Pioneer TX-9500II AM troubleshooting question

[thxdave]

Have a wonderful Pioneer 9500II that has been an amazing tuner with the best FM selectivity I've ever had. I moved a few months ago and finally set it up again in a new place where I cannot put up an outdoor antenna <sigh> so the FM struggles to give me good reception. However, the AM has gone almost completely dead.

I verified that the FM was doing everything right and it's dead-on accurate and sounds wonderful. However, the AM is all but silent....NO background hiss or static across the dial. If I tune across the band past known stations, I might get a "pip" of sound before it goes back to complete silence. I have occasionally been able to get a station to become audible if I rock the tuner back and forth across the "pip" and it will be listenable until I tune away to the next station.

Is there any good place to start checking to diagnose this behavior? Controls all seem quiet, too.

Dave

 

[Bully82]

I'm going to key on your description of rocking back and forth causing it to start working. It may be that the contacts in the variable tuning capacitor need to be cleaned. The tuning cap is composed of vanes that mesh more or less together to adjust the capacitance. The main shaft has several spots where it passes thru the metal housing, and each of these spots has some kind of bearing material that makes electrical connection between the shaft and the housing. If there is oxidation or corrosion in there, it causes unstable tuning. You can apply one or two drops of De-Oxit to each spot, using a Q-tip or toothpick. Follow by spinning the dial all the way up and down the dial a few times. Don't use a spray, and don't get De-Oxit or any other cleaner on the capacitor vanes. Residue on the vanes can throw off the front end alignment. This should fix or greatly improve the tuning, assuming this is the problem. You might have to repeat if it is really bad.

Don

 

[thxdave]

GMTA, Don. I failed to mention in my original post that your solution was the very first thing I tried. I have the little De-Oxit bottles with the needle applicator and applied a tiny amount at each of the brass/steel contact points. This has helped me bring several tuners back to life in the past but not this time. I'm open to where to look next.

Dave

 

[gadget73]

see if you have a cracked solder joint on one of the wires going into the tuning condenser. Had an old Sherwood that was dead on FM in a similar way. Found a coil that sat between the condenser and ground broken loose at one end, and moving it just the right way would get it to make contact again.

 

[DEAFASABAT]

Could also be one or more of the conductors of the am antenna that folds out from the rear panel. I'm sure that one (at least) of the coils on it is part of the local oscillator/mixer circuits, an open could definitely make it "go dead".
I have the same tuner. I'll dig around for the service manual, it might be helpful.