Twitchy Tuner

[LBPete]

I've just finished recapping a Sansui 7070 receiver. The tuner has developed an odd issue. At the lower end of the dial, it has trouble "locking on" a station. If you turn the dial slowly across a station, the signal strength and tuning meters jump around and the muting and FM stereo light kick in and out. You have to kind of "fish around" to find the station and when you take your hand off the dial, you may loose it. You can dial in stronger stations with a little screwing around but not weaker ones. Once you get up around 95 or 96 it seems to work normally from there to the top of the dial.

I've checked the cap installations on the tuner boards and the polarity is all correct and the solder joints look good. I've also cleaned the ground contact in the tuning cap. To eliminate that, I connected a jumper from the shaft to the chassis. It had no real affect.

Have the new caps awakened an old problem? Is it alignment time? Any other suggestions?

- Pete

[Fred Longworth]

The ganged tuner has moving contacts on which the rotor assembly rotates in the stator frame. Some of the moving contacts use ball-bearings, others use spring plates. Either way, these moving contacts oxidize and pick up contaminants, and when they do the tuner becomes very touchy. Lubricate these with small amounts of Teflon lube or DeoxIT, and then run the rotor up and down the dial all the way about twenty times. This should fix your problem.

Fred

[LBPete]

Fred, that's what it acts like. Something is not making good contact. I've cleaned the spring clip with contact cleaner and lubed it with a couple of drops of 100% deoxit. I've also grounded the shaft with a jumper. It doesn't change anything. Here's a picture of the spring clip and jumper.

I would think if it's loosing the ground through the clip, the problem would go away when the jumper was in place.

- Pete

[LBPete]

By George, I think I've got it. Definitely a cleaning issue. It was really bad today. It wouldn't tune a station with the mute on. The jumper wire had no affect so that is not a valid test.

I went through another cleaning cycle and it improved but it still wasn't right. If I shook the tuning wheel everything would start jumping. I noticed there are also contact clips between the gangs where the shaft passes through the frame. I cleaned them and applied a little 100% deoxit and presto, it worked. It tunes normally now and pulls in weak stations. I was listening to 91X the Tijuana punk rock station. Came in loud and clear, over 125 miles away.

The center tuning is a little off on weak stations. Some tuners have a trimmer pot to adjust it but this one needs to have a coil tweaked. I tried turning it with a plastic screw driver but it wouldn't budge. I'm afraid to force it. It might snap loose and turn too far. Is there are technique to free them up?

- Pete