bhuskins
Super Member
I found a really nice 4000 that I've started to restore.
It'll eventually get a full recap and such but before I do that I always try to get the unit working with 100% functionality first.
All the inputs work great and output is strong and clear
All the controls have been cleaned...including the ones on the back
AM tunes perfectly with nice signal deflection and clarity
FM tunes great as well with nice strong signal and tuning deflection and a good quality sound and performance.
Spot on pointer dial alignment for both Tuners
The issues are:
-FM does not tune stereo even though a strong signal is received and sounds very good, no matter what VR401 (mpx adjustment on mpx board) is set to
-FM muting will not engage to mute static, no matter what adjustment is set to
--As a result, no difference in sound when MONO is selected and no difference in sound when the MPX filter is engaged. Also, no stereo light illuminates either (the bulb has been replaced)
I have spent most of my effort on the MPX board (Sansui Board F-1185.) I went ahead and replaced all of the electrolytic capacitors because I had them on hand and I also replaced the 6 transistors that are on the board. I used KSC1845/KSA992 for these. I have not replaced TR407 which is underneath the chassis but I don't think it is the issue because of the muting problem and lack of change to the sound when VR401 is adjusted...it causes no change in the sound no matter where it is adjusted to. I removed and cleaned VR401 and tested it. It tested fine and adjusts from about 5 ohms to about 9.5K ohms. I have not replaced CR401 and CR402 which look similar to orange dip caps but have three legs.
So, I'm at a bit of a loss as to where to look next. It's like the MPX board isn't doing anything no matter what its adjusted to. Pretty frustrating when the FM tuning is spot on and strong and the board doesn't have any IC chips.
Thoughts from the experts?
It'll eventually get a full recap and such but before I do that I always try to get the unit working with 100% functionality first.
All the inputs work great and output is strong and clear
All the controls have been cleaned...including the ones on the back
AM tunes perfectly with nice signal deflection and clarity
FM tunes great as well with nice strong signal and tuning deflection and a good quality sound and performance.
Spot on pointer dial alignment for both Tuners
The issues are:
-FM does not tune stereo even though a strong signal is received and sounds very good, no matter what VR401 (mpx adjustment on mpx board) is set to
-FM muting will not engage to mute static, no matter what adjustment is set to
--As a result, no difference in sound when MONO is selected and no difference in sound when the MPX filter is engaged. Also, no stereo light illuminates either (the bulb has been replaced)
I have spent most of my effort on the MPX board (Sansui Board F-1185.) I went ahead and replaced all of the electrolytic capacitors because I had them on hand and I also replaced the 6 transistors that are on the board. I used KSC1845/KSA992 for these. I have not replaced TR407 which is underneath the chassis but I don't think it is the issue because of the muting problem and lack of change to the sound when VR401 is adjusted...it causes no change in the sound no matter where it is adjusted to. I removed and cleaned VR401 and tested it. It tested fine and adjusts from about 5 ohms to about 9.5K ohms. I have not replaced CR401 and CR402 which look similar to orange dip caps but have three legs.
So, I'm at a bit of a loss as to where to look next. It's like the MPX board isn't doing anything no matter what its adjusted to. Pretty frustrating when the FM tuning is spot on and strong and the board doesn't have any IC chips.
Thoughts from the experts?