minimood D - mod wheel disassembly ?

[soukouss]

hi there
this is my first post. i'm a 15 years professional musician, and I just bought my first Moog synth : a vintage minimoog D
it's like a dream. it sounds so good !

but i have to clean the mod wheel which is a very little bit noisy when i use it.

please can you help me with this :
I have disolder the mod wheel block, but I wonder how I can disassembly the plastic mod wheel from the pot ? Do I need to force ?
Thank you very much.
here is a picture

[thealien666]

hi there
this is my first post. i'm a 15 years professional musician, and I just bought my first Moog synth : a vintage minimoog D
it's like a dream. it sounds so good !

but i have to clean the mod wheel which is a very little bit noisy when i use it.

please can you help me with this :
I have disolder the mod wheel block, but I wonder how I can disassembly the plastic mod wheel from the pot ? Do I need to force ?
Thank you very much.

Hello and welcome.

Congrats on getting your hands on a Minimoog !

My Minimoog D mod wheels are different than yours ( ealier production run). But I imagine that there should be an Allen head set-screw at the bottom of the small round hole along the edge on top (opposite side of your photo), locking the plastic wheel to the pot shaft.

On mine, the hole with the set-screw is underneath because my wheels are complete round discs.

Hope this helps.

[muksys]

It looks similar to the wheels on my Rogue. It is simply pushed onto the pot stem. If you cannot find a hex screw holding it in, It should just come right off with a little force.

[Kevin Lightner]

The hex screw (set screw) is located deep in the hole of the C indent curve meant for your finger.
Right on the top if it was a pitch wheel at center position.
A 1/16" hex wrench is needed. CCW motion loosens.

However, with all due respect, if one cannot locate this set screw, I question how they intend on cleaning this pot.
It is normally sealed by the compression of four tabs and a resin coating.
Easier to take apart than put together tightly.
It is also a special pot and not easily replaced.
Any pot that replaces it must be a 50Kohm audio (exponential) taper AND must reach 1ohm or less when fully CCW.
This last factor is called "end resistance" and is not always included in specs for new pots.

Some people drill their pots in order to allow access for spraying a solvent or cleaner.
This might work, but can also damage a pot immediately or over time from any metal bits trapped inside.

[thealien666]

To add to what Kevin has said, when I bought my Minimoog all the knobs (potentiometers) were scratchy (electrically noisy), including the mod wheels. But after several hours of moving them from one end to the other, they all slowly started to clean themselves. And eventually, after several hours of doing that, they're all perfectly working fine now. All I had to do was to remove each mod wheel (like Soukous has already done, but without the need to go any further to remove the actual plastic wheels from the shafts) just to allow complete rotations for the cleaning moves, back and forth.

Having already seen the insides of an Allen Bradley Type J potentiometer, I had noticed that there is a carbon type contact wiper inside (instead of the usual metal one), much like an electrical motor brush, with a rather large contact surface area. And it is rubbing against the thick electrically resistive carbon trace around the base of the pot. That's probably why it tends to cleans itself after several (many many actually) complete turns, back and forth from one end to the other.

Maybe I was lucky not to have to drill a hole and shoot some contact cleaner in there, and still manage to get them to all work perfectly. But I was aware that these pots are sealed and didn't want to break that seal.

And I agree wholeheartedly with Kevin that if you can't find the hex allen setscrew on a mod wheel, maybe you shouldn't tinker with your precious (and expensive) Minimoog...

[Kevin Lightner]

Having already seen the insides of an Allen Bradley Type J potentiometer, I had noticed that there is a carbon type contact wiper inside (instead of the usual metal one), much like an electrical motor brush, with a rather large contact surface area. And it is rubbing against the thick electrically resistive carbon trace around the base of the pot. That's probably why it tends to cleans itself after several (many many actually) complete turns, back and forth from one end to the other.

True. Exercising a pot can help, but sometimes it doesn't always last.
Either way, in the case of the mod wheel pot, it should really be removed first if attempting it.
The normal shaft travel doesn't span the entire range of the pot.

When I rebuild such pots, I clean off the resistive tract and often replace the carbon wiper goody.
Some silver cement often helps.
But the resistive surface can get very glazed.
Only light abrasion (1500 grit or higher) can take it off.
Exercise can sometimes make things better, but with the original carbon wiper it can sometimes make things worse too.
It just reoccurs again.

Btw, I don't recommend abrading resistive elements unless absolutely necessary and then only on lower ohm pots.
Doing it on a 1 or 5 meg pot may ruin it.

[thealien666]

As usual, extremely useful technical info from Kevin. Thanks man!!

I just hope any of mine don't need to be rebuilt anytime soon...especially those hard to find ones. (fingers crossed).

[soukouss]

hi there
thank you all for your comments. very useful. so professional.
i finally found this allen set crew !!

i have used a 1.5mm allen key, then open the pot and clean with some air-spray & deoxydant-spray ( KF F2 )

re-build and test. all is fine now !

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since you are there, i take the opportunity to ask you 2 things :
- what is your tips to perfectly adjust a round knob onto his pot-axe, so it turns perfectly in circle ? i can't imagine moog tech not using a tool to make this adjustment fast and right for each minimoog.
- what is the way to repair some "Waveform Selector" pots. My osc1 & osc2 pots are noisy when moving position. osc3 is OK. So I suspect it could be a contact problem ( osc 1 & 2 could have been used a lot of time more than the osc 3 ) and not a "dust" problem ( the three osc selectors would be equally noisy ).

All the best for you all.