Restoring Opus 3...a few issues.

[kaseijin]

Picked up a box of Opus 3 (cardboard box, various PCB's, disassembled chassis, bag full of screws and various other bits) for a good price recently, and began cobbling it all together with the intention of not only gigging it, but making it functional and attractive as well. After some work, I got it all back together, and it made noise, but it was fairly unpredictable, as It had a pretty good case of foam gunk all over the control board, and several of the sliding pots were stuck or otherwise inoperable. I ordered a new set from Technology Transplant, and got to work soldering them in. (incidentally, only 22 of the 25 sliders arrived, and one of the 22 that did was audio taper instead of linear...so some manual de-gunking still had to be done).

Now, pretty much everything works, and I can begin isolating individual issues to address. Here's a laundry list:

* D#4 does not generate any sound. Further, the other D# keys all sound a bit peaky...as if perhaps they are playing not only the note they are meant to, but also the next D# up.

* Attenuator mode 2 is...strange. If I power the unit on with the attenuator in mode 2, it won't make sound until I toggle back to mode 1. If I leave it on for a while, mode 2 makes sound...but it sounds identical to mode 1. I can't tell a difference. The lag between powering on and mode 2 making sound has me thinking capacitors.

* VCF A/D/S/delay does nothing that I can tell. Well, mostly. If I set the filter to be really resonant, the sustain slider can kind of be used to tweak the cutoff. I'll double check the sliders, but what else could cause this?

* There are some interesting volume differences in that the brass section seems quite loud, the organ section has a pretty wide volume range, and the strings section -- while all working properly -- seems quite quiet.

* Attenuator attack slider does not work. Could be the part itself. Will check, but what else should I also look at?

* Keys are pretty clacky feeling compared to my other boards...but the they are even (no warp) and the bushings all look good. Should I go ahead and replace bushings anyway? Would that help? Was this just a more cheaply made board than others of that era?



If you've read this far, thanks! And here's some good synth-resto porn:

board before:


board after:


chassis being clamped:


cheek sanded and stained (ended up using a light maple stain instead of natural):

[Kevin Lightner]

* D#4 does not generate any sound. Further, the other D# keys all sound a bit peaky...as if perhaps they are playing not only the note they are meant to, but also the next D# up.

You're going to want to look into the 5823 dividers for this problem.
I might have some originals or substitute divider boards around, but you should first find out how many you'll need, then go searching.
Some models might also use TDA1008 dividers.

You can use a scope to locate bad dividers or simply use an audio probe with a resistor inline (100K is fine.)
If you probe a divider's output pins, you'll be able to hear the unmodified "raw" signals directly and this can help speed up troubleshooting.
Remember, if a high octave divider fails, all the notes below that divider will also have problems.
So always check the highest notes first, then work your way down.

Sorry that I can't help out more, but it's easier for me to do the actual work than it is for me to type things out.
However I will offer that env problems can often be due to bad 4007 chips.

Good luck!
K

[kaseijin]

Thanks for the reply!

I sourced a couple of TDA1008 divider IC's from ebay. Went ahead and picked up a few of them, just in case...though I'm a bit worried (since the fault seems to be originating in the top octave) that it's the MO83 TOS chip. Fingers crossed!

Thanks for the tip on the 4007s, too! Also, can a 4027B be used in place of a 4027BE? What's the difference in the suffix?

Anybody have a good source for non-P&R key bushings?


(adding tip for anybody else who may be following along)
I can not recommend enough using retr0bright to reverse yellowing of plastic. The pitch wheel on this Opus had a pretty deep line where the exposed area had yellowed badly. I mixed up some retr0bright, soaked it in the sun for 4 hours, and now it's like new:

Before soaking:


After soaking:


No more yellow!

[Kevin Lightner]

though I'm a bit worried (since the fault seems to be originating in the top octave) that it's the MO83 TOS chip.

I have some of these, but you're not gonna like the price.

can a 4027B be used in place of a 4027BE? What's the difference in the suffix?

I can't say exactly what the E designation means.
Suffixes can vary with rev, manufacturer and other criteria (protection diodes, buffering, etc), but you'll probably be fine here with a B.

Anybody have a good source for non-P&R key bushings?

Obtain some teflon tubing in the right diameter and cut it using a tubing cutter or scissors.
Same thing Panasonic and others used.

[LWG]

Hello,

You may want to consider one of these:

http://flatkeys.co.uk/MK50240.html

Regards,

L

[Kevin Lightner]

LWG,

Thanks. Those are interesting.
I wonder if the frequencies are locked or asynchronous?
If the latter, it could actually fatten up the sound of the Opus some.
The price however is more than some people charge for original 50240 / M083 chips.
If the original poster actually has a bad M083 TOG, I and others could probably beat the price of this device.
Today's UK-US pound/dollar conversion makes it about $67, not incl VAT and shipping.

But again, if the freqs it produces aren't locked to each other, it might actually sound a bit better with one of these critters.
It certainly makes me curious how a Polymoog might sound if one or two of these were used instead of their TOG chips.

[kaseijin]

Replaced the TDA1008 IC that routed the D#'s, and that fixed the keyboard issue. Very thankful that it wasn't the MO83!

Next thing that I think I will tackle is the filter. So here's what's up:

Attack and Decay don't really seem to do much of anything at all.
Sustain...kinda sorta does something. It affects the sound only when super-resonant.
Final Decay toggle does nothing that I can tell.
Contour Amount sounds like it affects the cutoff frequency.
Cutoff and Resonance both work normally.

I'll put in an order from Mouser for a few new 4007 IC's today, as well as a couple of transistors that the service manual says may be at fault. Anybody have any other tips?

Also have a really very basic question: The screws that fasten the control board to the chassis... I know nothing about sizing screws or even types of screws (beyond countersunk vs. well...not countersunk). I want to replace all of these screws as well as the two that fasten the pitch wheel. Anybody know offhand what size/style i should get?

[kaseijin]

Speaking of those transistors...

Q4 and Q5 on the board are NPN Darlington D16P1 Transistors, which appear to have been discontinued.

Anybody know of a suitable replacement?

[EMwhite]

Also have a really very basic question: The screws that fasten the control board to the chassis... I know nothing about sizing screws or even types of screws (beyond countersunk vs. well...not countersunk). I want to replace all of these screws as well as the two that fasten the pitch wheel. Anybody know offhand what size/style i should get?

I have an Opus 3 in pieces as well and would be happy to measure/take pictures for you this weekend.

Mine works 100%, well sliders and pots are crap but everything except for final sustain seems to work as far as I know, but I've disassembled it and cleaning up circuit board and the gunk/foam. I think a prior owner tried using gasoline or some sort of kerosine to try and dissolve the foam, at least it smelled of that and there was a liquid film across the board that I'm sure would have shorted something out if I kept playing.

Could use some advice on where to get sliders or what type of solution to use in order to clean. The technology transplant 'kit' seemed suspect at best (overpriced and a lack of information which lead me to believe that they haven't put alot of thought into sourcing the correct sliders for every single component).

Thanks.

[kaseijin]

For the sliders, I got the kit from Technology Transplant. The quality of the parts seems fine. They are all clean, they all work well, and they are bagged and labeled according to the parts list in the service manual, which is rather handy.

The downside was in dealing with the seller...maybe. I'm honestly not sure? Here's how things went down:

I placed the order, and had to get a custom invoice from CY because my order also included a few random parts for another keyboard. I was invoiced and paid, and received no further communication. CY seemed friendly when we did communicate, but I got the definite impression that his English was not the strongest. Can't blame the guy for that, he's in Hong Kong, after all.

Three weeks went by and I decided to email just to see if the order had shipped, but I didn't hear back. During this time, I found some posts online where people said that delivery from Technology Transplant was typically about a month, so I decided to be patient. Four days later, I had my parts. Delivery time was within a month, but I could not help noticing that the ship date was the same day that I sent my email query. Coincidence? Who knows? I got the parts, and am basically happy.

The one big issue for me was that the part kit was supposed to be 25 sliders, and I received 22. That's three short. And actually, I was short four... because a group of four sliders had been replaced in the bag with one slider for a Concertmate MG-1's glide control, which had the right resistance but was audio taper instead of linear.

So in the end, I still had to clean and rebuild four sliders.

Since then, I have noticed that Mouser.com has all the same sliders, but they do sell by length...so I imagine you'll have to measure the length physically and then match resistance and taper with what's in the service manual. Prices seemed about comparable to what the Technology Transplant kit broke down to.

If you want to sink the time and effort, you can rebuild the sliders for a lot less money than buying new ones. I just decided it wasn't the effort. Take them off the board (note the direction they were mounted -- some of them can be flipped) and, using a small screwdriver and set of needle-nose pliers, gently bend back the brads that hold the backing in place. Then take it all apart, noting how everything goes together.

DeOxit works for cleaning the contacts and other interior bits. To remove the tar gunk from the exterior or the sliders, I soaked those metal parts in ChemTool for a while -- ate everything right off. Rinsed them off well, lubed up all interior parts (being sure to get the sides and top of the plastic piece to ensure smooth movement) with Luberex, and clamped it all back together.

A lot of work, but nothing terribly difficult.


EDIT: Don't get any plastic in the ChemTool. It will eat anything that is not metal.

ANOTHER EDIT: I made a second order to Technology Transplant for new slider caps, and mentioned in my order about the missing sliders. CY was very polite and prompt, and emailed me to apologize for the oversight and let me know that they would be included in this order. He seems an alright guy in my dealints -- I'd warrant that a lot of people's issues with TT are simply due to language/cultural barrier.

EDIT^3: Received plastic knobs from CY, and the missing sliders were in there as promised!

[EMwhite]

You had a question about the general hardware. I have a few pics for you but for whatever reason, I'm above my quota?

If you send me a PM, I'll email you directly.

The long story short is that my Opus has also been taken apart and put back together using somewhat non standard hardware specifically on the four bottom screws and the two back screws.

But the main panel screws use two locknuts and the front has a 3/4" standoff (I have the actual measurement written down and will get that for you when I get home tomorrow).

Meanwhile, thanks for the info on the cleaners, etc. I managed to find Deoxit from Radio Shack but to tell you the truth, it seemed to dissolve any lubricant in the slides. I was wondering if anybody knows if "Super Lube" which is an inert pfte (synthetic teflon) might work? I use them on stepper motor contacts and it works very well, doesn't attract dust, etc.

Thanks.

[kaseijin]

The DeOxit is really just for cleaning the contacts -- your contacts with sparkle and shine, but it will absolutely remove any old lubricant on there.

Thus the Luberex afterward. It's a white dielectric grease that you can lube your sliders up with before reassembling. It works really well, and makes your sliders feel all buttery and new.

[Kevin Lightner]

I don't much like the new (white) Luberex, but their old (now banned) brown goop was great on sliders.
Certain automotive greases can be good too, but it can be a lot of trial and error buying and trying.
Sometimes a thick grease along with just a drop of fine teflon lube can get just the right feel too.

[kaseijin]

Well, I replaced the 4007, 4001, and two 4053 IC's on the VCF....and the 4007 on the articulator attack...and....nothing. Well, mostly nothing. Here's what it's doing:

VCF emphasis and cutoff work perfectly. But then, they always did. Contour amount now appears to work properly, instead of simply affecting cutoff. Service manual says this issue should have been transistor Q4 or Q5, but the new IC appears to have resolved it.

VCF final delay switch still appears to not work, but it could just not be evident due to the articulator mode switch not working.

VCF attack does absolutely nothing.

VCF sustain and decay appear to do...something. Sustain seems erratic, though.

Modulation delay slider does nothing.

Articulator attack slider does nothing. (thinking maybe capacitor C5)

Articulator mode switch does nothing. (since I already swapped the 4007 IC here, the next step is to check capacitor C3, according to manual)

There is some bleed through of brass into the VCF when the Brass/Organ fader is set fully to Organ. I can set it fully to Organ, and still hear pitch changes when selecting brass frequency.


It seems to me that these are potentially all capacitor issues, but daaaaaaaaamn, that's a lot of bad caps.

[kaseijin]

Finally figured out the last of the issues last night!

As of last night, I had still been experiencing a nonfunctional VCF envelope, nonfunctional articulator mode switch and attack fader, and nonfunctional modulation delay. I practically rebuilt the entire VCF section...new IC's new capacitors, new faders, new diodes, and still nothing. It was maddening.

Then I noticed something. If I moved the sustain fader, I could hear the envelope change. Don't really know how to describe it, other than to say that the envelope would just sort of 'catch up'...but nothing was really triggering it.

I started to think that maybe I was looking at my problems in the wrong way. I was seeing three different issues in three different sections of the synth...but what if they were all related to key triggering? If none of the envelopes were receiving fresh key trigger information, then that might cause them all to fail in the same way.

Sure enough. U3 on the control board -- the 40106 Hex-Schmitt Trigger -- was faulty. Replacing that one chip fixed *everything*.

I suppose the up-shot of it being a bit of a pain to track that down would be that I now have all new capacitors, 4007's, 4001's, 4053's, and several new op-amps on the control board. It should last for a good long while, now!

So everything is functioning fine. All that's left now is maintenance work. I figure the next step will be to re-cap the power supply/keyer board.


Here's the mostly-finished Opus:



One last question: I have heard that stiff felt is a good replacement for that horrible foam, to place between faders and chassis...both to just clean up the look of open sliders, and to keep dust/cat hair/etc out of them. I have also heard that stiff felt just sheds.

What would be a good replacement material, or should I even bother? Anybody?