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Old 9th Sep 2019, 11:19 am   #1
grundig1
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Default Variable capacitor blocked

Hi.
I have Grundig C4200
It was not possible to change radio stations (round wheel rotating without effect), so I have dismantled the radio and saw that the variable capacitor is totally blocked. Turning the white sprocket wheel or trying to move the rotor is not possible.
Any suggestions why this happened and how to repair it?
Regards,
Grundig1
Location: Slovenia
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Old 9th Sep 2019, 12:20 pm   #2
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Default Re: Variable capacitor blocked

Something has jammed somewhere. Don't try to force things or you'll strip the teeth off the plastic gears.

There's bound to be some backlash in the system, so by gently rotating the tuning knob or tuning capacitor whilst observing closely you should be able to see what's jammed.

Failing that you'll have to dismantle the drive. It may be possible to unlock the shaft coupler by slackening the grub screws.
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Old 9th Sep 2019, 1:04 pm   #3
grundig1
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Default Re: Variable capacitor blocked

Tuning capacitor, tuning knob, everything is blocked.
I think I will have to dismantle it. I can't see any screws, on one side of the shaft there is something similar to a screw, but its hole is too shallow to put a screwdriver in.

Is putting the whole variable capacitor out too hard for a layman? I'm guessing there is unsoldering on the back of the plate needed?
I will be back home on Friday, so I am currently only collecting advices.
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Old 9th Sep 2019, 1:30 pm   #4
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Default Re: Variable capacitor blocked

Quote:
Originally Posted by grundig1 View Post
on one side of the shaft there is something similar to a screw, but its hole is too shallow to put a screwdriver in.
That's the grub screw I referred to. A suitable tool should fit it. Could the hole be a hexagon for a Hex Key?

You'd do better dismantling the gear train rather than trying to remove the tuning capacitor.
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Old 9th Sep 2019, 10:35 pm   #5
Goldieoldie
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Default Re: Variable capacitor blocked

Hi
It could be the grease in the metal coupler / capacitor shaft has gone hard .
Try putting a soldering iron on it and if you can get some penetrating oil in there
Be careful the plastic cog does not get too hot !
Cheers
Pete
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Old 9th Sep 2019, 10:48 pm   #6
60 oldjohn
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Default Re: Variable capacitor blocked

It is very common for these to seize or block, the grease goes hard. You need heat as already said, not easy without damaging other parts. The grease needs to come out and get some thin oil in. If the old grease is left in you will have same trouble soon.


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Old 10th Sep 2019, 9:22 am   #7
crackle
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Default Re: Variable capacitor blocked

Grundig transistor radios are well known for this, it is a failing to what otherwise are always nice radios.
It also happens to a few other radios which use a similar cast metal frame for the tuning capacitor.
Yes heat from a 30 watt soldering iron tip, to soften the hardened grease, then it needs to be worked and worked back and forth with penetrating oil to try and flush out the old grease. Then when totally free put some drops of thin sewing machine oil on the shaft.
If you can remove any plastic gears or wheels then so much the better because a lot of heat is sometimes needed to melt the hard grease, and the plastic can also melt.

Mike
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Old 10th Sep 2019, 10:50 am   #8
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Default Re: Variable capacitor blocked

Very common. The grease sets like glue after many years. I would suggest you remove the gears if it's easy enough to do because even if you don't use heat, some oils can attack plastic end then if the gears crack, you really will be in trouble......
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Old 22nd Sep 2019, 10:52 pm   #9
grundig1
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Default Re: Variable capacitor blocked

Thank you, I heated the shaft and changing stations now works perfectly.

But after some days another problem appeared. Suddenly the bass disappears, so the sound is completely without bass (low frequencies). If I press the volume slider, bass often comes back and the sound is normal, but not for long.
Before dismantling again, any suggestions?
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Old 25th Sep 2019, 2:51 pm   #10
grundig1
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Default Re: Variable capacitor blocked

Ok I have cleaned the potentiometer with isopropanole and it is a lot better now. So this radio is considered repaired now and is in use everyday.
G.
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