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Old 2nd September 2012, 09:05 PM   #1
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Default Sansui help please?

Hello all. I have a sansui 350 sold state amp. I replaced the power caps and my amp is still running hot on the A channel. The B channel is still pretty cool. The transistors are really getting hot in about a 1 min. after you turn the amp on. Also putting new power in caps didn't take care of the leaking (D.C. voltage) coming out of each speaker input. I have 4 so its a total of 23.7 with the old caps and now with the new caps in its 22.1 so 22.1*4=88.4 D.c. volts now coming out. Not good. Is there anyone who can help me out there? I just want my amp fixed so I can use it. Thanks jm
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Old 2nd September 2012, 10:52 PM   #2
amptech is offline amptech  Scotland
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Hello, your amp has gone dc and replacing filter caps will not correct this fault...
What your need to do is get the circuit diagram or take voltage checks from the working channel. If possible cut the supply feeds to the faulty channel so you can take voltages such as ht v and so on, also check the mv reading across the emitter resistor on the o/p transistors. Post a photo of your amp on here so we can give more infor.
Between each channel is there fuse?

Check at the long tail input small transistors then vas stage etc...

Don't load the faulty side as yet, normal readings will be say in the milli volt range between say 30mv or so.
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Old 3rd September 2012, 09:32 AM   #3
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Have you done any cold check within the amplifier stage and looked for cracked tracks or loose component leg's.....
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Old 3rd September 2012, 11:43 AM   #4
RJM1 is offline RJM1  United States
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The Sansui 350 output is cap coupled. If you have DC on the output replace the output capacitors C817, C818 (1000F 35V).
Although you will have DC across the output with no load hooked up. Try placing a 1K resistor across the speaker outputs and measure the DC again.

Almost usable schematic available here.
http://akdatabase.org/AKview/display...157&fullsize=1

Last edited by RJM1; 3rd September 2012 at 11:51 AM.
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Old 3rd September 2012, 12:14 PM   #5
Mooly is offline Mooly  United Kingdom
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It sounds as though the amp works but runs hot... yes ?

Thanks to RJM1 for the circuit

First, measure the volt drop across the two circled emitter resistors on the output transistors and then set the preset pot on the hot channel so that the voltage across the resistor is similar to the cool channel one.

It might be a good idea to replace the preset as they tend to go intermitent after many years. Also a "bulb tester" in series with the mains might be a good idea to avoid mishaps.
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Old 3rd September 2012, 01:04 PM   #6
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Quote:
Originally Posted by amptech View Post
Have you done any cold check within the amplifier stage and looked for cracked tracks or loose component leg's.....

No But, I will look again.
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Old 3rd September 2012, 01:05 PM   #7
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Originally Posted by Mooly View Post
It sounds as though the amp works but runs hot... yes ?

Thanks to RJM1 for the circuit

First, measure the volt drop across the two circled emitter resistors on the output transistors and then set the preset pot on the hot channel so that the voltage across the resistor is similar to the cool channel one.

It might be a good idea to replace the preset as they tend to go intermitent after many years. Also a "bulb tester" in series with the mains might be a good idea to avoid mishaps.

Okey I will try that. I do have the circuit lay out. Thanks jm
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Old 3rd September 2012, 01:08 PM   #8
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Quote:
Originally Posted by RJM1 View Post
The Sansui 350 output is cap coupled. If you have DC on the output replace the output capacitors C817, C818 (1000F 35V).
Although you will have DC across the output with no load hooked up. Try placing a 1K resistor across the speaker outputs and measure the DC again.

Almost usable schematic available here.
AK Database PDF Gallery: Click image to close this window


So I already replaced both of the 35v @ 1000uf output capacitors last week. Now the D.c. volage droped by one number and some. So it's not 23.7 It's 22.1. I will have to dig deeper I hope this does not cost alot.Thanks jm

Last edited by cross reference; 3rd September 2012 at 01:10 PM.
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Old 3rd September 2012, 01:12 PM   #9
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Quote:
Originally Posted by amptech View Post
Hello, your amp has gone dc and replacing filter caps will not correct this fault...
What your need to do is get the circuit diagram or take voltage checks from the working channel. If possible cut the supply feeds to the faulty channel so you can take voltages such as ht v and so on, also check the mv reading across the emitter resistor on the o/p transistors. Post a photo of your amp on here so we can give more infor.
Between each channel is there fuse?

Check at the long tail input small transistors then vas stage etc...

Don't load the faulty side as yet, normal readings will be say in the milli volt range between say 30mv or so.

There are 2 fuses in the back and I replaced them a year ago. If the fuses were bad the amp would not turn on. I don't think there is a fuse for each channel but, I will look again. Also the A channel is always on the hot channel. The cold channel I have to push the switch on for both channels to be running at the same time. I will try to put some pictures up I had a hard time doing this before. jm

Last edited by cross reference; 3rd September 2012 at 01:14 PM.
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Old 3rd September 2012, 01:26 PM   #10
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what you are doing is not proper troubleshooting ...the advice was given to check all voltage according to the schematic ....

proper repair cannot be based on speculation ...proper repair is to be based on procedure

real reasons for overheating :
there is both bias and symmetry trimmers inside the amp these both circuits need be both working and adjusted properly

there is a good chance the one of the outputs is shorted verifying voltage according to the schematic will explain both
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