My Self-Indulgent Memorymoog Refurb Thread!!! (Long Post)

[Markyboard]

It's up to a bargain price of $8900.00.

Last chance - get your bids in. They don't make em like this any more (thank God). Don't wait - you'll regret it in the morning.

[ProfD]

OK- I'll throw out an almost random date of Sat, June 25 around noon. We can get the grill going and do the afternoon hang. Feel free to throw out another date if this doesn't work. Maybe best to start another thread but since you asked here...

I'm good with June 25th. Let me know if the hang materializes.

[eric]

I can probably swing 6/25, pending family calendar confirmation. I'll be up in that general vicinity for the Sting/Peter Gabriel show on 6/23.

[goldenanalog]

Hello! My first post! As a MM aficionado, I wanted to address others who share my love for these unwieldy beasts with a question:

 

I'm toying with the idea of using external active cooling on my MM - I wonder if there would be any value in mounting a liquid cooling system on the heat sink, or building a platform with internal liquid cooling that physically contacts the bottom of the MM's chassis - thoughts?

[Markyboard]

Welcome to the forum goldenanalog! Thermal engineers (I'm strictly a EE) do a lot of analysis to determine effectiveness of the cooling devices to be used; fans, heat syncs, liquid coolers etc. IMO Sticking a liquid cooler inside the Memorymoog looks to be a lot of guesswork and effort that may not yield any effective results. Also I've read that liquid coolers produce a type of "gurgling" / pumping noise. This has dissuaded me from using them in my home built PCs and I opted for silent fans instead.

 

IMO you are far better off replacing the Power Supply which will eliminate much of the heat. I'm assuming you have not done this yet.

[vonnor]

June 25th probably OK for me too.

[Markyboard]

[Doerfler]

I'll be somewhere far away on that day, but I'll be hanging out with Mark on Father's Day (June 19th) at "The Hamilton" seeing Joey D. Maybe some of you cats can join us. BTW, how did this end on on the Memorymoog thread?

[goldenanalog]

Thanks, Mark!

 

My MM recently went through a rebuild under the brilliant care of Jareth Lackey (Synthpro) - I believe that the MM PS was slightly modified, but is still original -

 

What I'm thinking about is mounting a liquid cooling system onto the back of the MM itself - perhaps a liquid-carrying copper-pipe 'radiator' of sorts mounted to the heat sink; hopefully requiring no internal modification(s) to the MM. This is assuming that the heat sink is already ideally placed to dissipate heat; so my idea essentially would be to assist in cooling what's already there.

 

The platform idea would be similar, just cooling a larger surface area (the bottom of the MM)

 

 

[Markyboard]

As I indicated I'm no thermal expert nor do I have experience with modifying the thermal control on my Memorymoog. I wouldn't be able to advise you but would be most interested in what you discover should you pursue your plan. Actually it doesn't sound like what you're proposing would hurt anything and could only make it better. Good luck and keep us posted.

[The Real MC]

Zombie thread resurrection alert

 

Some years ago I landed a broken MM from a fellow musician. No audio, embedded system locks up, can't store patches.

 

A studio owner wanted a vintage polysynth for his arsenal. He's a guitar player and knows nothing about synths. He landed a broken Oberheim FVS for nothing from one of his fellow musicians. He took this FVS to a tech we both know; this tech was unable to comprehend a complex polysynth of this scale, so he recommended me.

 

I managed to fix a busted power supply rail, which got audio out of the thing and permitted a repair list. Being a guitar player, it was far more than he wanted to spend. So he offered to trade for one of my vintage polysynths (I offered the DSI OB6 but he wanted vintage). I offered this surplus MM, as it would be a much easier system for a novice player to use than the FVS. All I had to do was restore the MM.

 

So for two years I've been resurrecting this MM with a lot of starts and stops (I don't normally take this long but have been very busy with elder care with both my parents). I'm not only doing the makeover described on my infamous webpage, but I'm doing a full recap, replacing CMOS ICs, and replacing old 1458/4558 opamps with TL072s and LF353s.

 

The worst job was the DMUX board. Almost a hundred new caps on that board.

 

One foible not listed on my webpage: a major source of problems is the cable assembly connecting to the power supply. The cable is soldered to the DMUX board, but on this unit the solder job was POOR. Unfortunately this requires almost a complete disassembly to get to, but cleaning up these solder junctions goes a LONG way to better reliability. I also found the same foibles with the ground wires.

 

Markyboard, I have not forgotten your request on that raw +5 rail. Coming soon.

 

Recently I ran into a logjam as the embedded system would display "* M O O G *" on the display, then freeze. I have the diagnostic tools to debug embedded systems (how many techs own a logic analyzer?) but I was not looking forward to that job on this rats nest. Then I noticed the orientation on the big 40 pin ribbon cable that connects the digital board to the sequencer board was incorrect... and the embedded system now runs!

 

It's all downhill from here... restore common analog, glide/EG, and voice boards and the Oberheim FVS is mine. Including the Oberheim digital sequencer and Anvil cases

 

I look forward to restoring that FVS.

[Markyboard]

Excellent - It's so nice to read about someone else doing this :cofee:

 

Iirc I bought a set of caps for the DMUX but ended up not installing them when the autotune issue turned out to be a bad -7.5 V supply. Still that's quite an undertaking, one I don't envy. I've also had my share of issues with that 40 pin ribbon. Never reversed it but any bad contacts will do some funky stuff. At some point I ended up making a new ribbon cable. All these issues just seem to blend into one continuous cloud of frustration, but mine continues to work well.

 

Thanks for remembering my +5V "Raw" current draw request. Can't remember how I posed the question but if you'd be so kind please light up all the LEDs and the character display when you measure it for a worst case loading. Coincidentally there was a post on GS just yesterday from the guy who is/was? the liaison for Heinz with the replacement power supply. According to him Heinz is no longer building these. Not sure that's quite true as I've asked him to build me a spare and plan to visit with him just outside of Dusseldorf end of October.

 

Good luck with your refurb Michael- will be very interested in your progress.

[The Real MC]

With an extensive restoration there is a lot of verification involved. Power rails are the first ones. I have to verify all the DMUX CVs and logic signals are working, then I can bury that DMUX board. I don't intend to untangle that rats nest of ribbon cables and wiring harnesses again.

 

Documenting the work as I go along, as I have a feeling this may not be the last MM that I restore.

 

When this is done, I'm going to experiment with some improvements on my personal MM - improved reset circuit using the TL77xx voltage rail supervisor, subboard under the keyboard with all range/scale/high end trimpots from all voice cards (no more reading upside down reverse characters from the display), voice gate LEDs (very useful on my OBSX, esp over MIDI).

 

I even scavenged the AT strip from the Panasonic keybed of a Korg DS8 and may shoehorn it into the MM... stay tuned.

[The Real MC]

Slight road bump with malfunctioning logic latches - the control signals for waveform select, LFO destinations, Voice Mods, etc. There be (8) CMOS 40174s (U54-U61 on DMUX board) that aren't latching.

 

There's a LOT of logic between the CPU and the latches...

 

Had to lay out a troubleshooting approach using my logic analyzer. Verified that the CPU circuitry is working, and the latch clock signals are present. Took a few tries to figure out how to get a decent trigger on my scope so I can view a non-repetitive 500 nanosecond latch pulse reliably (tricky stuff). The LA was a big help on that - man I love these old Tektronix modular 7xxx scopes!

 

Eventually found that the bipolar +/-7.5v data buss for these 40174s were stuck high. I can see the buffered data buss changing, but not the bipolar buss. So I yanked ALL (8) of the 40174s, and finally the bipolar buss was moving.

 

Plug one 40174 back in at a time until the buss stopped working again... found (2) 40174s that were defective... and they are the infamous early 80s RCA parts that have a history of going bad. Fortunately I had a stash of Fairchild 40174s in my surplus. Three of the remaining (6) 40174s were also RCA, even though those did work I replaced THOSE as they are likely to follow the failed ones.

 

...and my latches are now switching!

 

That was a heavy debug session. Tomorrow I move towards verifying ALL the logic signals from the DMUX boards (already confirmed CV signals are working), then I can bury the DMUX board and move to the rest of them.

 

Those bad latches explained why there was never any audio out of this thing.

[Markyboard]

Oh man, nightmare of nightmares! When I was troubleshooting my autotune problem and before discovering a bad -7.5V supply I also scoped out those timing signals - with a cheapo Owens scope. I don't own a logic analyzer unfortunately (it was one of my favorite tools back in my early work years). I did manage to trigger the scope but it wasn't easy to see those tiny pulses.

 

Congrats on getting past that one. Yup - you're deep into the Memorymoog bowels now my friend

[The Real MC]

Had a lot of trouble getting the scope to trigger at all. Turns out that the clock pulse at the 40174 was too distorted for the horizontal trigger - I had to trigger off a clearer TTL pulse upstream. Wouldn't had found that without the LA.

 

25 years ago, three of the large employers in the area were dumping their old test equipment and they showed up at this surplus store.

 

I grabbed a bunch of Tektronix stuff for peanuts, all 100% functional. 7834 scope chassis (which had been replaced with a 7904 when unobtanium power supply crapped out), (2) 7A26 vertical modules, 7B53A horizontal module, 7B92 horizontal module, 7D01 logic analyzer with probes, 7D02 formatter (converts 7D01 logic timing diagram to hex or octal or binary, memory for testing retention problems, etc), 7D15 universal counter (has a frequency counter function for VCO calibration). Later I picked up a 7L5 spectrum analyzer at a hamfest.

 

This was stuff I worked with during my day job, real sweet setup for music gear. The LA is rudimentary with only 16 bit channels (one of the early ones); but it's enough for 8 bit embedded systems for most analog polysynths, and one of its powerful features is I can have both LA and analog scope modules plugged in the chassis and trigger the analog scope system off the LA when its word recognizer conditions is met. Crucial tool for troubleshooting multiplexed analog and logic signals.

[Markyboard]

Oh yeah?

 

Well my tools are way better:

 

http://i1062.photobucket.com/albums/t490/Markyboard/IMG_3579_zps2mj1vzi8.jpg

 

[johnchop]

This is all Greek -- no, Linear A -- to me.

 

But in reading this, it's a wonder that any of these synths worked, like, ever. The number of single points of failure is staggering.

[Karl Schmeer]

Plug one 40174 back in at a time until the buss stopped working again... found (2) 40174s that were defective... and they are the infamous early 80s RCA parts that have a history of going bad. Fortunately I had a stash of Fairchild 40174s in my surplus. Three of the remaining (6) 40174s were also RCA, even though those did work I replaced THOSE as they are likely to follow the failed ones.

 

Over the years I have personally replaced many defective RCA chips.

You would think the inventers of CMOS integrated circuits (RCA)

would have made better chips, but no. It was a good idea to replace them all.

 

 

 

[The Real MC]

Plug one 40174 back in at a time until the buss stopped working again... found (2) 40174s that were defective... and they are the infamous early 80s RCA parts that have a history of going bad. Fortunately I had a stash of Fairchild 40174s in my surplus. Three of the remaining (6) 40174s were also RCA, even though those did work I replaced THOSE as they are likely to follow the failed ones.

 

Over the years I have personally replaced many defective RCA chips.

You would think the inventers of CMOS integrated circuits (RCA)

would have made better chips, but no. It was a good idea to replace them all.

 

When the MM is done, next restore project is the Oberheim FVS, Digital Sequencer, and cassette interface box - all loaded with RCA CMOS (some Motorola). I had already replaced RCA CMOS in my OBX and OBSX.

 

I remember opening the hood on my ARP 16 voice piano (made in 1981) and seeing piles of RCA ICs - CMOS and opamps. Small wonder ARP had warranty issues. That was an intensive restore job.

 

RCA didn't have the best foundry (SSS gets the award for the worst foundry), and the 1st generation RCA CMOS (1970s to mid 80s) lacked overvoltage protection on the inputs - now standard on today's CMOS.

 

I don't remember any Motorola or Fairchild CMOS from that era that failed.

 

Had bad luck with RCA CMOS opamps too. Their opamps with bipolar inputs like 4558 were not much better.

 

RCA had one part that redeemed them - CA3080.

[The Real MC]

Oh yeah?

 

Well my tools are way better:

 

http://i1062.photobucket.com/albums/t490/Markyboard/IMG_3579_zps2mj1vzi8.jpg

 

 

I see you paid the PB ransom

 

That is a very good tool. We use them for measuring tall tales...

[The Real MC]

http://www.retrosynth.com/~analoguediehard/studio/keyboards/moog_memorymoog/memorymoog-troubleshooting.jpg

[Karl Schmeer]

RCA had one part that redeemed them - CA3080.

 

Yah your right. I think they actually designed that one themselves.

You probably already know this but those CA/NS 13700 VCA chips

are the exact same die with a large boost transistor added to it. ( and larger package) It was used to train a new chip layout designer. So they took the old CA3080 layout and gave it to her and said "add a transistor to this". Almost as old as a 555 and still selling.

 

I love these restoration threads of synths from the 60s, 70s, and especially the hybrids of the 80s. So many electronic concepts working together. They are excellent teaching examples.

 

Please keep doing this.

 

 

 

[The Real MC]

RCA had one part that redeemed them - CA3080.

 

Yah your right. I think they actually designed that one themselves.

You probably already know this but those CA/NS 13700 VCA chips

are the exact same die with a large boost transistor added to it. ( and larger package) It was used to train a new chip layout designer. So they took the old CA3080 layout and gave it to her and said "add a transistor to this". Almost as old as a 555 and still selling.

 

I did read that story. 13700 also adds linearizing diodes on the input pins. Fortunately the additions could be isolated and the 13700 functionally was the same as 3080.

[The Real MC]

All output signals - CV and logic - check out on DMUX. Ready to bury that bastard board and move on to Common Analog which is getting new trimpots.

 

Markyboard, here's how I set up reading the current for the raw +5v rail:

 

1) Place MM in "Light Show" mode C-0-Enter

2) press "C" key, light show stops, all LEDs on front panel turned on

3) press "C" then enter to change to Sequencer mode, display reads SEQUENCER

4) All LEDs on, most segments in display are on

5) ammeter reading = 1.008A (!!!)

6) with "Light Show" active, current draw is dynamic - ammeter reads as high as 1.080A

 

Higher than the service manual reports!!!

[Doerfler]

Well my tools are way better:

http://i1062.photobucket.com/albums/t490/Markyboard/IMG_3579_zps2mj1vzi8.jpg

 

I had already forgotten about this, Mark. Glad you are finding it useful.

[Markyboard]

Markyboard, here's how I set up reading the current for the raw +5v rail:

 

1) Place MM in "Light Show" mode C-0-Enter

2) press "C" key, light show stops, all LEDs on front panel turned on

3) press "C" then enter to change to Sequencer mode, display reads SEQUENCER

4) All LEDs on, most segments in display are on

5) ammeter reading = 1.008A (!!!)

6) with "Light Show" active, current draw is dynamic - ammeter reads as high as 1.080A

 

Higher than the service manual reports!!!

 

Yeah, I was seeing similar results although I never knew that trick of pressing C following the light show to light all LEDs at once . This even yields illegal combinations like all LFO waveforms lit at once. Yup - that's a lot of juice. However 800 mA from Heinz' little add-on module should be more than sufficient for normal operations.

 

I very much appreciate you taking the time to check/confirm my observations. Btw I too will eventually change out the pots on my CA board- something I never got around to doing since performance continues to look good. Did you end up changing out the caps on the DMUX board?

 

 

[Markyboard]

Well my tools are way better:

http://i1062.photobucket.com/albums/t490/Markyboard/IMG_3579_zps2mj1vzi8.jpg

 

I had already forgotten about this, Mark. Glad you are finding it useful.

 

Yes - thanks for this most musical tool Dave - I use it in every measure.

 

 

[vonnor]

I actually felt a twinge of stomach pain when I read that.

 

Well done, sir.

 

~ vonnor

[The Real MC]

Did you end up changing out the caps on the DMUX board?

 

Yes I did. Those white polyester caps have a limited age. That was a big job but seeing this is an early unit from 1982 and the caps are 30+ years old then it was justified, especially for critical CVs. I will eventually do that to my own unit.