... check the .33ohm 5W emitter resistor(s). I'd change the drivers with the new outputs even if they checked ok.

yup, i had this marantz reciever that had those symptoms and true enough, one side had an open 0.33ohm resistor.

[1978chevyman]

Hi all and thanks again for the help and info, yes, I have a Fluke MM, no scope yet. Seems Tony was right on the money with the emitter. Found one I believe to be bad, again, I don't have a schematic so I am using the good side for reference. Three of the emitters are showing .6 and one shows 12.7. Upon closer inspection, I noticed a small resistor in front of the emitter that looked a little burnt in the middle. It showed 222.5 on the good side and 8.2 on the problem side. This one is marked Red Red Brown Black.
Again, please excuse my Rookieness but it has been 15 years since High School and I cant remember how to tell values on Resistors anymore.
Ok, now for the drivers, again, no schematic and very little expeirience but I believe they are the transistors mounted to small heatsinks right in front of the emitters, 2 per side,one is blue and one is black. They are both NEC's and each have 2 numbers, one says D381 & 2M88C. The next one 8536 & 2M81C. I havent been able to find any info on these except for other postings inquiring about where to find them. I could be wrong and these may not even be the drivers.
Oh and yes, check the first two bad outputs with a DMM, they are dead shorted, I was able to find actual Sanken replacements for the outputs on ebay, they are on the way.
Again, thanks for any help, Kevin

[1978chevyman]

to add to the previous post, I had an error, the NEC transistor is actually a B536. Did a little more research and found the PN's to be 2SD381 and 2SB536, they are the drivers and are turning out to be hard to locate. Also, I figured out my resistor is a 22ohm 1% and I think it is a 1/2 watt. If anyone has the drivers I need available for sale, let me know Thanks again, Kevin