View Full Version : Deoxit for electronic tuner knobs?

11-23-2016, 11:20 PM
On my Avante there are a few of the tuner knobs (actually a rolling wheel) that are pretty touchy when trying to tune in a channel. They are also a bit unstable once I think I got it right. I was wondering how these wheels work and if they require cleaning like pots.

11-23-2016, 11:27 PM
One other thing. The instructions state to remove the thumb wheel cover. Mine are exposed already, so am I missing the cover for them?

11-24-2016, 12:38 AM
I've never had good luck with any varactor tuner. I much prefer knobs with actual fine tuning wheels. I tried tuning channel 16 on a varactor tuned VCR once, and I couldn't even find the channel at all.

Electronic M
11-24-2016, 12:41 AM
Yes you likely are missing the thumb wheel cover. I have a similar Avante only no picture adjustments next to the thumb wheels, and there is an inner cover under the door hiding the wheels.

Those thumb wheels ARE almost certainly pots.....You see in varactor tuners the variable tuned element is a varactor diode....A diode that changes it's junction capacitance in proportion to the (IIRC)current flowing through it....So basically they use a resistor bias network to set the tuning of the varactor diode....That resistor can be a single pot (in the case of cheap SS single knob continuously tuned portables), or it can be a group of pots that are swapped for one-another with a switch scheme such as in your Zenith and many other varactor tuned sets of that time.

The advantage of your Zenith is that you could set up a good number of exactly tuned presets in any order you desire...The drawback is that you have a bunch of pots and a big switch to clean.

As digital logic cheapened they replaced the pots with digital gating of varactor current and made fully electronic tuners....They were also able to integrate auto-fine tuning and the like easier.

11-24-2016, 09:07 AM
Yup they are pots. We used WD40 but it was rare one
got so noisy. That assy was a bear to work with so
dont tear it down unless a last resort. In the olden
days you could buy it exchange. Since they always had
a new triac & isolator that was half the cost plus the
labor saved dealing with it. The cover is just a cover....

73 Zeno:smoke:

11-24-2016, 11:32 AM
It's been a few years, but I believe the red pointers are connected to slider pots. They did tend to get dirty like any pot. You can try deoxit, but you might have to disassemble it to get it really clean.

11-26-2016, 09:32 AM
The Heathkit GR2000 and 2001 used pots like these for the presets. Be careful if you spray it with a cleaner. Some cleaners will cause the plastic to melt.

11-28-2016, 04:59 PM
I think I'll just go with the ones that tune correctly. Don't want to make things worse or create a whole new issue. I really only need two of them tuned properly.

If anyone has a pic of the tuner wheel cover, please post it. If anyone knows where I can find one, I would appreciate it.


Electronic M
11-28-2016, 05:14 PM
If anyone has a pic of the tuner wheel cover, please post it.

Behold! ( ( (

Jon A.
11-28-2016, 05:25 PM
Who'd a' thunk it? Zenith pulled out all the stops with this model.

Electronic M
11-28-2016, 05:31 PM
Ohh yes! If I were told I could only have one CCII Zenith I'd cling to my Avanti pictured above... Probably the best SS set I've owned, and ever will own.

Jon A.
11-28-2016, 08:38 PM
25EC58 eh? Chassis mounted on plywood? Saw one with plywood under the chassis in a focus troubleshooting video. My 25DC56 Chromacolor chassis is sitting on particle board, the top is particle board and the rest of the cabinet is a plastic probably inferior to that of yours. The only solid wood is screwed into the base to hold the casters. Well, at least the CRT tested new. Eventually I'll address the horizontal sync issue and overhaul the fussy SC500 drive system.

Electronic M
11-28-2016, 09:28 PM
Nope mine is a 25DC56 too.

I don't mind particle much unless it is coming apart...The Chip board Zenith used in the 60's actually bugs me more...

They are great sets once working. Mine had a weird issue of half the screen being monochrome on one half...A lytic under the chroma module died. Replacing that got it back to 100%.

12-01-2016, 06:34 PM
Interesting. Seems your thumb wheel cover is larger than what would fit mine. Guess that's because your wheels are on both sides. If I look at mine, and how a cover would fit, it would only fit over the wheels. There seems to be a small indentation top and bottom for the cover and that cover would only be about an inch or so wide. This would leave the pointer widows exposed, but I'm sure they are just wanting to protect the wheels from accidental rotation and dust.

Thanks for the pic. I'm sure if I am patient I will find one.