Minimoog Model D keyboard issues

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1

Hi there

Finally i have a reason to post here! :sunglasses:

I just get one of my dream synths, a Model D!
It is really clean inside, actually i can’t believe his state when i disassemble the keyboard (specially compared with my Odyssey, that also needed j-wire tweaking).

I bought this mini as “broken”, but after a few tests i come to the conclusion that only the keyboard and one or two noisy pots, needs attention.
So, i toke off the keyboard and gently cleaned the buss bar. After i tried to gently bend the springs so the pitch contact occur before the trigger contact, (tricky job #1).
Before assembling it again, the keyboard was tracking very good, almost perfect, but when i put the keyboard in it’s place (tricky job #2), it started to act on me again, and this time i only get pitch in the lower octave, then it’s constant pitch.

If someone can give me some tips to try to fix the keyboard, and maybe how to clean the pots, i will be extremely grateful.

Cheers

2

Hello hmvinyl, and welcome !

Your story sounds like mine a little, when I finally found my Mini.

Some scratchy pots, misfiring notes, siren wailing sounds, impossible to tune to A440 with the master tune knob, and a few other minor things.

The scratchy pots fixed themselves after about 100 complete movements from one end to the other. Most of these are sealed type, with a carbon wiper instead of the regular metal one. Looks like an electric motor brush, and after rubbing several times on the plastic resistive surface, it cleans it of oxidation traces. Anyway, it did on mine…

The misfiring and wailing sound was, of course, caused by dirty, oxidized buss bars and coil springs in the electrical part of the keyboard. So I did like you, took the keyboard out, painstakingly cleaned with alcohol and realigned the buss bars and springs. Not contact cleaner. Isopropyl alcohol. Why ? Because after a while, the residue left by contact cleaners like Deoxit will cause trouble again after only a few weeks.

I had managed to get a reasonably well working keyboard. But when I put it back inside the synth, all hell broke loose ! The pitch was all over the place, although each note was firing (triggering) properly. What did I do wrong ? Nothing really. The dreaded Cinch Jones bakelite keyboard connector was looking okay but was actually oxidized too ! Not only that but the one from the Mod wheel assembly as well !

That was the source of the tuning problem. On top of that, the pitch bend wheel had been offset on the potentiometer shaft !!

After thoroughly cleaning all the contact pins of those Cinch Jones connector, and realigning the plastic pitch bend wheel to center position, I could now get close to A440 when tuning with the master tune knob.
I still needed to calibrate the oscillators individually for better tracking.

Even though I had cleaned to buss bars and springs with alcohol, after about 6-8 months, the keyboard started to act up again. Darn ! I really didn’t want to clean it again… So I found Kevin Lightner’s OptoKey system to replace all the electromechanical contacts with optical ones, ordered it and installed it.

So, I hope my little story might help you go through the early moments of owning a Mini in need of some TLC…
BTW, I can’t tell you how many times Kevin has helped me out, directly or through this forum while helping others, with very valuable info on fixing and maintaining my beloved Minimoog D !

Hope everything turns out great for ya !
Alain.

3

Hi Alain, thanks for sharing your story.
I am thinking on the optokey for mine, but i need to hold a bit to raise some more funds.

I can’t find anywhere in my country isopropyl alcohol, so i use contact spray.. I know it was not the best option - will a regular alcohol be ok for the job?
I will try to clean also the cinch jones connector and see if that helps.

Any special trick to have the pitch spring doing contact before the trigger spring?

4

Of course, regular alcohol will do. It should be an about 95 %er, and not 75 % as there’s too much water inside. And water contains oxygen. When you put metal parts in a 75%er (I think isopropyl is this one) they’re going to get rusty if you leave them inside for one night.
But when you’ll go also in a special store for electronic parts you’ll going to have a huge choice of cleaner sprays. To start from “very acrid” for plugs and contacts up to “low acrid” i.ex. for PCBs. The guys who work there will advise you pretty well.

As for the contact springs there are different holes in the plastic band. So get them out carefully and put them into a more suitable. But changing into another hole might worsen the issue or stress the springs to much. Check it out first by viewing if other holes may improve action.

5

I have here a pcb spray cleaner, is it ok for cleaning the buss bar / springs?

6

I didn’t tried to pull off the contact springs, because i thought it will be a nightmare to put them back again..

7

For info, most drugstores sell 99% pure isopropyl alcohol (also sometimes called isopropanol). That’s what I use to clean contacts. But you might have to ask for it.

8

I managed to get 96% alcohol, thanks for the advice.

But… i think i screwed must of the springs for good, one of them is actually broken :cry:
Man, this keyboard system is the supreme pain in the a**

So basically i have a fully working model d with no keyboard :unamused:

*FYI i have no experienced technicians near me.

9

Actually 99% pure isopropyl is not easy to find, at least in the US, outside of the internet. I have to go to an old school electronics store to get mine.

10

Here in canada you have to ask for it, as it it not freely available on shelves. It is a very flammable and poisonous product to be handled carefully (avoiding breathing vapors, and avoiding contact with skin or eyes or heat source is critical).

But since he managed to find 96% pure, it’s a pretty good percentage to clean things… Unfortunately, one of his springs broke. It happened to me too, but I had managed to solder it back together (it broke at the base, so I was lucky). My repair didn’t look very good, but it worked. Soon after I went and e-mailed Kevin about his product… :mrgreen:

Here’s a close-up shot of my soldered spring (don’t mind the dust, the contacts have been in storage for a long while now):

11

Honestly, i stupid i was..
The springs were ok, they were not making the contact at the right order though, so ended up messing most of them :frowning:

Just for your entertainment:

:blush:

12

Ouch…

13

My 2 cents…

  1. Tarn-X chemical detarnishing can really help.
    Available in the states at most drug stores.
    (Always remember to rinse the stuff off completely.)

  2. It is possible to polish buss bars with fine polish such as 3M 39527 chrome polish.
    One can carefully remove a buss bar (always pull, never push) or apply with swaps and buff shiny.

  3. Buss bars can often be helped by simply rotating them a 1/4 turn or whatever.
    Desolder the end and use pliers on an unused area.
    This instantly changes the point of contact from one that’s seen 30-40 years of friction to one that’s seen none.

  4. The last batch of OptoKeys is basically finished except for some minor details.
    That means there’s only 3-4 left.
    The entire design of this product is for sale however.
    Someone else might begin making them again later.
    But for now, they’re very quickly running out here.

Good luck with your Mini! :slight_smile:

Kevin “Synthfool” Lightner

14

For cleaning it’s always the best to take the most soft liquid as said above. Just “simple” alcohol, high percented is o.k.
I’m using a completely disappearing none acridly spray and it’s working fine so far. But despite I try avoiding contact with PCBs as possible.

As for the keys as I remember the plastic parts of mine has more holes for spring setting. But I might be wrong. Could be another keyboared.
Hadn’t it open up for decades now

15

I’m in touch with Kevin, hopefully i will get an Opto-key for this beauty. :stuck_out_tongue:

As i mentioned before, aside from one or two scratchy pots, everything is working on my Mini. Should i check for something else, recap, whatever, or just leave it like this? If ain’t broken don’t fix it, it know, but if i can do something to avoid bigger issues, now is the time.

16

I recommend replacing all electrolytic caps, but if you don’t do this, at least check that the fuses installed are the correct values.
If something dies in the Mini, you’ll appreciate a fuse blowing and not something like a power transistor.

17

Thanks for your input Kevin

Now, what about these small holes in the wood cabinet..?
Intriguing… :unamused:

18

Looks very much like Termites damage…

19

Oh s***, are they eating my mini? :smiley:

I was thinking in refinishing the cabinet, now i have bigger arguments i guess

20

If there are still some in your Mini, I would have it fumigated ASAP, otherwise your synth might not be the only thing they eat… :open_mouth:

I’m not a bug specialist, but I’ve seen this kind of thing before, and it was caused by Termites.

A quick search on Google with pictures results of Termites damage show that I might be right, unfortunatly…