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 Post subject: TO Royal-7000: crackling in the AM-SW bands.
PostPosted: Feb Sat 24, 2018 4:10 pm 
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Joined: Feb Fri 26, 2016 3:08 am
Posts: 23
Location: Richmond, KY
A TO Royal 7000 (Chassis 18zt40z3) followed me home. RF performance appears ok. The single Weather channel works, and so does the FM band (from bottom to top). I gave the transistors and the switches a quick cleaning (de-Oxit and pull in and out of the sockets for the transistors) and the FM sounds pretty good.

The problem: in MW (and shortwave too) there seems to be a point, turning the tuning knob, in which something is loosing contact (or makes contact where it is not supposed too) and the band goes dead, with lots of crackling sounds.

Jiggling (shaking, bumping, whatever you want to call it) can make a station come in in the "dead zone" and, at time, it sounds full as it should but it is temporary.

I observed similar behavior long time ago in a TO H500 that, to tune and sound, had to have the tuning capacitor "propped up" with a thick piece of paper.

In the TO Royal-7000 the tuning capacitor is held in place by three screws and three rubber grommets. The rubber is of course now hard as a rock. I think the culprit is there.
Any easy replacements in existence?

Any other suggestions? Barking up the wrong tree?
Thanks!
Marco


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 Post subject: Re: TO Royal-7000: crackling in the AM-SW bands.
PostPosted: Feb Mon 26, 2018 1:54 am 
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Joined: Jan Sun 06, 2008 3:28 am
Posts: 4055
Location: Richmond, VA
Cracking or popping sounds that occur in the same spot while tuning could be shorted rotors and stators, or conductive grit in the tuning capacitor.

I haven't done a Royal 7000, but I've used rubber grommets available at hardware stores to renew the grommets on vintage radios, sometimes you get lucky and can do it without disconnecting leads to the tuning cap.

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Ed


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 Post subject: Re: TO Royal-7000: crackling in the AM-SW bands.
PostPosted: Feb Mon 26, 2018 4:52 pm 
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Joined: Feb Fri 26, 2016 3:08 am
Posts: 23
Location: Richmond, KY
Hello Ed:
The rotor and stator touching in the tuning capacitor was the first thing I thought but why does not do it in in the FM band? Unless I don't understand how the fm band is tuned, which is entirely possible. In any case, it looks that a trip to Ace hardware is in order, as those grommet are hard as a rock.
Marco


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 Post subject: Re: TO Royal-7000: crackling in the AM-SW bands.
PostPosted: Mar Sun 04, 2018 4:11 pm 
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Location: San Diego, CA
Phyciocc wrote:
Hello Ed:
The rotor and stator touching in the tuning capacitor was the first thing I thought but why does not do it in in the FM band? Unless I don't understand how the fm band is tuned, which is entirely possible.
Marco


The AM, SW and FM bands all use different sets of plates on the variable capacitor. If you look at it you will see different sections.
Rick


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 Post subject: Re: TO Royal-7000: crackling in the AM-SW bands.
PostPosted: Mar Mon 05, 2018 1:09 am 
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Joined: Aug Wed 24, 2011 4:35 am
Posts: 4091
Location: Sunnyvale CA
gridleakrick wrote:
Phyciocc wrote:
Hello Ed:
The rotor and stator touching in the tuning capacitor was the first thing I thought but why does not do it in in the FM band? Unless I don't understand how the fm band is tuned, which is entirely possible.
Marco


The AM, SW and FM bands all use different sets of plates on the variable capacitor. If you look at it you will see different sections.
Rick


The FM is not tuned using the capaictor. FM uses slug tuning driven by a worm gear. AM and SW use the same capacitor plates. The three different plate sections are the oscillator, mixer, and antenna tuning sections for all AM bands (BC and SW).

I think the previous responses cover the potential problems pretty well. But it's very unusual for these plates to short out, because you really have to try to get in there and bend the fins. Conductive debris is certainly possible, but my money would be on corrosion on the "fingers" that make the electrical connection between the rotor and the chassis. Working it back and forth a bunch of times, and you might burnish the finger and remove the corrosion.

Brett


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