02-20-2015, 10:33 PM
Well, since I have (more or less) managed to get my 700-T going, I decided to revisit my 440-T.
It has heavy distortion in both channels, which I have traced to...the control amplifier board. Both channels go into the control amplifier clean, and come out dirty.
So I've pulled the control amplifier board from a 550-T junk set I have, and will do the same thing with it as I did with the board I put into my 700-T, and that is to replace all of the electrolytics and the 0.33 uF film caps. I will also go over every solder joint on the board, as I did with the 440-T board which I put into my 700-T.
As for the multiplex decoder...
I built a prototype multiplex decider based on the LM1310 chip, and temporarily installed that perfboard in this 440-T. It seems to work...at least, I can tell a difference between FM stereo and FM mono...but it does not produce sufficient voltage to light up an LED stereo indicator. And I hooked everything up according to the schematic I found online for the circuit used with this IC. ?????
However, since then I discovered that the original Fisher multiplex decoder board that was in this 440-T is the same board used in the 220-T. I have the 220-T service info, so if I have to go back to original, at least now I have some voltages on the 220-T schematic which I can use as a reference.
It has heavy distortion in both channels, which I have traced to...the control amplifier board. Both channels go into the control amplifier clean, and come out dirty.
So I've pulled the control amplifier board from a 550-T junk set I have, and will do the same thing with it as I did with the board I put into my 700-T, and that is to replace all of the electrolytics and the 0.33 uF film caps. I will also go over every solder joint on the board, as I did with the 440-T board which I put into my 700-T.
As for the multiplex decoder...
I built a prototype multiplex decider based on the LM1310 chip, and temporarily installed that perfboard in this 440-T. It seems to work...at least, I can tell a difference between FM stereo and FM mono...but it does not produce sufficient voltage to light up an LED stereo indicator. And I hooked everything up according to the schematic I found online for the circuit used with this IC. ?????
However, since then I discovered that the original Fisher multiplex decoder board that was in this 440-T is the same board used in the 220-T. I have the 220-T service info, so if I have to go back to original, at least now I have some voltages on the 220-T schematic which I can use as a reference.
--
Ron Ramirez
Ferdinand IN
