[sdiy] Minimoog tuning questions

[Julien Delgoulet]

When you look at the voltage at the connection between R163 & R180 do you get 10volts ?

Envoyé de mon iPhone

Le 9 avr. 2015 à 20:29, Eric Frampton <eric at ericframpton.com> a écrit :

> Hi all -
> 
> I’ve had another Mini come across my path. This one’s S/N is in the late 4000’s. It came to me with a bunch of problems, including some well-intentioned but (ultimately) incorrect mods done by previous techs that I’ve been going through and fixing/un-doing. I’m down to, I think, the last problem, but it’s a biggie: all three oscillators, at the center of their Range pots, to want to speak roughly an octave too low.
> 
> This is the older oscillator board, not the newer one.
> 
> I’ve checked the PSU, got a solid +/- 10.0V at the osc. board
> Cleaned all edge connectors
> Checked the output of the keyboard, and it starts at 0V on the low F and works up by roughly 1V/oct from there, as it should
> All 3 oscs scale correctly at any octave setting (it’s the ranges that are off)
> The octave switch transposes correctly with all 3 oscs (they’re still all an octave too low, but switching the footage makes a 1 octave jump as it should)
> This one does not have the deadband mod on the pitch wheel, but I’ve double checked and the pot measures 15K to ground at center detent
> This one does have the buffer board installed
> This one does have the R/C network installed on each osc.
> One of the mods the previous tech had done was to install sockets for all the 741’s. Before removing all the sockets, I tried swapping 741’s around to see it made any difference; no change.
> One SG3821 is socketed; I tried swapping with a 3046, same kind of problem
> 
> I’m seeing 5V on pin 6 of IC1, IC4, and IC6.
> 
> Fortunately I have a working Mini of my own to compare against (s/n in the 1700’s, also with the older board). However, mine -does- have the deadband mod but -not- the R/C network, which seems to be making some of the voltages - notably, the outputs of IC3, IC5, and IC10 - not match between good and bad boards at all.
> 
> Putting the bad board in mine, it speaks roughly an octave low. Putting my good board in the bad machine, it sounds at roughly at the correct octave. So I think it’s safe to say the problem is on the board itself.
> 
> Since all three oscs are low, I know I could just offset the pitch wheel until I got in the ballpark then calibrate from there, but that seems like cheating - I’d really like to figure out what’s going on. I’ve tried using the techniques you all taught me on the last go-around with another mini, but apparently my current-fu is not good yet.
> 
> Help?
> 
> e
> 
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