Sansui 5000A FM issue

anti-doom

Well-Known Member
My Sansui 5000A has FM issue while all other functions work fine. The 5000A picks up FM stations fine but no FM when I press "FM Stereo only", depress that button then FM is back but volume is low (only 50% compared to other inputs). The tuning meters do not work either. While on AM mode, it has loud cracking noise when tuning among the stations but at least it works. Please help me to track down the issue or where to look at. FYI, I got 12V at F-1219 board as stated in schematic. Thanks a lot.
 
The crackling while tuning the AM section could be poor contact in the tuner VC with the ground bushings on the shaft, or possibly even slight interference between the VC plates. If the tuner VC has been thoroughly cleaned and properly lubed, that might minimize or eliminate the issue.

Regarding the FM "stereo only" feature, I have looked at the diagram and quite frankly do not understand the purpose of the feature. It appears to selectively mute anything which does not have a strong pilot signal and two distinct channels, so stereo separation adjustment may affect its performance. Again, this is merely a guess.

What is apparent is that when a stereo signal is detected at TR407 the function switches TR404 - For some reason.
 
The tuning meters MAY indicate a malfunction of the stereo circuits, and if they don't work, most receivers "mute" the output.

Another thing is if the receiver is not tuned "on center" of the station OR there is a mis-alignment of the "discriminator" coil, again you will get "muting" when switching to stereo.

Mark T.:music:
 
Thanks for the inputs. So the problem is on the FM-MPX board F1006A right? Where/what should I look at/for? Please help.
 
I am assuming you have NO electronics trouble-shooting experience at this point. so I will keep it as simple as I can so as not to "get you into deeper water"

Try watching the meters as you "tune through" a known strong STEREO station and see that-

A) The center channel meter moves from center or may "peg" at one side as you tune (look for any action).

B) See if the signal strength meter moves upward as you "pass" the station (look for any action).

If you get NO action on these meters, DON'T ADJUST ANYTHING!, the circuits in the stereo section are without power or an IC chip maybe bad, more help may be coming from other members'

The only thing you can safely try is spraying the SELECTOR SWITCH with contact cleaner (and working it back and forth) contacts to see if it "brings" anything "back to life" regarding the meters.

If the "STEREO" position of the switch has an oxidised contact it may "appear" that the stereo circuits may be bad.

Mark T. :music:
 
The signal meter MAY be defective (stuck or open circuit).

Does the "center channel" meter move when tuning across an FM station?

Mark T. :music:
 
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