Vintage Synth Repair

Dear forum members,

I have a late Moog Prodigy, model 336A.

Currently, the Pitch Wheel transposes 9 semitones up (C4 - A4) and 11 semitones down (C4 - C#3). According to the manual, the Pitch Wheel range should be “Greater than ± perfect fifth”.

Also, the Modulation Wheel (in it’s maximum position), while in Oscillator Modulation, transposes 17 semitones up (C4 - F5). According to the manual, it should transpose up to 12 semitones only. (And if I remember correctly, the Mod Wheel used to work correctly before)

As far as I can see from the part numbers, printed on the installed pots, they are original Moog parts: 10K Linear pot for the Pitch Wheel and 10K Special Taper for the Modulation Wheel.

I'm not sure if these types of pots are right for the Prodigy: I have the Prodigy parts list in PDF, but there's no information about the types of pots for the wheels. The schematics only says "10K pot". And Syntaur.com sells the same part for both Wheels for the Moog Prodigy.

I would greatly appreciate any information or hint. I'm trying to figure out if the problem is in the pots or the source of the problem is somewhere else.

Thank you,

Gregory

If mine had that problem, I would begin by going through the entire alignment procedure.

----- Original Message -----
From: "gk.box@... [vintagesynthrepair]" <vintagesynthrepair@yahoogroups.com>
To: vintagesynthrepair@yahoogroups.com
Sent: Tuesday, July 26, 2016 10:27:29 AM
Subject: [vintagesynthrepair] Moog Prodigy: Pitch and Mod Wheels strange ranges


 












Dear forum members,








I have a late Moog Prodigy, model 336A.








Currently, the Pitch Wheel transposes 9 semitones up (C4 - A4) and 11 semitones down (C4 - C#3). According to the manual, the Pitch Wheel range should be “Greater than ± perfect fifth”.








Also, the Modulation Wheel (in it’s maximum position), while in Oscillator Modulation, transposes 17 semitones up (C4 - F5). According to the manual, it should transpose up to 12 semitones only. (And if I remember correctly, the Mod Wheel used to work correctly before)












As far as I can see from the part numbers, printed on the installed pots, they are original Moog parts: 10K Linear pot for the Pitch Wheel and 10K Special Taper for the Modulation Wheel.








I'm not sure if these types of pots are right for the Prodigy: I have the Prodigy parts list in PDF, but there's no information about the types of pots for the wheels. The schematics only says "10K pot". And Syntaur.com sells the same part for both Wheels for the Moog Prodigy.










I would greatly appreciate any information or hint.  I'm trying to figure out if the problem is in the pots or the source of the problem is somewhere else.








Thank you,


Gregory

Hello Gregory,

I looked up the schematic and, as far as I can tell, both pots are connected to +12 & -12v at their ends. Have you checked these voltages? Perhaps a power supply issue, shorted regulators or something?

It is difficult to imagine how the pots' values might have changed to cause the issue as you have described.

Absent finding original 'special' taper replacement pots, linear is the only sensible answer for a normally-centered application. (Up 2 & down 8 semi tones wouldn't work well!)

Check the + & - 12v supplies with a meter first.

BR,
-Hugh