More on Memorymoog tuning

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Technician Larry
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More on Memorymoog tuning

Post by Technician Larry » Wed Oct 19, 2011 5:58 pm

Carl Solovox's Memorymoog came back for tuning problems again. Some depressing reports about this problem are circulating on the net. You have to replace all the sockets and connectors with updated gold plated parts - THEN it can stay in tune. I did find some flaky connections in the wiring harness, but those tended to clean up reliably with some Deoxit. What did not check out was the 36 trim pots... for VCO scale and range calibration. After 30 years of service, the contact resistance of the wiper to the element in many of these trim pots was becoming significant and drifty. I observed that intermittent resistance from these trimmers was the cause of the auto tune failures. Some techs report that you can remove these, rotate them 180 degrees - reinstall and recalibrate. The new contact point of the wiper on the element will be reliable. It is a lot of work to remove, replace and recalibrate 36 trimmers and I recommend that new parts be installed while in the process. Bourns still makes the 3299 series pots used on these voice cards and Mouser Electronics has them in stock at a fair price.

I finished the trim pot upgrade last night and so far the results are quite pleasing. See the full report here:

https://www.facebook.com/photo.php?fbid ... 525&type=3

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MC
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Re: More on Memorymoog tuning

Post by MC » Wed Oct 19, 2011 11:59 pm

Make sure you replace the battery, even if it isn't leaking. Mine went kaput this year, just short of thirty year life.

I originated the gold plated replacement connector methodology. Did it to my MM. Lots of work but the tuning reliability improvement is **SO** worth it. Deoxit doesn't always work because it doesn't prevent the tin plating on the original connectors from corroding.

You don't have to replace all the connectors - just selected ones. See my MM page below:

http://www.retrosynth.com/~analoguedieh ... index.html
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RL
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Re: More on Memorymoog tuning

Post by RL » Thu Oct 20, 2011 3:15 am

When you do not fix the tuning software of the Memorymoog you will never get a stable tuning for a long time.
Sorry, but this is the reality :(

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Kevin Lightner
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Re: More on Memorymoog tuning

Post by Kevin Lightner » Thu Oct 20, 2011 5:19 am

I agree with everyone here so far.

Gold plated connectors, new trims, improved Linhard software, new battery.
But that's the whole problem now.
Years ago, one could fix just one problem and send a client on their way.

Now one can't always go into a synth and do just one operation.
They may have to desolder hundreds of connections and replace many parts all during the same job.
The process of removing boards to fix one thing can cause problems elsewhere too and so many things must be done all at once.

Fwiw, Oberheim updated their OBX-A autotune software many, many times.
Autotuning can be very tricky to do well.
It requires both hardware and software engineers to work closely together.

I also believe that the Memorymoog IC sockets are poor.
They are the cheaper leaf types and can corrode and lose friction over the years.
Repeated chip replacements can wear away their plating too.
I don't agree on using sockets at all unless they're high quality machined types or for custom chips.
I tend to solder most chips directly to a board unless there's some good reason not to.
But doing this on a MM would take a LOT of work.

I had one client who sent RL his MM for service.
It came back fine except for one voice.
A VCO chip had moved in its socket during shipping from Germany to the US.
I found it within a minute with the client watching, but we were lucky. I knew where to look and what to look for.
This small problem could have become a much larger nightmare had Rudi not first serviced it too.
I wouldn't haven't even allowed here at all had Rudi not been the previous tech and that it was to be hand delivered, not shipped.
But this suggests that rough shipping and poor sockets may necessitate even more work required for MM's, especially ones intended for shipping.

I quit servicing MemoryMoogs completely now.
Same for Polymoogs, CS80s and some other synths.
Better to be king for a night than schmuck for a lifetime. - R. Pupkin

torinkrell
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Re: More on Memorymoog tuning

Post by torinkrell » Sun Nov 13, 2011 12:39 pm

I understand that the Memorymoog offers one of the biggest challenges in synth maintenance today. What other synths are similarly challenging to repair and keep running? Which use failure prone rare parts, and which use parts that will be easy to find even in the future? Which vintage analog synths are relatively easy to repair, or rather reliable - and can be expected to stay that way as they age further?
I would guess that (looking through my gear) a Minimoog D, Roland Juno 60 and a Yamaha CS-5 would be examples of the latter.
Akai AX-80
Korg Polysix
Roland Juno 60
Moog The Source
Yamaha e1010 BBD
Moog Parametric EQ
Sequential Prophet Pro~One
Altec AS-1600 audio oscillator (1947)
Moog Music Minimoog Model D (1973)

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MC
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Re: More on Memorymoog tuning

Post by MC » Mon Nov 14, 2011 12:59 pm

Wow, so many questions
torinkrell wrote:I understand that the Memorymoog offers one of the biggest challenges in synth maintenance today.
While citing the Memorymoog, any analog polyphonic or analog with digital patch storage is a challenge as they are complex machines.
What other synths are similarly challenging to repair and keep running?
Repair-wise I'd say the worse ones are those with point-to-point "spaghetti" wiring such as the old Yamaha CS-80/60/50. Everybody has varying experiences on which vintage gear is easier to keep running, there doesn't seem to be a solid consensus.
Which use failure prone rare parts
Failure prone are those with early generation tantalum caps before 1982 (not every synth used them). Sometimes poor design can contribute to part failure downstream - I was never impressed by power supplies in ARPs, and SCI pushed their power supply current capacity too close to the maximum in their P5s.

Frankly every vintage synth has some rare parts in the form of switches, pots, ICs. I am not fond of anything with slidepots as they can be difficult to find in low quantities 20 years down the road and finding an exact physical fit can be a real problem (mm travel, footprint, etc). Board-mounted pots and switches pose a challenge - I have a Barbetta keyboard amp with bad pots and replacements that fit the PC board holes are nowhere to be found, had to shoehorn trimpots in place of them.
and which use parts that will be easy to find even in the future?
Don't count on EVERY part being easy to find in the future. Through-hole components are getting harder to find as OEMs are switching over to SMT. Stuff like the CEM3340 VCO ICs are not bloody likely to be made again because the original fabrication technology is obsolete and the development costs of converting the substrate design to modern fab lines would never be recovered in such a niche market. Many people buy a dead or dying synth to scavenge for spare parts. Technology proggresses and obsolescence is a part of it, fact of life.

Some stuff like the Pro-One and ARP Quadra use a microprocessor with the OS stored on the on-board EPROM. You can't retrieve the ROM contents off these ICs. The source code was written in 1982 and no longer exists. This part can't be duplicated. Lose the microprocessor and you have a doorstop.
Which vintage analog synths are relatively easy to repair
Generally any monophonic analog with no digital patch recall
or rather reliable and can be expected to stay that way as they age further?
That is a function of how well it was cared for by former owners and/or how well it was designed. Obviously storing a synth in a damp basement or garage is not good for certain components like switches and pots. And while an Oberheim OB-X is a great sounding synth that is easy to service, the DAC circuitry has a design error that will blow the CMOS ICs under certain conditions.
I would guess that (looking through my gear) a Minimoog D, Roland Juno 60 and a Yamaha CS-5 would be examples of the latter.
Those are a good start. But don't be so paranoid over reliability of vintage gear. In the right hands they can last a long time. Proper storage and operation go a long way to reliability. Of course there are risks with buying used vintage gear because you don't know how well they were taken care of. That's the price of admission for the vintage analog club and you have to be prepared for some repair or restoration costs.
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