Minimoog Model D, I need some help!

[Guizmo]

Hello everybody,

I’m here because I’m the happy owner of a 1975 model D minimoog with several problems so I need your help…

Firstly, I want to say that I’m not a technician but I’d like to try to repair it myself.

Secondly, I’m french, so excuse me for my english

The main problem my minimoog has, is that there is one single note on the whole keyboard. So, I cleaned the buss bar and keyboard contacts but nothing special happened. When I bought the mini it was in very good condition without corrosion and the buss bars were super shiny.

The second problem (and I think is related to the first) is that OSC 1 and OSC 2 don’t work as they should. OSC 3 seems to work when I switch between LO to 2’ range, but 1 and 2 are TOO high… In LO position the sound produced is audible and playable (don’t forget that I have a single note), but in 32’ the position the sound become too high, like ultrasound, and it increases increasing the range. The sound changes by changing the range position, and all shape knobs seem to work well.

The third problem is that, few keys (8 if I remember well), don’t make a constant contact with the superior bar when they are in rest position. Because the arm who make the link between the piece of plastic with the springs and the key mechanism has been changed and don’t make the job. Do you know if the superior spring has to make a constant contact with the superior bar in rest position ?

Thanks a lot,
Guillaume

[noddyspuncture]

The main problem my minimoog has, is that there is one single note on the whole keyboard.

The Minimoog does actually only play one note, it won't play more even if you try to..!

[Guizmo]

I don't understand...
Are you telling me the minimoog is monophonic ?
If yes, I know that, thanks
What I'm saying is, my minimoog plays a c# on each key of the keyboard, the same single c#, like if he had 1 key and not 44.

[megavoice]

Secondly, I’m french, so excuse me for my english

The main problem my minimoog has, is that there is one single note on the whole keyboard.

First I`d be happy to be able to talk French like you English can do, although French was one of my favourite subjects .

Secondly, if you`d like to play polyphonic on a new Moog you can stand in a row with many other people for waiting `till you`ll get white and grey hair like I have, but not from waiting in this case.......

[zaiusz]

I don't think he means plays one note expecting it poly, but every key plays the same pitch.

You should double check if there is a spring j-wire stuck making contact on the bus-bar, this will make every note play the same pitch.

Otherwise, it does sound like you have more problems if setting different octaves are much higher than they should be. I would suspect the problems you have are attributed to bad 741 ICs-- I would check any of these IC1,4,6,8&9. Also check the CA3046s after this chain- IC2 & 7. They may be SG 3821's depending on the revision, but are interchangable with 3046s. If you change any of these chips you will need to do a full oscillator calibration afterwards.

[Guizmo]

I don't think he means plays one note expecting it poly, but every key plays the same pitch.

Exactly !! That's what I wanted to say ! I requested but I think there was a moderation problem and my answer doesn't appear.

You should double check if there is a spring j-wire stuck making contact on the bus-bar, this will make every note play the same pitch.

There are 3 bars, are we agree that the bus-bar is the single contact bar at the bottom ? If yes, I'm sure that any spring make contact with it in rest position.
As I showed before on the picture, on rest position few spring doesn't make contact on the upper bar, is it a problem ?

Otherwise, it does sound like you have more problems if setting different octaves are much higher than they should be. I would suspect the problems you have are attributed to bad 741 ICs-- I would check any of these IC1,4,6,8&9. Also check the CA3046s after this chain- IC2 & 7. They may be SG 3821's depending on the revision, but are interchangable with 3046s. If you change any of these chips you will need to do a full oscillator calibration afterwards.

, that's gonna be difficult for me I think!

Thanks a lot

[MC]

I don't think he means plays one note expecting it poly, but every key plays the same pitch.

You should double check if there is a spring j-wire stuck making contact on the bus-bar, this will make every note play the same pitch.

Otherwise, it does sound like you have more problems if setting different octaves are much higher than they should be. I would suspect the problems you have are attributed to bad 741 ICs-- I would check any of these IC1,4,6,8&9. Also check the CA3046s after this chain- IC2 & 7. They may be SG 3821's depending on the revision, but are interchangable with 3046s. If you change any of these chips you will need to do a full oscillator calibration afterwards.

Start at the source. The first thing to verify is the POWER RAILS. Then he needs to check if the Keyboard CV is kosher. That circuit is on the contour generator board not the oscillator board.

, that's gonna be difficult for me I think!

Then this would be better left in the hands of a qualified tech. Some things can't be fixed over the net.

[Guizmo]

Thank you, I'm gonna check again the power rails.

Sorry but I still don't have an answer to this question :

As I showed before on the picture, on rest position few spring doesn't make contact on the upper bar, is it a problem ?

If it's a problem that will be the next step of the job.

Thanks

[zaiusz]

Yes sorry I was skipping ahead, verifying the voltage on the power rails is always the first step, and add, do not do this if you are not comfortable working on power supplies or have no experience-- dangerous voltages are present when measuring and can be fatal. Use extreme caution or better yet take it to someone experienced who can do this for you.

But If his osc 3 is in the right range, and everything else is ok except his kcv source on osc 1&2 I would guess one or two of the 741s I mentioned could be the culprit.. And possibly the ca3046 ICs that follow.

I picked up a mini a year ago that had the same issues with ultrasonic waves and untracking oscillators, the problem was right here in the 741s, but yes it could be a number of things but this would be the most suspicious place I would look.

[Guizmo]

Thanks for your answer.

Nobody knows the answer for my question concerning the springs who don't make contact when the keys are not played ?

[zaiusz]

Thanks for your answer.

Nobody knows the answer for my question concerning the springs who don't make contact when the keys are not played ?

I don't know the answer on that one... All I know is that if one of the springs is making contact on the other bus bar it will keep the pitch stuck on a note.

Other than your oscillators do the other functions work ie filter and envelope?

[Guizmo]

Ok thanks !

Filter and envelop seem to work correctly

Thanks

[Guizmo]

Hello everybody,

I post here on my topic, It'll be easier because I've an equivalent project.

I'm actually restoring an Arp Odyssey 2800.
I think I saw (don't know where) a guy putting some silicon grease on this little cap (see my picture).

Do you think I've to put a drop on each ?

Thank you

[thealien666]

I would highly suggest so, yes. Those "dome" are rubbing inside each key, and it will make the action much smoother.
But nothing else than silicon lubricant, since petroleum based grease or lubricant can damage them.

[Guizmo]

Cool thank you ! I'll put a drop of my silicon grease on each !