I have both the model 10 and Model 15 reissues. The 902 on my model 15 suddenly stopped working a while ago, and recently the Model 10s 902 has gone almost silent. The top output is silent, and the bottom output is barely audible.
Is this common with the 902 ? and does anybody know how I might be able to fix them, if its possible with a tech ?
Thanks.
The 902 consists of a sequence of differential transistor amps. Here the schema of my clone simulation, which is equal to the original:
My recommendation is to follow the rabbit into the rabbit hole, meaning following the input signal with a scope up to the outputs. Don’t forget to check the CV processing as well. At the Emitter of Q10 the level must not be too high, as this would close the VCA.
Paul,
Contact Jareth Lackey, SynthPro LLC in Alabama. He has experience with Moog modulars. Or definitely August Worley with the BMF.
Let us know what the problem was. It’s beginning to sound concerning that you have issues with the same module across models like this. I will be on the lookout for issues with mine.
Hope you get this resolved.
Eric
The 902 from the Model 15 just stopped working, no idea why, completely silent. The Model 10 902 suddenly went very quiet. The top output is now silent, and the bottom is barely audible. I have a tech in Germany that I’ll send them over to and report back the diagnosis.
Sorry, I presumed you we’re in the US for some reason. Gerhard would probably do it but sounds like you have it all arranged.
I got them fixed, apparently the 2N4058 PNP silicium transistors had fried on each module. I wonder what did that ? I’m generally sequencing them from a Kenton Pro 2000 MK2 using a jack to Cinch Jones to the EGs but they are gate not S-trig cables (If i remember right) I had the Kenton set to Gate 15V Pull Up as it was giving me the snappy envelopes I like - similar to my Minimoog. Is that too much for the 902s ? has 15v pull up burnt out those parts ?
Paul,
Thanks for letting us know. I really can’t speak with any certainty about the voltages within as that’s a bit out of my scope, no pun intended.
Operator error.
You’re pushing a 15VDC gate into an EG module that is powered by 12VDC and triggered with S-trig. Not only have you exceeded the power rail voltage, you can’t push a V-trig gate into an S-trig input. S-trig requires a short to ground to trigger, and you’re pushing 15V. The “S” in S-trig means “shorting”. Your trigger levels and polarity are wrong, and the EG output - pushed by the 15V gate - probably propagated to the control input of your 902 VCA - also powered by 12VDC - which very likely blew those 2N4058s.
The Moog modules of that era were powered at (+)12VDC and (-)6VDC. You should NEVER exceed the power rails of any electronic circuit, they can act weird or eventually break.
Ah right thanks - since I moved house my cables got mixed up, I just found my jack to CJ cables that are converted to Gate and everything is working fine with the Kenton set to Gate 5v. I’m hoping that is still a safe option ?
Short to ground, not a voltage trigger
But when I use strig on the Kenton and use strig cables the note and off are reversed when I try and play the model 15 or 10 from Logic Pro or a controller keyboard, so there’s a constant drone.
The cables I have are active conversion cables from Moon modular.
