Vintage Synth Repair

This is my first post to this group.

I'm having a couple of problems with my MicroMoog that may, or may not be related. I'm a competent tech, however, I mostly work on pro audio equipment, so I'm afraid I may not speak synthtalian well enough to diagnose the problem, or properly identify it in the service manual.

Problem #1:

Using the switch/knob positions from the 'Sample and Hold' template in the manual, I'm not getting the cool randomization in the S&H AUTO position on the mod source switch. I DO get the 'choppy' sound that varies with the RATE knob, but the mod wheel just acts like a pitch bender.

Problem #2:

When the mod source knob is in the S&H KEYBOARD position, pressing any key does not even give me the 'choppy' sound that I'm getting in the S&H AUTO position... it's just a continuous note. The mod wheel also acts like a pitch bend wheel, just like the first problem.

I AM getting the +/-14V at the junction of R802 and C909. My scope IS showing some kid of noise source on pin 3 of IC902, but I'm not sure if it's white, pink red or purple, nor what level it's supposed to be at. I'm also not sure what I'm supposed to be seeing at the junction of IC902 pin 6 and the gate of Q901. When probing the 'source' leg of Q901, I'm NOT getting the random +/-5V waveform that's shown on the schematic. I've swapped out IC902, Q901, C909 and C908. For the sake of full disclosure, I replaced Q901with a NTE467 instead of the stock E112. I have lifted and checked every component in the Sample & Hold section that's shown on the schematic around IC902 and Q901. I have also done continuity checks between all of the components, on the component legs (as opposed to just probing the traces), and all is well there. I've also done continuity checks 'through' the switches, and they are working as expected.

I'm spinning my wheels, so I'm afraid that I might be troubleshooting the wrong section of the synth, or, as the manual suggests that IC902 may need to be specially selected to work properly in this circuit.

My best guesses at what may be causing the problems are:

1. The noise source at pin 3 of IC902 may not be at the correct level or color.

2. The pulse feeding the control input (pin 5) of IC902 may not be at the correct level.

3. Q901 may need to be a 'true' E112 (instead of a NTE467) to function properly.

4. IC902 may need to be specially 'selected' to function properly.

Alternative 4, is my guess.
The micromoog (and the multimoog) needs very specially selected CA3080
chips in various places.. I have run into this problem, and it was
only when I put in an old stock chip (and not a new one) that the
function came back to life.




tw.




Den 14. feb.. 2017 kl. 06.30 skrev dolguin@...
[vintagesynthrepair]:


>
>
> This is my first post to this group.
>
> I'm having a couple of problems with my MicroMoog that may, or may
> not be related. I'm a competent tech, however, I mostly work on pro
> audio equipment, so I'm afraid I may not speak synthtalian well
> enough to diagnose the problem, or properly identify it in the
> service manual.
>
> Problem #1:
> Using the switch/knob positions from the 'Sample and Hold' template
> in the manual, I'm not getting the cool randomization in the S&H
> AUTO position on the mod source switch. I DO get the 'choppy' sound
> that varies with the RATE knob, but the mod wheel just acts like a
> pitch bender.
>
> Problem #2:
> When the mod source knob is in the S&H KEYBOARD position, pressing
> any key does not even give me the 'choppy' sound that I'm getting in
> the S&H AUTO position... it's just a continuous note. The mod wheel
> also acts like a pitch bend wheel, just like the first problem.
>
> I AM getting the +/-14V at the junction of R802 and C909. My scope
> IS showing some kid of noise source on pin 3 of IC902, but I'm not
> sure if it's white, pink red or purple, nor what level it's supposed
> to be at. I'm also not sure what I'm supposed to be seeing at the
> junction of IC902 pin 6 and the gate of Q901. When probing the
> 'source' leg of Q901, I'm NOT getting the random +/-5V waveform
> that's shown on the schematic. I've swapped out IC902, Q901, C909
> and C908. For the sake of full disclosure, I replaced Q901with a
> NTE467 instead of the stock E112. I have lifted and checked every
> component in the Sample & Hold section that's shown on the schematic
> around IC902 and Q901. I have also done continuity checks between
> all of the components, on the component legs (as opposed to just
> probing the traces), and all is well there. I've also done
> continuity checks 'through' the switches, and they are working as
> expected.
>
> I'm spinning my wheels, so I'm afraid that I might be
> troubleshooting the wrong section of the synth, or, as the manual
> suggests that IC902 may need to be specially selected to work
> properly in this circuit.
>
> My best guesses at what may be causing the problems are:
> The noise source at pin 3 of IC902 may not be at the correct level
> or color.
> The pulse feeding the control input (pin 5) of IC902 may not be at
> the correct level.
> Q901 may need to be a 'true' E112 (instead of a NTE467) to function
> properly.
> IC902 may need to be specially 'selected' to function properly.
>
> Any insight or technical expertise on these problems would be
> greatly appreciated.

>
>


Terje Winther
terje.winther@...
http://wintherstormer.no/

I had the same problem and i change a transistor in the s&h circuit
And everything came back to normal


Sent from my iPhone

> On Feb 14, 2017, at 12:30 AM, dolguin@... [vintagesynthrepair] <vintagesynthrepair@yahoogroups.com> wrote:
>
>
> This is my first post to this group.
>
> I'm having a couple of problems with my MicroMoog that may, or may not be related. I'm a competent tech, however, I mostly work on pro audio equipment, so I'm afraid I may not speak synthtalian well enough to diagnose the problem, or properly identify it in the service manual.
>
> Problem #1:
> Using the switch/knob positions from the 'Sample and Hold' template in the manual, I'm not getting the cool randomization in the S&H AUTO position on the mod source switch. I DO get the 'choppy' sound that varies with the RATE knob, but the mod wheel just acts like a pitch bender.
>
> Problem #2:
> When the mod source knob is in the S&H KEYBOARD position, pressing any key does not even give me the 'choppy' sound that I'm getting in the S&H AUTO position... it's just a continuous note. The mod wheel also acts like a pitch bend wheel, just like the first problem.
>
> I AM getting the +/-14V at the junction of R802 and C909. My scope IS showing some kid of noise source on pin 3 of IC902, but I'm not sure if it's white, pink red or purple, nor what level it's supposed to be at. I'm also not sure what I'm supposed to be seeing at the junction of IC902 pin 6 and the gate of Q901. When probing the 'source' leg of Q901, I'm NOT getting the random +/-5V waveform that's shown on the schematic. I've swapped out IC902, Q901, C909 and C908. For the sake of full disclosure, I replaced Q901with a NTE467 instead of the stock E112. I have lifted and checked every component in the Sample & Hold section that's shown on the schematic around IC902 and Q901. I have also done continuity checks between all of the components, on the component legs (as opposed to just probing the traces), and all is well there. I've also done continuity checks 'through' the switches, and they are working as expected.
>
> I'm spinning my wheels, so I'm afraid that I might be troubleshooting the wrong section of the synth, or, as the manual suggests that IC902 may need to be specially selected to work properly in this circuit.
>
> My best guesses at what may be causing the problems are:
> The noise source at pin 3 of IC902 may not be at the correct level or color.
> The pulse feeding the control input (pin 5) of IC902 may not be at the correct level.
> Q901 may need to be a 'true' E112 (instead of a NTE467) to function properly.
> IC902 may need to be specially 'selected' to function properly.
>
> Any insight or technical expertise on these problems would be greatly appreciated.
>