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Crunchy Tuner

Holst

Holst

Addicted Member
OK, I've run out of trouble shooting ideas. My ST-5100 has started making crunchy noises, it sounds like lightning does on AM radio, except I'm listening to FM.

It's not the antenna as I swapped my rooftop for a dipole.

It's only this tuner, my others are fine.

I sprayed the variable capacitor with non residue contact cleaner, it's still there.

It's up and down the FM dial.

It was aligned a couple years ago.

It's also my favorite tuner.
 
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Try to blow out the dust between the leaves of the air-variable cap. This is a known cause of just such crunchiness in some old-ish tuners.

On old, old, OLD tuners, this can be caused by migration of silver in the integrated silver/mica caps in the IF "cans" (transformers).

I don't know what an ST-5100 is, so I don't know if either of the above could be a bona fide possibility.
 
I shoot some air through there.

The 5100 is a Sony, the little brother of the ST-5000, built in 1970. 4 gang, 6 filter (it got a good review in High Fidelity)
 
Can you be more specific on the noise? Does it happen only when you operate the tuning knob - as in move the tuning cap? Or is this some sort of noise that's always there in the audio that's output? If so, one channel or both?

This will help those who 'armchair diagnose' things....its sort of like surgery-by-phone but with the patient having to do report the symptoms and observations. He'll get better faster with more detailed reporting.

Cheers,

David
 
It's intermittent, not touching the tuning knob. If I turn off the AFC, the signal strength and tuning meters bounce when it happens. AFC on, the meters don't move. It can be minutes or seconds between the crunch. The thunderstorm and AM radio sound analogy is the best I can think of. But it's a loud, low crunch. I thought my roof top antenna had a bad connection, but it's checked out fine. And as I said, I swapped the antenna and it's still there.
 
This is not uncommon on the Sony tuners. To correct usually you need to clean the tuning condensor shaft and the small bearings and relube under the leafs that make contact to the tuning shaft. Something better left to someone with experience as it does not take much to screw up the condensor permanentlyand usually requires removal of the dial string pulley to get at it.
 
Yeah, I'm with Brian. The tuning cap will need some serious cleaning of contacts to eliminate it from the list of possibilities. I always assume mechanical problems before electronic ones so this is a good starting point.

I'm not clear that the dial string needs to be taken apart but knowing where to clean is far better than a general 'shotgun' approach to spraying everything in sight.

Isn't there a sticky or other online references on how to clean tuning caps? Yep, here's one from the archives: http://www.audiokarma.org/forums/archive/index.php/t-45404.html. Check Dr*Audio's suggestions.

Cheers,

David
 
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