Hi!
I got a little Sansui TU-555 tuner. When I first got it reception was very weak and no stereo. A lot of caps were bad so I started by changing them, touching up the soldering and replacing the famous 2sc458 transistors. The result was slightly better reception. I than cleaned the local/dist switch on the back and now reception is great only it doesn't decode stereo : I checked and double checked the orientation of the caps I changed, tested the 4 transistors on the multiplex circuit that are fine, changed the trimmer resistor, cleaned the remaining switches but there's no improvement. When I turn the trimmer resistor clockwise all the way I have a faint glow from the stereo bulb when tuning to stereo stations but when I listen to it it's clearly still mono...
I got a little Sansui TU-555 tuner. When I first got it reception was very weak and no stereo. A lot of caps were bad so I started by changing them, touching up the soldering and replacing the famous 2sc458 transistors. The result was slightly better reception. I than cleaned the local/dist switch on the back and now reception is great only it doesn't decode stereo : I checked and double checked the orientation of the caps I changed, tested the 4 transistors on the multiplex circuit that are fine, changed the trimmer resistor, cleaned the remaining switches but there's no improvement. When I turn the trimmer resistor clockwise all the way I have a faint glow from the stereo bulb when tuning to stereo stations but when I listen to it it's clearly still mono...
Do you have an antenna connected to the tuner? How far away are the stations?
What is the function of the trimmer?
What is the function of the trimmer?
Yes I have a standard 75ohm T antenna connected. Some are quite local others a little further but I perfectly receive them with all of the tuners and receivers I have/had.
I don't have the alignment procedure for this model and had no luck finding it, might be to set the 19KHz signal. I do have a schematic but it's slightly different from what I actually have in front of me.
I don't have the alignment procedure for this model and had no luck finding it, might be to set the 19KHz signal. I do have a schematic but it's slightly different from what I actually have in front of me.
Well my perseverance paid off : I started scoping around the mpx circuit and I found out that the signal was lost at TR402. It turns out this transistor was installed correctly according to the markings on the board but when I actually followed the traces I found that the collector and emitter were going to the wrong components. I turned the transistor around and it now perfectly detects and decodes stereo. The person I bought this from told me stereo never worked and the solder joints were 100% original (even had the color markings on the bottom often found on sansui gear) so this was a factory error !!! I wonder how this got through quality control !! 😱