Pioneer SX-600T early SS receiver - FM is quiet, and FM Auto does not work

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Hi folks. I have a Pioneer SX-600T. Mine is from 1966 and is in great shape but did not work when I got it. It smoked slightly and the main caps were leaking. I replaced the main caps, the bridge rectifier, and cleaned the controls. I was able to get FM out of the left channel but the right was very quiet and distorted. I recapped all the boards and now I have clean sound through the Aux input. AM is fine. FM mono and stereo are fine but are MUCH quieter than the Aux input, I mean way too quiet. FM Auto hums, and the hum changes with the volume. No reception at all. At this point I have replaced all the electrolytics and the oil caps, except the two caps on the AM board which I couldn't really get to and the two 100 uf 150v caps underneath that I have to order. There's a schematic for this but I don't have a service manual. Any thoughts?
 

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that schematic is really hard to read,but those caps you didnt change are filters for a dedicated power supply that serves the front end (B 130v) it would seem likely that the hum could be from that.that's pretty high voltage. despite all the transistors. it would seem like the radio portion of this set is tubes,yes? i couldnt find a schematic or any board data except a sales brochure
 
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i did manage to find a picture of the set with the cover off and indeed it has a VACUUM TUBE and thats why that B voltage is high,i dont know what that tube does do you have a tube number? its probably the oscillator.tubes can get week too.does the heater in the tube glow? and i might add that tube sockets oxidize like switch contacts and need deoxit too.without data that might be hard to trouble shoot.im only guessing but ill bet there are are resistors under that front end that might need checking too after you change the caps. and i almost forgot DONT FOOL WITH THOSE CAP"S UNTIL YOU DISCHARGE THEM
 
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The tubes are all 6CW4 Nuvistors. They have metal covers, but they do seem to get warm, so I think they're working. I'll get those caps and get back to you.
 
I replaced both of the 100 uf 150v caps, as well as the SM150A diodes next to them (with 1N4007 diodes). No change. I found a wire that had come loose from the FM multiplex board, as well as an unsoldered connection on another board, and fixed those. No change. I pulled all four of the 6CW4 nuvistors and tested them. They're all fine. No change.

For whatever reason, FM went up to full volume for a second at one point, then dropped back down. No idea.

The FM auto input is currently playing very faint crackling on the right channel and a decent hum that varies with volume, plus a louder crackling, on the left channel.
 
hmmm. its a shame the schematic doesnt give pin number's do you have 130v to the front end and do you have -12v to the if board and mpx board? the intermittent volume seems to suggest a bad connection issue.were you able to deoxit the tube sockets and pins? and that gang switch that supplies the -12v? its funny a friend of mine in Maine about a month ago offered me one of those,i may have to take him up on it!
 
I worked the tube pins back and forth a ton, so I'm pretty sure that's not an issue. I will Deoxit those however. I'll check voltages later today as well.
 
Sorry for the delay. The FM and multiplex boards only get power when the selector switch is on FM. When it's on FM, here are my results:

AM9127B board (left to right, from top)
AFC terminal -0.106v
-12v terminal is at -14v
Gnd 0
Mute -0.69v
Out is at -0.56v
AFC on right (from front) is at -0.55v

AM9125 board (left to right, from top)
Sepa -2.3v for both
-12v terminal is at -14v
Mut in -0.68
Mut left 0
Mut right -13.4v
FM in -0.58v
Relay -30.3v
+35 terminal at 30.7v

And the power supply (left to right, from underside)
0
-30v
-28.5v
-14.3v
0
-.046v (I think that's just what the meter reads when it's not doing anything)
 
Ok, this is stupid. If I put my finger under the FM MPX board ( second from the back) in the right spot I can make the relay clock and the radio starts working under FM auto. It’s still super-quiet though. I’ll take a few pics of the area tomorrow.
 
im not much help as i can only read your schematic and there's nothing i can find online. the relay appears to provide stereo when the mpx arms it.
 
on one of the terminal's on the front end this the plate voltage for the tubes. follow the schematic. it's source is those diodes and 100mfd caps you said you changed and a dedicated winding from the power transformer. its NOT shown as a WIRE but is REPRESENTED BY "B" on the schematic bottom and again at the fm front terminal unknown. DO be careful what you touch!!!! if nothing else un plug the set and trace the wires FROM those filter caps to the font end. AND remember that even unplugged those filter caps can hold a nasty surprise
 
I have 150v on the top 100uf cap and 140v on the bottom one. That one traces to the tubes, and I have 140v going into that section.

FM auto started working out of nowhere. With it working, measurements are:

AM9127B board (left to right, from top)
AFC terminal -0.66v
-12v terminal is at -14v
Gnd 0
Mute -1.5v
Out is at .41v
AFC on right (from front) is at .044v (no connection)

AM9125 board (left to right, from top)
Sepa -2.3v for both
-12v terminal is at -14v
Mut in -1.5v
Mut left 0
Mut right -11.3v
FM in -0.43v
Relay -0.8v fluctuating
+35 terminal at 30.7v

And the power supply (left to right, from underside)
0
-30v
-28.5v
-13.9v
-.06v
-.2v
 
Now it stopped working right and the am9125 relay terminal is at -30v again.

It’s basically the reverse of what it should do. On strong signals the relay turns off and on weak signals (like between stations) it turns on.
 
I also just noticed that I have two caps that are bulging that were fine before. They're on the front right-hand circuit board, the two larger 200 uf 25v caps in the back. They're in according to the polarity marked on the board, but they're definitely getting -8v to the positive terminals right now. This is a pic of someone else's receiver. I'll try messing with them in the morning and get a pic of mine then.
 
its all rather moot as i only have your schematic to look at. the 150v is DC YES? the higher voltage could be the result of your house voltage being 120vac+ and the set is designed for 115/230. if those caps are new AND bulging you had better check applied voltage and polarity.
 
This version may be a little easier to read:

PioneerSX-600TSchematic.jpg
 
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