sansui G7500

trace59 · 21st November 2007, 06:51 AM

I am an experianced electronics technician. I ran a business for 7 years and worked for others for 10 years. I have been out of the swing of things for about 7 years. I recently have come across a Sansui G7500 that had the right channel shorted out and several parts(resisters( burned on the amplifier board. I have the schematic and it apears to be miss marked. I bought original outputs and they shorted as soon as I powered it up. I tried a second time with a variable ac supply and it shorted afetr about 40 VAC.

Now I have spent a lot of time on this and I am at a loss, I can find no obvious problem. I have noticed that the dc supplies +63 -63 volt supplies. won't go above 15 VDC, after reaching this voltage the current starts going up and the voltage starts going down. Do you have any ideas of what I am missing?

audiomachines · 21st November 2007, 07:44 AM

oscillation?.. could you post the schematics please.

Regards,
audiomachines

trace59 · 21st November 2007, 06:57 PM

schematic

trace59 · 21st November 2007, 08:59 PM

I attached the schematic on my last post, not sure where it is? here it is again

trace59 · 21st November 2007, 08:59 PM

evidently it is to big, lets try one more time.

trace59 · 21st November 2007, 08:59 PM

I am a new user and it seems I cannot email you, I do have the complete schematic on a PDF, but I can only post a small section. I can email it to you when I am allowed

audiomachines · 22nd November 2007, 04:06 AM

the schematic you posted is barely readable sir, in the meantime you could check for some 'open' resistors' especially those low values (100 ohms and below) some tend to go open.

You mention on your previous post that upon power up the output blows instantly, an open bias ckt perhaps? open bias diode/bias transistor, loose trimpot

trace59 · 22nd November 2007, 04:16 AM

I have checked all of the low ohm resister. I have also checked the bias Diode. I have the schematic on a 3.2m pdf and I can email it to with an address. I have not checked the trim pot. I will take another look at it this weekend.

audiomachines · 22nd November 2007, 04:19 AM

here is my email ad jade_808a@yahoo.com

trace59 · 22nd November 2007, 04:28 AM

I have sent you the diagram, There are misprints on it, the placement of the outputs are not marked correctly. Please look this over and I will get back on this thread tommorrow.

21st November 2007, 06:51 AM	#1
trace59 diyAudio Member Join Date: Nov 2007	sansui G7500 I am an experianced electronics technician. I ran a business for 7 years and worked for others for 10 years. I have been out of the swing of things for about 7 years. I recently have come across a Sansui G7500 that had the right channel shorted out and several parts(resisters( burned on the amplifier board. I have the schematic and it apears to be miss marked. I bought original outputs and they shorted as soon as I powered it up. I tried a second time with a variable ac supply and it shorted afetr about 40 VAC. Now I have spent a lot of time on this and I am at a loss, I can find no obvious problem. I have noticed that the dc supplies +63 -63 volt supplies. won't go above 15 VDC, after reaching this voltage the current starts going up and the voltage starts going down. Do you have any ideas of what I am missing?

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21st November 2007, 07:44 AM	#2
audiomachines diyAudio Member Join Date: Dec 2005 Location: silang, cavite	oscillation?.. could you post the schematics please. Regards, audiomachines

21st November 2007, 06:57 PM	#3
trace59 diyAudio Member Join Date: Nov 2007	schematic

21st November 2007, 08:59 PM	#4
trace59 diyAudio Member Join Date: Nov 2007	I attached the schematic on my last post, not sure where it is? here it is again

22nd November 2007, 04:06 AM	#7
audiomachines diyAudio Member Join Date: Dec 2005 Location: silang, cavite	the schematic you posted is barely readable sir, in the meantime you could check for some 'open' resistors' especially those low values (100 ohms and below) some tend to go open. You mention on your previous post that upon power up the output blows instantly, an open bias ckt perhaps? open bias diode/bias transistor, loose trimpot

22nd November 2007, 04:16 AM	#8
trace59 diyAudio Member Join Date: Nov 2007	I have checked all of the low ohm resister. I have also checked the bias Diode. I have the schematic on a 3.2m pdf and I can email it to with an address. I have not checked the trim pot. I will take another look at it this weekend.

22nd November 2007, 04:19 AM	#9
audiomachines diyAudio Member Join Date: Dec 2005 Location: silang, cavite	here is my email ad jade_808a@yahoo.com

22nd November 2007, 04:28 AM	#10
trace59 diyAudio Member Join Date: Nov 2007	I have sent you the diagram, There are misprints on it, the placement of the outputs are not marked correctly. Please look this over and I will get back on this thread tommorrow.

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