Memorymoog "DEAD OSC" on all voice cards OSC3

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1

Here’s hoping someone could help me pinpoint this…

Started having issues with my Memorymoog (non-plus) tuning voices, so I accepted that it was time to start some major overhaul on it. I did the following:

*Re-capped all the boards minus the pot boards (I really don’t want to remove those)
*Replaced the CEM sockets with machined-type on all voice cards and the one on the common analog board.
*Replaced the bus IC sockets on the digital board, analog board, voice cards.
*Performed the service bulletin pre-reqs and then did the auto-tune upgrade. Etched the buffer board from a file and burned my own eproms for the 2.4 software.
*Replaced the fan with a DC fan.
*Calibration up to the end of the voice cards.

I’m now having an issue where all voice cards OSC3 are coming back as “DEAD OSC” in the C7 routine. I was looking at the schematics and trying to understand the OSC3 summing circuit because I’m also seeing that on OSC3, the mixer volume is very low and only comes alive when KB TRACK 2/3 is switched on, and then the mixer volume just doesn’t work unless KB TRACK is turned back off.

I’m probing around on the common analog board, but man I’d be super grateful if anyone has ever run into similar on theirs and could shoot off some suggestions…

WLR

2

Hi Mike-

Now you’ve gone and done it - upsetting the memorymoog Gods, shame on you! :blush:

I’m suspicious that the other osc are really being updated. Maybe start by clearing out the auto tune values (press C5 iirc). When you hit C7 are you seeing the osc 1 and 2 values change? Maybe tweek a trimmer pot or 2 to verify they’re really being read.

If osc 1 and 2 are working as expected in the C7 routine have you tried tweaking one of the OSC 3 range trimmers to see if you can bring it out of dead osc? I’m not sure what the revised auto tune software does but maybe it skewed these values.

Its also possible there’s a timing issue, maybe on the DB affecting the timing signals such that they aren’t sampling osc 3.

3

Scratch what I wrote previously. If there’s a problem with the control signal for Osc 3 Amount it could affect the C7 read out. The firmware enables and sets each Osc amount to max (I believe) to ensure a proper read out.

The Osc Amount doesn’t come from the CA board. The CA board sums all of the mods and frequency components. Instead check the connection from the DMUX board to the voice cards. Also make sure the decoder output (U12, U27) is updating for Osc 3 amount

4

I could also be dealing with an issue in the ribbon cable for all I know. I hate how the cable is shared across all 6 voices; that’s so gross. I did replace all the ribbon connector sockets on the voice boards since they were on the bench anyway.

Thanks for clarifying the difference between what happens on the DMUX as opposed to the common analog board. Since I put the DMUx board back in with some components missing the first time due to my sheer stupidity, it also wouldn’t surprise me if I fried something out. I’ll keep posted. Thank you for the assistance!

5

Components just missing i.e. left off won’t fry anything.

6

Well, for what it’s worth I found a little something…

When I lift the ribbon connector off S12 on voice card 5, OSC 3 immediately gets louder (obviously a note is missing) and seems to go back into ‘range’ if that makes sense. So there is something going funky on that voice card maybe? Only happens when I lift S12 - if I life the S56 off the DMUX board and just briefly touch the contacts it gets louder too. Sure seems like a short or connection issue with something on Voice 5 bringing the rest of them down…

7

S56? Did you mean S54? S54 carries the 3 Osc amounts so I can see this affecting the Osc level/volume.

Word of caution- lifting those connectors while power is on and making contact is extremely risky. I strongly recommend you not do this.

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I did mean S54, sorry. And taking your advice; I realize they carry control voltages. I won’t lift them with the power on. I should probably check my soldering on that card since I did replace the socket. I will say, if for nothing else, I’m very good at soldering and have good tools but if I was capable of leaving out components on job, who knows what else I fell asleep at the wheel on…

EDIT: why does S54 have 3 different sockets all routing the same?

9

Excellent. You’ll figure this out, of that I’m certain.

Regarding the 3 parallel socket locations for S54 I can only guess that when they built the DMUX they had a different routing scheme in mind for those signals.

10

In theory, I should be able to completely disconnect all the voice cards on the ribbon cables and just connect 1 card, right? Just to isolate? I want to see if it’s the card or the actual connector on the ribbon just in that particular spot bringing everything else down…

11

I assume you mean removing S54. Yes that should tell you if the problem is at the signal source or if one of the VCs is pulling the Osc 3 amount down. Or maybe something else altogether. You can also defeat all but the one voice that’s still connected using C4.

12

Well I disconnected the entire ribbon assembly of S54 and S53 and removed all the cards. I labeled the cards and then did some tracing on VC E which is the one that was showing me different activity with the ribbon S12 was lifted off. Everything traces out fine from that socket and compared to another card. So I connected S54 and S53 to only 1 voice card and I get nothing. Unless something else is wrong, I would have assumed you could have a 1 voice Memorymoog if you only had 1 card installed?

13

Ah…I believe removing the cards is different than just removing those ribbon cables. Only I don’t recall what it is. There maybe something funny with the power distribution to the boards or routing the audio outputs back to the CA board.

Are you working with a scope?

14

Yeah…
Here are a couple videos to show what I’m dealing with.

https://www.youtube.com/watch?v=R_jZAdS30j4

https://www.youtube.com/watch?v=COWooH6rLtg

15

Oh man, I wish we started with those videos. I thought Osc 3 had no sound or very limited output. This is a Osc 3 pitch/ frequency issue which does point to a voltage input common to all VCs. Now we’re back to the CA board.

I would look at the OSC 3 Sum signal coming into any VC as you play a note.

16

I’m looking at the common analog. Here are the bullet points to the problem just so I don’t ramble:

-OSC3 low on all VCs; turning up OSC3 mixer section produces a squeal which leads into the note. Sometimes the OSC3 sounds like it’s dying a slow death. Autotune will read the hex data from OSC1 and 2 but all OSC3 show dead osc.
-OSC3 on the remaining cards will work if S12 is disconnected from Voice card #5. Mixer control will work, but autotune will not read any of the oscillators (all dhow dead osc)
-With S12 disconnected, OSC3 will sound at full volume if 2/3 KB TRACK is enabled, but mixer control will not work.
-Last night I replaced a bunch of 4017s and 4051 chips in the DMUX board for the hell of it which didn’t change or affect anything.

*Keep in mind I’ve done the autotune upgrade on this so I have changed things and re-routed connections per the instructions. I’m pretty sure the problem only surfaced after I did the upgrade, not when I re-capped it. But I’m not 100% on that, unfortunately. I did check every board back in the synth after re-capping but I was mainly looking for ‘is it broken or working’.

So Marky, you think this is at the common analog board? It’s so weird! It was suggested to me in a FB group to check the voltages at the S&H on the DMUX board and I scoped a bunch of places that all gave me exactly what the schematic showed.

17

Ok, I pulled out U13 3360 from voice card E instead of the ribbon and I get volume from the others. So I’m now thinking I have either a bad 3360 or something around it.

18

Trying to avoid some more misunderstandings so please clarify the following:


19

My luck keeps getting worse and I’m not rushing, so I’m not sure what I keep doing wrong here…

I’ll start with: “I don’t know when that blob of solder dropped on the traces”; it could have been earlier on, it could have been today when I was tinning a new ground wire. I just don’t know and don’t have any pictures to reference from before I pulled the board. At any rate, I removed that blob and my problem didn’t change so. But I did find it before putting the board back in at any rate, so I may have just avoided a huge catastrophe…

But I came to this when I was measuring voltages on the DMUX again earlier and found that at pin 10 of U3 (7417) which by the schematic looks to go back toward the OSC3 amount, I was reading 5v with a drop anytime keys were played, and it’s supposed to read 15v. I realized that the 7417 was in that spot right next to the huge gob of solder for the ground wire, so I decided to pull the board and clean that up, replace the socket and chip and see where I’m left off. After I did this, I noticed the blob of solder I dropped. So, it may have been when I was tinning the ground. Either way that didn’t change anything and I replaced the surrounding 7417s just to be sure I didn’t short anything… no change.

To answer the questions:
I assume you mean low output level?. Yes, with S12 connector connected on Voice5, all OSC3s are extremely low. Pressing KB TRACK 2/3 brings the volume back to life but mixer control does not work.

I assume you mean the C7 routine. Autotune is a separate routine that reads those values and provide correction voltages. I’m guessing running the actual autotune shows “ 0 tuned” when complete? Yes, sorry, when I run C7 and check the hex data for each voice/osc, if S12 is disconnected from Voice 5, all oscillators will read DEAD OSC. If I plug in S12 on Voice 5, and run C7 on any given voice/osc, it will read the hex data on OSC1 and OSC2 but all OSC3s will show DEAD OSC.

Check your +15V and -7.5V with S12 connected and disconnected I did and it didn’t seem to make any difference. Everywhere so far I’ve checked on the DMUX is giving me good, correct voltages.

As a test I plugged in 2 extension sockets to voices 5 and 6 so I could get my scope on it. I tested the good voice card, voice 6, on pin 3 of S12 which is the 2/3 KB TRACK. When S12 is disconnected from Voice 5, pin 3 on S12 voice card 6 is high, 10v. When S12 is connected, pin 3 shows no activity on the scope and reads about 1.2V, and will only go high when I physically turn on 2/3 KB TRACK.

That’s where I’m at currently…

20

My blobs will put your’s to shame. Good you spotted it but I wouldn’t worry about it anymore-shit happens.