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Old 14th November 2006, 08:31 AM   #1
Stuey is offline Stuey  Australia
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Default How does this volume control work?

Hi all,

I've promised my old Mum that I'll have a look at her Sony all in one CD/MD/Tuner unit. It has an issue with the volume control that I'm not too sure about.

The control turns infinitely (it's meant to) and the output level is displayed graphically on an LCD from 0 to 35 units. The problem is that the level increase/decrease stalls at various points of the scale and sometimes won't move at all unless you turn it very slowly and carefully. Even then it's not guaranteed.

My question is - how does this unit work? As I say, you can keep turning it - it has no stops - and the scale currently takes about 40 turns to get to 'full volume'. I'm guessing the control 'pot' needs replacement, but what is it, exactly?

Any help would be greatly appreciated.

Cheers

Stuey
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Old 14th November 2006, 08:50 AM   #2
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It's a rotary encoder. There are lots of different types, so you really have to pop the lid and see if it has any ID on it or post some pics if you want a replacement. However, a bit of contact cleaner may well sort it out.
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Old 14th November 2006, 09:13 AM   #3
Duo is offline Duo  Canada
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Yeah when those get dirty they can be very touchy.

It often has just a series of contacts set up to output grey code or binary as you turn the dial.
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Old 14th November 2006, 10:08 AM   #4
Stuey is offline Stuey  Australia
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Thank you guys. I actually thought of a rotary encoder after seeing them in an electronics catalogue (Altronics here in Australia) but wasn't sure what these really were! I might have to search out some info as I'm interested in their construction.

I've 'popped the lid' but it's well hidden behind some PCB's. I'll properly unearth the unit and try some contact cleaner.

Thanks again!

Stuey
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Old 15th November 2006, 09:01 AM   #5
Stuey is offline Stuey  Australia
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Just to complete the story, I removed the offending PCB containing the encoder, and it was a matter of seconds' work to bend back the tabs on the encoder and pull the casing apart.

The problem was merely an excess of grease, which I removed almost completely with some lighter fluid. I left a smattering behind, though.

It now works perfectly.

Thanks again.

Stuey
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Old 15th November 2006, 09:47 AM   #6
AndrewT is offline AndrewT  Scotland
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Hi,
the rotary encoder may be solid state (no contacts) and could be optical or hall effect or some other SS mechanism.
It simply has to send pulse data to the electronic volume control for the scale and volume to change.
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Old 15th November 2006, 10:29 AM   #7
Duo is offline Duo  Canada
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I have found in some of those that the grease manages to collect a buildup of either worn off contact material, or just grime from its surroundings. This can really gum things up.

Good work Stuey.
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Old 15th November 2006, 01:11 PM   #8
Stuey is offline Stuey  Australia
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Cheers.

Andrew, it had three wipers similar to those in a potentiometer, bearing on two tracks of differently spaced alternating metal/insulator 'spokes'.

I guessed that the wipers were floating on the grease and not receiving the required pulse to provide the step increase in volume.

Stu
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