Minimoog Model D one sound issue

S

Stanley-Sequencer

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Hi all, I'm new here...

I have purchased recently my second Minimoog Model D.
The first one Ser. No. 5xxx works perfect, the second one Ser. No. 3xxx had no sound. I have found one non-working capacitor 50V 10uF - replaced - it works! But....

If one key pitched it doesn't matter which one - I hear only and always the same sound. The busbar was cleaned, all contacts - the same problem. I have connected my first Minimoog (which works perfect) over cinch jones - the same problem.

68781-4fa064e4675432e7827b5260338eb472.jpg

What I also noticed - no changes in sound by these positions (attached photo marked with red), but I think it can't depend on it.

All other switches, buttons, pots etc. work.

68780-06f5835a80d61cf5237659a2a57b0999.jpg
 
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S

Stanley-Sequencer

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Thanks for your reply.

For all three as marked in red circles.
Standard sound is coming without any pulsation.
 
S

Stanley-Sequencer

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Well, the first problem I have:

I hear the same pitch / note let's say "B" by pressing any keys on keyboard.
I press C - hear "B", I press "E" - hear the same "B" note. I go to another octave press "G" there - again the same "B" note etc. and this issue I have by all keys if I press.

The second problem:

OSC 1: no changes in sound if I switch between square, wide rectangular or narrow rectangular (as per red mark circles on the pic above).
The first three - work well: triangular, sawtooth-triangular, sawtooth.

All other things on Minimoog work well.
 
ppg360

ppg360

fummdich-fummdich-ratata
Did you re-insert all plugs properly, and did you make sure there is no corrosion (or cracked connectors, or broken leads respectively)?

Did you clean the contacts into which the PCBs are inserted? When corroded (or making bad contact because the spring-loaded contacts have lost their tension), they can play some silly buggers on you.

Before you dispose of this old junk, send it my way (for spares etc.)... I'll be happy to pay shipping costs :P .

Stephen
 
fanwander

fanwander

*****
no changes in sound if I switch between square, wide rectangular or narrow rectangular
Please do not answer "it does not change". I did don't ask "Does it change?".

So once again (it seems to be difficult to understand this question):
What does it sound like, if you set it to Square; does it sound like Saw, triangle or what else?
What does it sound like, if you set it to Wider rectangular; does it sound like Saw, triangle, or square, or what else?
What does it sound like, if you set it to narrow rectangular; does it sound like Saw, triangle or what else?

Please answer all questions.
 
S

Stanley-Sequencer

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Thanks fanwander

I will test it again today and get back to you.
One question before I do it: does this problem with OSC1 associate with my another issue - one note plays by all keys?
 
S

Stanley-Sequencer

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To ppg360

As I said I have connected my first Minimoog (which doesn't have any probs) to the second one via cinch jones and had the same problem with "one note playing"
This exclude the problem with PCB or bad connection I think
 
Thomasch

Thomasch

MIDISynthianer
@Stanley-Sequencer
Best thing you could do, is to record an audio sample of the 3 switch positions, and post it here.
 
fanwander

fanwander

*****
One question before I do it: does this problem with OSC1 associate with my another issue - one note plays by all keys?
I am not too deep in the minimoog schematics, but on a first look: if the -10V supply is faulty, then this could apply to both problems.

But the keyboard-problem looks/sounds/reads ( ;-) ) to me more like some mechanical issue.
 
S

Stanley-Sequencer

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Sound 1

Sound 2

Yes, I thought the best solution to solve the prob will be to record audio.

Well, what I set yesterday... 30 Min - warm up - then 20 Min testing/playing.
Result: sound changes by playing the different keys on keyboard but with big delay if I play the last key left then jump to the last key right - it needs time till the correct tone come.
This comes if I use different OCS and settings.

As for OSC1 by square, wide rectangular or narrow rectangular - no sound!
 
swissdoc

swissdoc

back on duty
Regarding the no difference in sound for all the three PW settings and the sound to be very triangle like, I would assume that the comparator LM393 IC 8A is defect or something broken on the rotary switch. This would be for the new OSC board. In case of the old one, that function should be in Q11 2N4058 and Q12 2N3392 or the rotary switch.

About the glide, which is audible: Is glide engaged? Would be strange, if there was glide on OSC1 but not on OSC2 and OSC3.
 
S

Stanley-Sequencer

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Glide is up and down... (but slowly) sometimes a little bit quicker if I pitch the same keys many time

If I have to make some tests else by specific settings please let me know
 
fanwander

fanwander

*****
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S

Stanley-Sequencer

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Yes, you are right, it sounds here without glide but I had a moments where the glide was not so quick.
 
swissdoc

swissdoc

back on duty
Is Glide engaged?
Is that glide effect active for all OSCs or only for OSC1?

Background:
The keyboard circuit provides the Glide as you set it (time) on the panel and engage it in the controller section of the keyboard. This is effective on the CV from the keyboard to the synth. It has to be audible on all the OSCs.
If you have a glide (which cannot be set time wise and engaged that way) on OSC1 only and it is gliding up only, then you have a decent issue on OSC1.

Please provide the SN of your synth and a picture from the backside to see the number of holes for the trimmer. Ideally you would know precisely the revision data of the OSC boards.
 
S

Stanley-Sequencer

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Glide doesn't engaged.
One more audio where you hear the slow glide back to the left end
Sound 3

And photo of the back 68889-47cd1378cbb5b74ced639743b3fc1aa6.jpg
Ser. No. 3xxx
 
S

Stanley-Sequencer

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swissdoc.. yes this is that number and I know about Lord of Mini, but how to settle the problem I have?
 
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swissdoc

swissdoc

back on duty
We need to know, which Osc-Board you have, since there are plenty of variants around. Just some examples:





 
swissdoc

swissdoc

back on duty
Your OSC Board should look like the first blue one. The two 14 pin DIL chips should be LM3046. If socketed you could easily swap them. If the glide error moves from OSC1 to OSC3, then you just need a new LM3046. I suspect the glide problem to come from the LinLog converter for OSC1.

The PWM Problem I would suspect to sit in Q11 2N4058 and Q12 2N3392 or the rotary switch.
 
swissdoc

swissdoc

back on duty
Cool, so my guess was correct. I would remove the board (ground yourself), check all solder points visually, clean the contacts from board to synth with 2-Propanol, do the same with both LM3046 (take great care to not bend the pins). Test. Maybe it helps already. Next step, swap the two LM3046.

If this is not fixing it nor showing a dead LM3046, then you need test/measurement equipment.

Peek visually into the rotary switch and check for broken wires etc.
 
swissdoc

swissdoc

back on duty
Just as comment, the potentially broken LM3046 would attribute only to the strange VCO1 glide. Just another idea: If you have a DMM measure the DC power rails under load and compare to voltages given in service manual (GIYF). If you have an oscilloscope, check the ripple on the DC power rails.
 
S

Stanley-Sequencer

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One problem solved

Bad contacts were found here... OSC1 and OSC3 work at all positions now

68993-a09f3185465ff0aa75677683ae6e76fc.jpg

But the second problem remains, furthermore I noticed that the glide from left ot right and from right to left exists (as per my previous audio)

If the OSC3 control is "off"
68994-2a7515cc0f6682735688610496e404d8.jpg
Minimoog plays the same note at all keys if the OSC3 control is "on" - the sound glides slowly.:sad:
 
 


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