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I posted about this problem last week. Someone responded to pull off the face and spray the volume control with WD 40. You have to unscrew the circuit board first . It works.
I'd be cautious about that. There are sprays made for cleaning volume control potentiometers, but WD40 isn't one of them. Check out Radio Shack for stuff like this.

Also, I'm pretty sure that my double DIN Monsoon system does NOT use a typical potentiometer volume control. Instead it uses some kind of encoder, maybe optical. I know this for two reasons: 1) there is no stop on the control (I can turn it either way forever and never encounter a stop), and 2) it has indents as it is turned. I've watched it carefully and the volume is controlled in small steps, rather than continuously.

Because the volume level is controlled by an encoder, some sort of microprocessor is used to handle the encoder output and convert this to a volume level. That, in turn, means that there's something about that microprocessor that prevents the volume from going low enough. Fix the uP and you fix the problem. That fix may be as simple as a master reset, however that may be accomplished. Of course, it also could be a problem someplace else.

Note that the tone, balance, and fader controls are analog potentiometers. I'm sure that was done because those controls don't get the use that a volume control does. Because of the way potentiometers are made they will eventually wear out, but an optical encoder won't.
 

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Note that the tone, balance, and fader controls are analog potentiometers. I'm sure that was done because those controls don't get the use that a volume control does. Because of the way potentiometers are made they will eventually wear out, but an optical encoder won't.
"Logic" control also makes it easier to include features like steering wheel volume controls.
 

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"Logic" control also makes it easier to include features like steering wheel volume controls.
Yep, it sure does.

Alas, we haven't gotten any closer to the OP's original problem: the min level of his volume control isn't what it's supposed to be. It could be a failure in the radio's logic circuits. Perhaps some bits are "stuck" on (shoted transistor/diode switches) and an IC needs to be replaced. But it would be nice if we could figure out how to do a Master Reset on the radio to get it back to a new-out-of-the-box state.
 

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I just double checked and realized I posted on the Bentley Publishers website. My volume control seemed to be out of control - if I turned it to the left a couple clicks it would slightly reduce the volume but the next click to the left would suddenly increase the volume, blowing my eardrums. I never knew where it would be the next time I turned it on. I have a 99 with the factory single din radio/tape/cd changer. Here is the response I got from Turbo510:
"The problem is almost certainly the volume control encoder. I had the same issue with my wife's 1999 last year. The contacts in the encoder become contaminated or corroded, so the sound system's microcontroller doesn't get the command to turn down the volume, or turns it up instead of down, which is often what her's did.

I removed the face of the sound system, which has the display and controls. I wish that I had taken pictures along the way, but by inspection you can see what to unscrew to get the potentiometer exposed. It can't really be taken apart, but there are tiny openings that I blasted some WD-40 into. It's not 100% restored, but close enough that the volume never blasts."
 

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Aha! So it may not be an optical encoder. In that case, contact cleaner may be the best option. Again, WD40 isn't particularly good contact cleaner. Use the Real Thing: Cleaner and Lubricant, Radio Shack stock number 640-4315.
 
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