Tuning knob: slightly stiff when turned. How to fix?

[monkboughtlunch]

My Fisher 400 has a very smooth fluid feel when the FM tuning knob is turned. In contrast, my 800B's separate AM and FM tuning sections feel a little gummy when turned. The FM on the 800B has a little more resistance than the AM when turned.

I'm guessing this is a lubrication or dried grease issue with the separate tuning mechanisms. There are a series of pulleys as well as the turning capacitors.

Is this a common issue and what is the best approach return the tuning mechanisms to the original smooth and fluid feel? Where is the most likely location of the resistance?

 

[gadget73]

usually I put a drop of light oil on all of the moving parts. Use a needle oiler to make sure the oil doesn't get all over, but one drop in the tuning condensor at each end of the shaft, one on the tuning knob shaft where it passes through it's mounts, and one on each pulley gets it done pretty nicely. Be very careful around the tuning condensor, you don't want to bend the fins or get oil all over the place. Originally they had a bit of grease in the pulley end, but it petrifies after a half century or so.

 

[larryderouin]

If you should get oil on the tuning fins, and even if you don't, a cleaning of the tuning cap is a good idea after 50+ years. Go down to Home Depot and get a can of CRC QD Electronics Cleaner. It's a NON RESIDUE cleaner. This is very important with regard to the tuning capacitor. It's what's called an air gap capacitor, and anything (dust, dirt, oil residues, finger oils residue, etc., WILL change it's capacitance and therefore the tuning will be screwed up. Turn the tuner so the movable fins are outside of the fixed fins. Tilt the unit on it's side with the tuning cap on the lower side. Spray liberally all fins and both sides of all fins. Don't worry about surrounding surfaces, components, etc., from overspray. It won't hurt them AND it will evaporate in less than a couple of minutes. Wait 20 minutes and crank it up and check the tuning. If it's all mucked up, turn off the unit and let it dry more. 12-24 hours should do it. But in my experience with cleaning caps this way, I've been able to crank them up and have tuning within 30 minutes.

 

[rufleruf]

I had a 400 with a nearly impossible to turn tuning condensor - took a lot of effort to get it free and working. I have a rosin bottle with penetrating oil for just this operation. Some heat helps too.

 

[larryderouin]

PB Blaster, or Liquid Wrench in a needle applicator are best used for this application. With a stiff tuning knob, take off the knob, flip up the unit on it's back, so the unit's controls are on top facing UP! Remove the front panel to access the outer housing for the knob shaft. Drizzle a few drops on the knob shaft and let it flow down into the space between the knob shaft and the bushing housing. With another needle applicator filled with sewing machine oil (never use 3 in 1 oil in the RED BOTTLE). Too much wax and it will gum up the works. If you DO use 3 in1, use the BLUE BOTTLE ONLY. It's a non detergent 20w motor oil and is a little heavier than sewing machine oil. I prefer sewing Machine oil 1st and 3 in 1 2nd for this. But if sewing machine oil not avail, go ahead and use the 3in1 BLUE BOTTLE).

Back on track. Let the Penetrant sit for 24 hours in the knob bushing. Occasionally give it a 1/4 to 1/2 turn in opposite directions each time. This will help get the crud loosened up. For the pulleys one small drop of oil underneath the pulley against the shaft. Do all of them then turn the knob a couple turns both ways.

Be extremely careful when doing the bearings on the ends of the tuning capacitor.(See 1st para.) As a precaution, DO use the CRC on the fins AFTER oiling the bearings on the tuning cap.

 

[gadget73]

I'm not super picky with my oils, but it usually ends up being sewing machine oil since thats what I have nearby the bench. Failing that I usually go for hydraulic oil or lathe spindle oil. I'm not sure its overly critical for this, its an extremely low speed bearing and you just want to get something slippery in there. Some penetrating oils don't stick around long term though.

 

[rufleruf]

If Avery had known we'd be fussing over these things almost 60 years later he would have provided zerk fittings

 

[gadget73]

probably would have made it worse honestly. Over-lubrication ruins things just like lack of lube does. Grease also oxidizes and turns hard, which is the issue we have now. I work with radiation, grease fails way faster but its overall a similar effect. What I see at work in a year's time is what the rest of the world sees in 50. Adding more grease really doesn't reverse it, and often the extra grease just ends up turning into a larger solid mass.

 

[larryderouin]

Gadget's next movie is going to be a real squeaker. The attack of the 50year old grease blobs. In Technicolor and Vista-Vision to get all of them in one shot of that horrific beige gray!!!

 

[gadget73]

unfortunately you'd need smell-o-vision to get the full effect. There is a very unwholesome smell to heavily irradiated grease.