OPUS 3 purchased new in 1981. Now selling, but ISSUES

[Overthere]

Hi all. This is my first post. I purchased my Opus 3 in 1981, and except for some minor use during the first year or two, it's been 'resting' in a cool, dry storage environment. I want to sell it now, and I assumed it to be in excellent condition until yesterday...

Everything seems to work properly except for the Modulation section. I'll put up a short video on YouTube to demonstrate this issue, and will link to that ASAP.

The Modulation section is switchable: VCF / OFF / FM. I hear no Modulation effect unless the AMT and RATE faders are maximized (the DELAY fader appears to work properly). When switched to 'VCF Mode", a sustained musical note 'glitches' 76 times per minute: a minor pop and the pitch drops out for a moment. When switched to "FM Mode", a sustained musical note 'dips' 76 times per minute: as if rocking the pitch wheel slightly.

I've made a deal with an international buyer based on the Opus 3 being in proper working order. I need advice as to what's involved in correcting this. This synth has never been serviced so the black foam is still under the control panel. Is there a chance that removing the foam might resolve this problem?

Thanks

[Overthere]

Here's a link to a YouTube video demonstrating the symptoms:
http://www.youtube.com/watch?v=QJ6T1xay5VA

The video is just 1:36 in length.

Any suggestions on how to correct this are much appreciated.

Thanks

[moogsaurus]

check U8 (3080) controls MOD rate on top slider board,also U7B Lm358 which is a dual function chip which also controls mod capabilities and last transistor Q1. These are all soldered in place,so put in a socket (for the IC's and solder in a 2N3904 for Q1. Unfortunately you'll need a signal tracer to "hear" the circuit if you have access to one (any repair shop will have one) switch off power,take off all the top controls,the black foam will disintegrate as soon as you try to peel it from the circuit board (messy!) plenty of room to work on the circuit,just disconnect from the wire plugs

[Mr Arkadin]

Before selling I would take a look at that foam - that stuff becomes the black goo of death after 30 years and needs removing. You may find it has found its way into all sorts of sliders. I ended up replacing all my sliders as there many with goo issues. Pots and switches should be reasonably OK, although may look a bit crappy after scraping the goo off.

[Overthere]

moogsaurus ==

Thanks for the detailed technical reply. I don't have the skills/knowledge to test and replace components as you suggest, but I really appreciate your comments and will pass them along to whatever technician undertakes correcting the Modulation section issue.

I am considering removing the black foam myself though, so at least it won't be a factor (cost) in having service performed.

QUESTION: Is there any likelihood that removing the foam might resolve the issue with the Modulation Amount and Speed pots? My thinking is that maybe the deteriorating foam is interfering somehow, and cleaning it out might restore full operation. Note that the two malfunctioning slider pots operate smoothly, same as the others...

Thanks

[Overthere]

Before selling I would take a look at that foam - that stuff becomes the black goo of death after 30 years and needs removing. You may find it has found its way into all sorts of sliders. I ended up replacing all my sliders as there many with goo issues. Pots and switches should be reasonably OK, although may look a bit crappy after scraping the goo off.

All slider pots seem to work fine, but I am considering removal of the foam myself. I'm hoping it's not too bad (30 yrs of cool, dry storage and no cigarette smoke, etc). And I found an online article wherein the sliders were disassembled and cleaned with lacquer thinner. If problems with the two Modulation sliders looks to be related to the foam, I might try the lacquer thinner approach.

QUESTION: Is it possible to buy just TWO (2) sliders, rather than full sets?

Thanks.

[moogsaurus]

Highlt unlikely its the sliders! you mentioned that there is a fixed cyclical pattern sounding when the MOD is supposed to be working-i'd say its still component failure,worst thing to do with synths is not using them for long periods. Just turning them on after a long time down can cause breakdown issues! Now i've owned my Opus from new,broken twice in that time (keyer chip and string attack) but I secured the original service data from moog around the purchase date. The components are redily available (except for the Reticon chorus belay chips) which are pretty hard to source. But its not a difficult repair,certainly not expensive the components i mentioned are a few dollars (or in my case Scottish pounds)
john

[Overthere]

Highlt unlikely its the sliders! you mentioned that there is a fixed cyclical pattern sounding when the MOD is supposed to be working-i'd say its still component failure,worst thing to do with synths is not using them for long periods. Just turning them on after a long time down can cause breakdown issues! Now i've owned my Opus from new,broken twice in that time (keyer chip and string attack) but I secured the original service data from moog around the purchase date. The components are redily available (except for the Reticon chorus belay chips) which are pretty hard to source. But its not a difficult repair,certainly not expensive the components i mentioned are a few dollars (or in my case Scottish pounds)
john

Many thanks, John. It's very gratifying to receive technical advice from a helpful, knowledgeable person as far away as Scotland (or is it me that's far away here at the center of the continental U.S...?) Either way, I appreciate the information, and am glad to know my buyer will have no trouble correcting this small issue. He wants to purchase the instrument as is, and will have his technician resolve the matter. My Opus 3 included two 8-page fold-out technical documents naming every electronic component and depicting full schematic diagrams of all aspects. I'm sending that and the original Owner's Manual to him with the synth.

Do you need a copy of the two technical foldouts or the User Manual? I'd be glad to furnish them in the furtherance of the sentiment, "What goes around comes around".

Mòran taing, John!

[moogsaurus]

Thanks for the kind offer,but I'm into the opus "long haul" probably leave it in my will! have all the relevant documentation needed for its/my lifetime! its a great synth-way better than any counterpart (korg delta/omni) which i owned previously.not great monetary value-but a very useful synth!
glad to help,think its new buyer will give it a new breath of life!
john