Got it working...kinda

VMilkRecords

Music Patrician
Sansui AU-7900 Repair and reconditioning.

So I got my sansui AU-7900 up and running. There's a slight issue...the modes. I don't know if it's supposed to be like this but, if I select normal the left speaker is louder than the left...way loud. You can't hear the other speaker unless you move the balance over and turn the volume up high.
When I select Reverse it just swaps places.
This isn't a problem with the channels since when I plug in my headphones the same thing happens.
I'm running it on mono right now and both speakers are working...but it's quiet compare to the other modes.
Might be a stupid question but...is this normal? I was under the impression that normal would be...you know..."normal".


thanks
 
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Hi.
I thought it wasn't normal.
First I tried it with my PC>ODAC>aux1 and then that's when I discovered the problem.
I tried it on Aux2 and the same thing happens.
After I made this thread I tried my turntable on phono 1 and it's still the same.
This is weird.
 
That points to a dirty mode switch ( or possibly input source selector switch or tape play switch). There are no active circuits in between the aux inputs and the mode switch, just wires and the two switches mentioned above.

Have you cleaned the switches?

You coud try operating the input source selector and tape play switches through their full ranges 10-20 times and see if this makes any difference

Cheers

John
 
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I haven't.
I have deoxit. This may come off as dumb too...but I don't know how to. Do I just spray it ontop of them? Or spray it between the gap?
I know I only give it short bursts.
 
I edited my prior post - see if switching the tape play and input source selector switches 10-20 times makes any difference.

Cheers

John
 
Steps

1
Purchase the right type of Deoxit for your application. Deoxit is manufactured in over a dozen varieties, so you should read carefully about the uses of each type before your purchase. For cleaning and lubricating potentiometers ("pots") or contacts, the standard "D5" spray should be used. Other formulations are available for more specialized applications, though, such as cleaning gold or conductive plastics.

2
Remove the case from your receiver or amplifier. To access the pots, you will have to remove the case. This can usually be done by removing a few screws on the underside of the unit. Remove these screws carefully and set them aside. Slide the case away from the chassis of the receiver. To access the pots, you only need about 1 inch (2.5 cm) of room behind the faceplate.
3
Locate the potentiometers. Just behind the knobs on the faceplate (the ones that control volume, tone, balance, et cetera) you will find the pots. The pots are small cylinders that are controlled through the knobs. Each pot should have a small rectangular hole that allows access to the internal components.
4
Spray the Deoxit into the first pot. Attach the long, straw-shaped nozzle to the can of Deoxit and place the tip of this nozzle into the hole in the pot. Spray a small amount of the cleaner into the hole and remove the nozzle.
5
Rotate the knob attached to the pot repeatedly. After spraying the cleaner into the first pot, turn the control back and forth repeatedly from its minimum position to its maximum position. This will spread the cleaner across the inside of the pot and help work loose any corrosion or dirt. Do this for about 2 minutes continuously. Repeat this process with each pot in sequence.
6
Allow the Deoxit to dry. After cleaning each pot, reattach the receiver's case. Allow the unit to sit for an hour so that the Deoxit dries sufficiently. Plug the unit in and test it. The knobs should now rotate smoothly and no distortion should be audible when rotating each control.
 
I tried fiddling with the knobs....no luck.

Do I really need to take this thing apart? I really don't trust myself doing that.
 
You are gonna have to tear it down to get to the input/output jacks on the back. This is likely where the problem is. There will be some cracked traces where the jacks solder on the board. Very normal for these.
 
Another possible and frequent trouble source is the "switched/un switched" slide switch located on the rear panel. Shoot some deoxit in there and slide it back and forth 10+ times. Most of my Sansuis have had issues here.
 
You are gonna have to tear it down to get to the input/output jacks on the back. This is likely where the problem is. There will be some cracked traces where the jacks solder on the board. Very normal for these.

Are you sure? Remember, the headphone acts the same too. Does that still point to the input/output jacks?


Another possible and frequent trouble source is the "switched/un switched" slide switch located on the rear panel. Shoot some deoxit in there and slide it back and forth 10+ times. Most of my Sansuis have had issues here. [/QUOTE said:
I tried doing that. I may try again. Looks like I'm getting nowhere with this :(
 
The headphones are a pick off from the power amp section.. not a separate amp from the pre-out...
 
AND have you tried your audio source direct into the power amp in ? Warning start with the gain WAY down on your source and speakers off until hook up is complete…
 
Your You tube video seems to prove the speakers & power amp are cool and your "ISSUE" is in the pre amp stage… not uncommon for a transistor to give up the ghost…

ALSO ( a sideways test ) if you feed there AUX IN and take a pair of RCA's and jump from REC OUT into the main in ( power amp ) this will disprove / prove that the RCA jacks/PCB internal of the unit are fubar…It's straight wire ( with a switch ) from those 2 points...
 
Are you sure? Remember, the headphone acts the same too. Does that still point to the input/output jacks?
:(

Oh yes. Pretty sure, but I cannot make a direct claim that this is the problem, because I have not proved it on my bench, but I have worked on several of these :)

Check all the solder joints for all the jacks on the back.
 
If you do the REC out to MAIN in.. That will prove Many Moons point,, which I think is a high probability and a 2 second test.
 
OK ( UNIT OFF )
1) From your audio source.( start with the volume way down ) . plug that in to AUX-1.
2) On the pre main switch select "separated".
3) Grab a stereo RCA patch cord and patch from REC OUT to MAIN IN.
4) Power unit up.. listen & report back..

Clearer?
Cheers
Mike
 
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