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 Post subject: FADA 652 Tuning Problem - SOLVED
PostPosted: Oct Thu 14, 2021 2:51 am 
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Joined: Jun Mon 01, 2015 9:34 pm
Posts: 1551
Location: Greenville, TX
I am working on a 652 which only tunes the upper half of the BC band. It makes a scratching noise at mid-band but I cannot see any touching tuner plates.

http://www.nostalgiaair.org/pagesbymode ... 005658.pdf

Thank you,

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http://www.dalesantiqueradio.com/


Last edited by radiodale1 on Oct Sat 16, 2021 5:51 pm, edited 1 time in total.

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 Post subject: Re: FADA 652 Tuning Problem
PostPosted: Oct Thu 14, 2021 3:27 am 
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Joined: Feb Sat 06, 2016 1:47 am
Posts: 3620
Location: La Mesa Califonia
Blow out tuner gangs with compressed air. Clean copper contacts on moving gang to frame. Normally it's the end gangs that get bent a little. Try spreading them just a touch.


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 Post subject: Re: FADA 652 Tuning Problem
PostPosted: Oct Thu 14, 2021 4:11 am 
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Joined: Jun Mon 01, 2015 9:34 pm
Posts: 1551
Location: Greenville, TX
Thank you, looks like others have also used cap checkers to flash small metal pieces. I will try both.

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 Post subject: Re: FADA 652 Tuning Problem
PostPosted: Oct Thu 14, 2021 5:10 am 
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Joined: Feb Sun 01, 2009 2:56 pm
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Location: Victoria, Australia
If you can manage to keep the stuff out of everything else, the best grot remover is a foaming automotive Aluminium wheel cleaner. Correct; Its commonly the outer vanes of the rotor that get bent and short. Check first but isolate the gangs (un-wire) when using an ohmmeter

Often a piece of card paper, perhaps Emery Paper will help cleaning between the vanes; If that is the problem.

I have no qualms with the Insulation tester method, if it has corrosive mounds. This is a method where you can zap yourself: Beware: one does not use transfomers, or utility power, like some oldies did. I use 500-1000V. if it does not flashover at 500V all is well. This will also show which vane is bent, or the issue, in dim light and burn off the corrosive mounds.

Marcc


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 Post subject: Re: FADA 652 Tuning Problem
PostPosted: Oct Thu 14, 2021 6:23 pm 
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Joined: Jan Mon 16, 2012 4:15 pm
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Location: Near Brandon, Iowa
If you decide to try the "high voitage zapper" approach, first ensure that the tuning cap has been disconnected from the radio. Otherwise you will destroy the antenna transformer.


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 Post subject: Re: FADA 652 Tuning Problem
PostPosted: Oct Fri 15, 2021 12:05 am 
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Location: Victoria, Australia
lorenz200w wrote:
If you decide to try the "high voitage zapper" approach, first ensure that the tuning cap has been disconnected from the radio. Otherwise you will destroy the antenna transformer.


+1. This is the method of last resort, where every other is going to cause damage, or prove ineffective. If you do not isolate the gang the insulation tester is never going to get past zero volts. Use short bursts, that apparatus was not designed to be a power supply.

It goes without saying that 500-1000VDC is not friendly. Therefore all precautions to avoid getting you fingers in contact with it apply. This process is more interesting and effective in its application in dim light.

Marcc


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 Post subject: Re: FADA 652 Tuning Problem - SOLVED
PostPosted: Oct Sat 16, 2021 5:57 pm 
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Joined: Jun Mon 01, 2015 9:34 pm
Posts: 1551
Location: Greenville, TX
Cap checker didn't work so I removed the tuner (and the dial cord!). Couldn't see anything so I connected my ohmmeter and observed it while I messed with the outer plates. Suddenly the short was gone. Waited for a few minutes to see if it would return, and reassembled. Thx for the ideas.

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http://www.dalesantiqueradio.com/


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 Post subject: Re: FADA 652 Tuning Problem - SOLVED
PostPosted: Oct Sat 16, 2021 11:42 pm 
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Joined: Feb Sun 01, 2009 2:56 pm
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Location: Victoria, Australia
One of the last things I do before powering, is go over every soldered joint and mark it after inspecting it, irrespective of who did it. I have found a few factory oversights that way.

The other thing in doing that, is to ensure there is no fouling (albeit you should have spotted that already), incorporting houskeeping. That means that you ensure that there is no debris like solder & bits of wire inside the chassis and tuning gang, that can come loose & short something.

Marcc


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