Oberheim OB8 Repair & Calibration

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Oberheim OB8 Repair & Calibration

Postby themilford » Mon Nov 11, 2013 9:46 pm

Ok,

So I have a late model OB8 with factory midi in need of some repair. I received the synth DOA (no output) and traced the problem to the two output CEM3360s and a bad 3080 and replaced those. Now it outputs sound. However It's not calibrating the tuning and filter properly on 5 voices… some voices sound WAY out of tune and tone. The auto-tune shuts off most of the bad voices. Some of the tuning trim pots seem out of whack (an octave too high) and won't bring the frequency down to range manually. A few of the fornt panel controls also seem to be ineffective or jumpy. All the voltage points on the PCB seem to be in spec though. The synth is in beautiful physical condition and does not look to be abused. While I have minor repair skills and a basic understanding of simple electronics I don't trust my ability to desolder faulty parts without lifting PCB traces and further damaging things. I generally repair guitar amps which are a whole other world.

So, I spoke with an acquaintance of mine that is an repair tech at Main Drag. He spoke with the head repair guy who passed on the repair. Apparently he won't work on Oberheim OB8s for some reason. Too finicky I was told.

I know of Three Wave in NJ but I have read of a few bad experiences there… also they are a bit of a hike for me.

I'd love to find a place in Brooklyn… but I can easily get to Manhattan or Queens.

Anybody have a good repair guy in NYC that is well-versed on OB stuff? I'm less worried about price and time and more concerned with a proper and careful repair.

Thanks!
Last edited by themilford on Wed Nov 13, 2013 4:38 am, edited 1 time in total.
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Re: Oberheim OB8 repair New York (5 boros)

Postby themilford » Mon Nov 11, 2013 10:48 pm

I just found and talked to these guys:
http://www.theanaloglab.com/about/

They seem knowledgeable, experienced and reasonable. Anybody here have any experience with them?

I notice they have a few posts on this forum… FWIW.
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Re: Oberheim OB8 repair New York (5 boros)

Postby synthparts » Tue Nov 12, 2013 3:35 am

The OB-8 has about the easiest calibration/tuning procedures ever in an analog synth, did you try it?

http://www.synthfool.com/docs/Oberheim/ ... b8_cal.pdf

The OB-8 is also one of the easiest synths to work on (almost every chip in the synth is socketed and boards are laid out logically and labeled what each section does). If the Main Drag tech can't handle it makes you wonder what they do work on. Maybe he has it confused with the OB-X...
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Re: Oberheim OB8 repair New York (5 boros)

Postby themilford » Tue Nov 12, 2013 4:54 am

synthparts wrote:The OB-8 has about the easiest calibration/tuning procedures ever in an analog synth, did you try it?

http://www.synthfool.com/docs/Oberheim/ ... b8_cal.pdf

The OB-8 is also one of the easiest synths to work on (almost every chip in the synth is socketed and boards are laid out logically and labeled what each section does). If the Main Drag tech can't handle it makes you wonder what they do work on. Maybe he has it confused with the OB-X...


Yeah, ran the calibration a number of times to no avail. But I'll give it another try before I take it to Analog Lab.

Will the calibration sort out inoperable front panel pots? Do the voice board tuning trims really conk out? How robust are the traces on these things with careful desoldering work?
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Re: Oberheim OB8 repair New York (5 boros)

Postby synthparts » Tue Nov 12, 2013 5:58 am

Another thing to try is just re-seating the CEM3340 VCOs on the non-tuning voices. Sometimes the chip pins/sockets get dirty. You can also try swapping the 3340 to another voice to see if the problem follows it.

For the pots you can usually spray some contact cleaner in them and work them back and forth. To get the cleaning inside the pot spray them underneath where the opening is where the legs of the pots come out of the pot and solder into the board.

As far as desoldering parts on vintage synths I wouldn't recommend doing it unless you have a good desoldering station like a Hakko 808.
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Re: Oberheim OB8 repair New York (5 boros)

Postby themilford » Tue Nov 12, 2013 5:56 pm

Firstly… Thank you for your excellent suggestions Synthparts. I really appreciate the advice and I'm sure this will be helpful information to have here.

So, yes. I tried swapping the CEMs a while back. The problem stays with the card. I also cleaned every pin on every socketed chip (on the offending voices). I also cleaned the connectors from board to board.

I don't think I've tried cleaning the trim pots or the panel pots with D5. I suppose that would be a good idea to try next.

I worry a desoldering pump will lift traces… I know you suggest the Hakko desoldering iron… but isn't that the same theory? My EE friends are suggesting solder wick as the safest… they say getting the tip and temp right and not lingering too long on joints should be the most delicate approach.

I've made the decision to attack two repairs this weekend to see if I'm up to the task:

Swap one of the faulty VCO trims with a new one, and swap a faulty pan pot with a replacement. I figure if I can do that without incident I will hunker down with service manual and start ironing out the rest of the problems.
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Re: Oberheim OB8 Repair & Calibration

Postby themilford » Wed Dec 04, 2013 1:06 am

Just dropped my OB8 off at the Analog Lab. It was becoming more and more obvious that I just wasn't gonna have time to stumble through a repair myself.

If all goes well with this repair job I am considering taking their 10 week Tech Mentoring program to sharpen my repair skills and broaden them to include synths and more complicated equipment.

I'll let you folks know how it all goes.
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Re: Oberheim OB8 Repair & Calibration

Postby themilford » Tue Jan 07, 2014 7:07 pm

just got the bill on my OB-8.

$1000!

Crazy.

Had a bad CEM, bad transistor, some caps, resistors and a few MUX chips replaced, replaced a bad balance pot… but YEESH. And I even supplied them with most of these parts!

It'll be nice to have her back and have a repair that has a bit of a warranty on it… but all future repairs will be done by myself. My New Year's resolution is to brush up on and continue my learning in electronics and repair. No more fear of delicate PCBs. Time to get acquainted with my 'Scope and go for it.
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Re: Oberheim OB8 Repair & Calibration

Postby themilford » Tue Jan 07, 2014 7:13 pm

FWIW: I only paid $1000 plus shipping for this thing with a flight case and it's in mint physical shape… so about $2200 total ain't bad I guess for a nice and freshly serviced OB-8. Right?

I'll report back next week when I pick her up.
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Re: Oberheim OB8 Repair & Calibration

Postby synthparts » Wed Jan 08, 2014 3:09 am

Did you not get an estimate for the repairs? All the chips are socketed in the OB-8 so replacing them is quick and easy. Actually more important than a scope is a multimeter, good temp-controlled soldering iron, and a vacuum pump desoldering station like a Hakko 808...
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Re: Oberheim OB8 Repair & Calibration

Postby themilford » Wed Jan 08, 2014 7:01 pm

synthparts wrote:Did you not get an estimate for the repairs? All the chips are socketed in the OB-8 so replacing them is quick and easy. Actually more important than a scope is a multimeter, good temp-controlled soldering iron, and a vacuum pump desoldering station like a Hakko 808...


Quote was between $600 & $900.

I hoped it would stay on the low side. I had sorta hit a wall with it and was unable to track down specific issues. swapping chips didn't seem to help at the time but it turned out the culprit was a number of things. The tech seems to think because of the plethora of varying issues is had that maybe it got hit with a voltage spike/surge at some point… which wiped out the transistor and CEMs (I had already replaced the two output 3360s and 3080s which repaired the dead output). It was not calibrating and voices were all over the place and front panel controls not responding.

I just figured for a synth this nice for a such a good price and with my schedule so filled up it was better to have the professionals go over it with a fine-tooth and skilled comb so I can start making music. ...And I was scared to start desoldering delicate traces and swapping out polystyrene caps and such.

I feel like anywhere else on the planet this repair would have been $500. I guess that's what I get for living in the Big Apple… as I said… this will be the last time I pay for a synth repair. At least now I can spend my free time making music instead of leaning how to use a scope staring at a broken splayed open OB.

Now I'm all in with a minty OB-8 for less than $2200.

We live, we learn.

Cheers,
D
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Re: Oberheim OB8 Repair & Calibration

Postby synthroom » Wed Jan 08, 2014 11:01 pm

It's a fine synth and the price is not out of the ball park.
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Re: Oberheim OB8 Repair & Calibration

Postby themilford » Sun Feb 09, 2014 3:53 pm

Got it home and everything seems to be working.

They have a 30 day warranty on the repair so I should put it through it's paces in the next few weeks and make sure it's solid.

This thing is pretty amazing… my head is spinning with the features… it's a huge box of bells and whistles over my Prophet 600. I'm reading the manual and the extra functions not obvious from the panel are crazy and plentiful.

So, is there anything I should check that may have gone untested or commonly overlooked in a repair?

Cheers,
D
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