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Sansui Seven low volume on fm only

Oscar66

Oscar66

New Member
Hello All. I am currently working on a Sansui Seven replacing all caps and multiple transistors with a kit from Affinity for Artifacts. This is the 2nd Seven I have worked on . First one was completed without any major issues. The issue at hand is I am getting low volume on FM only. Volume on AM and all other inputs working fine. All pots and switches have been cleaned. I'm guessing may have low power to FM circuit board. Any help much appreciated. Thanks in advance.
 
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I can see they are tu ning in to stations ok. both meters function and I do get very faint volume when turned way up. I can faintly hear the stations coming in as Imove the tuning wheel.
 
Did you remove the cover to the FM tuning gangs and throughly spray them down on both sides with CRC contact cleaner? When I did that to my '78 Kenwood tuner the signal strength increased significantly, but it was clearly audible before doing that.

What are you using for an antenna, how did you attach it to the posts and which posts did you use (300 ohm or 75 ohm), and did you also ground the unit to the same outlet it is plugged into?
 
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Have not tried that, but the signal strength seems to be ok. I can see the strength meter go way up, almost to max and the tuning meter locking in to the center of meter.
 
Did you see these posts?, they are below this thread under "similar threads".

Assuming all your fuses are good, see first post.

Sansui Seven - very low sound output

I recently found a Sansui Seven receiver very cheap (around ten bucks). Its in great cosmetic shape, but my problem is I am only getting very low faint audio. Even when I turn the volume all the way up. Aside from cleaning the switches/pots does anyone have any other suggestions/input? Thanks...
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Sansui 5500 low FM output & FM mute button short

Hello everyone. I need some help please. I just bought a sansui 5500 receiver. Everything works pretty good all but the FM. The signal and tuner meters work great, but the FM stations will play good sometimes then it will go so low that you can hardly hear the music even with the volume level is...
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Take a look at this post on a S 7, looks like what you are talking about, with a solution.

Sansui Seven Tuner Power Supply

Hello everyone, I was listening to FM on my Sansui Seven, it suddenly went mute. Upon investigation, it happened to be TR002 on the power supply board which is a 2SD330. This supplies +12v to the Tuner section. The rest of the unit works fine. Many in the forum mentioned TIP31C or TIP41C as a...
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Unfortunately I didn't test fm before starting recap, but according to user it was working. I saw the tuning meters working properly so assumed it was fine. I have verified power to the tuner boards per the schematic. getting 12v on 2B on f 1450 board and 6V on 4C on f1387b fm mpx board. Not sure where to look next. Not seeing any other voltages on the schematic.
 
If the signal meter works normally, the RF and IF sections are fine. If the tuning meter works normally, the detector is fine. Issue is likely somewhere between the output of the detector and the selector switch. Looks like output of the FM detector goes through the MPX board, which also contains the muting circuits.

I'd verify proper voltage to that board first. Schematic calls for +23.5v at 4E per the schematic I'm looking at.


If thats good, check the voltages around the muting circuitry. If you have a signal tracer or a scope it should be pretty easy to confirm if you have normal input to the MPX board or not. If it goes in normal and comes out muted, you know its a problem on that board. Another clue that may indicate a problem on the MPX board is if the stereo light works. If that never kicks on, it makes me suspicious.
 
Thanks gadget. I'll check voltage on 4E. I'm pretty sure it's something on the mpx board. I noticed when I touched the base of tr406, I temporarily got sound. Thought maybe it was a bad solder connection and resoldered it. Still no sound. Could that transistor be the issue?
 
painttoad said:
look at everything you replaced and verify correct orientation.

you may get better help in the sansui subforum. click the 'report' button and ask a mod to move it.
Click to expand...
Thanks Painttoad. I verified orientation and any wires I may have removed. Compared to another Seven I worked on. I'll see about moving this to the sansui subforum
 
gadget73 said:
If the signal meter works normally, the RF and IF sections are fine. If the tuning meter works normally, the detector is fine. Issue is likely somewhere between the output of the detector and the selector switch. Looks like output of the FM detector goes through the MPX board, which also contains the muting circuits.

I'd verify proper voltage to that board first. Schematic calls for +23.5v at 4E per the schematic I'm looking at.


If thats good, check the voltages around the muting circuitry. If you have a signal tracer or a scope it should be pretty easy to confirm if you have normal input to the MPX board or not. If it goes in normal and comes out muted, you know its a problem on that board. Another clue that may indicate a problem on the MPX board is if the stereo light works. If that never kicks on, it makes me suspicious.
Click to expand...
Getting 22.9v on 4E. Close enough?
 
The problem sounds like the muting circuit is on all the time.

Couple of things. What happens if you push the muting button in?

It looks like getting to the bottom of the MPX board on the seven is not very easy.
If you can try and lift one end of R457 (I think) and see if that does anything.

s7fm.jpg

That is the base voltage to the muting transistors.
 
So I lifted one side of R457 and now fm works with muting button on or off. I suspected it was something with the muting circuit. I checked all the transistors on that board and they look normal. Not seeing any shorted.
 
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