[sdiy] Prophet 5 rev2 conundrum

Luís Marka luis.marka at gmail.com
Wed May 3 00:17:00 CEST 2023

Not sure if it helps since the electronics are different, but I had an 
issue with autotune in 2 voices on my Memorymoog clone. Turns out the 
Glide time trimpots for those voices was adjusted too high, and the CV 
injected into the VCOs was showing a slope when switching between the 0 
/ 5 / 10V CV during the autotune routine, messing up the frequency 
counter and making autotune impossible. Readjusting the trimpot solved 
the problem (in the Memorymoog, each glide trimpot affects 2 voices). 
Maybe you could investigate how that particular voice reacts to 
frequency CV during autotune?


On 2023-05-02 2:11 p.m., g m montalbano via Synth-diy wrote:
> I've been working on these for twenty years, and thought I'd seen 
> pretty much everything that could go wrong with them.
> Now, I have one that works perfectly except for the fact that it will 
> not go through the tune procedure, either at powerup or when the Tune 
> button is pressed.
> The confusing part is that the fault has been narrowed down to the 
> voice board: if I swap in a working voice board, the unit functions 
> correctly; if I install this voice board in another unit, the problem 
> follows.
> As far as I can see, the ONLY parts on the voice board that relate to 
> tuning are the two 4051 multiplexers (U423 and U428) and the LM311 
> comparator (and its associated resistors & caps). All of these 
> components have been replaced; traces and resistors have been checked 
> &  measured. All traces to the 60 pin connector between the CPU and 
> Voice boards are good, as is the 60 pin cable.
> EVERYTHING is there, and everything works correctly except for Tune.
> I've been hitting my head against this for a couple of weeks, and 
> would appreciate any suggestions as to where to look.
> Thanks.
> ~GMM
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