Memorymoog reset

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DiscoE
Posts: 12
Joined: Wed Nov 27, 2019 2:02 pm

Memorymoog reset

Post by DiscoE » Thu Apr 02, 2020 3:06 pm

Hello,
I have a Memorymoog+ and it is currently frozen on boot up and reads 88 on the readout. No controls or buttons work except the octave change. I have read that a CPU reset can be done or shorting the p49 pin. I have tried these to no luck. I am not a tech but I have some knowledge of opening and tinkering. I watched a video where the tech reset the CPU on a Prophet 5 which has the same Z80 cpu by connecting the test (p49 pin) to the 5v rail. I havent tried this yet but could be an option. Maybe if someone has any info or a better description of either of these processes I would greatly appreciate it.
Thank you
Ian

alainhubert
Posts: 83
Joined: Sun Feb 01, 2009 10:39 pm
Location: Montreal, Quebec, Canada

Re: Memorymoog reset

Post by alainhubert » Thu Apr 02, 2020 4:39 pm

If the synth freezes up upon power-up, I doubt very much that simply forcing a CPU reset would resolve the issue.

It's more likely that the CPU might have gone bad (it happens often with old Z80), or that some of the RAM chips, or logic gates might be failing.
I would try to find a reputable tech that could have a look at it. Synthchaser.com, or Synthpro Restorations come to mind, both of which have numerous videos on YT that show their great repair work. Because if it's the power rails that are unstable, or the RAM chips that are failing, or anything else, a professional tech is better equipped and has the necessary knowledge to fix everything.

Best of luck to you, and stay safe!

DiscoE
Posts: 12
Joined: Wed Nov 27, 2019 2:02 pm

Re: Memorymoog reset

Post by DiscoE » Thu Apr 02, 2020 4:57 pm

Thank you for your reply,
I actually have another memory moog for parts and I could swap the z80 from there.
Is there a place to get replacement z80s specifically for synths (memorymoog).
If I can do it my self that would be a lot better. As its hard right now to be getting synths to be serviced at this time. If you have any other advice I would love to hear it.
Thank you
-Ian

alainhubert
Posts: 83
Joined: Sun Feb 01, 2009 10:39 pm
Location: Montreal, Quebec, Canada

Re: Memorymoog reset

Post by alainhubert » Thu Apr 02, 2020 5:10 pm

Yes, if both CPUs are on a socket you could try swapping them and see. But realize that many times, peripheral chips might also fail. Logic gates, address decoders, memory chips, and not simply the CPU itself.

The Memorymoog is especially susceptible to failures, because of its very complex nature, and also very often failing PSU (overheating, bad electrolytic caps, etc).

If you have access to a multimeter and an oscilloscope and know a little about how to use them, you could check the different power rails to make sure that they output the right DC voltages, and that they are clean.

I know that this virus thing makes for difficult times when trying to get things done, especially having a classic synth fixed by someone in another state. But that's unfortunately one bad side of owning classic vintage analog gear: they all will fail at some point in time due to their age. Much like us...lol!

Hope this helps a little.

Alain.

Markyboard
Posts: 326
Joined: Wed Jul 30, 2003 6:46 pm
Location: Springfield, VA

Re: Memorymoog reset

Post by Markyboard » Fri Apr 03, 2020 11:29 am

I agree with checking the power rails first. Really the only ones that come into play here are the +5V and the +5V Raw.

Before swapping chips which is really guess work (but understandable) I would re-seat both ends of the 40 pin ribbon cable going from the Digital Board to the Sequencer board.

DiscoE
Posts: 12
Joined: Wed Nov 27, 2019 2:02 pm

Re: Memorymoog reset

Post by DiscoE » Tue Apr 07, 2020 3:38 pm

Tried both CPUs and Reseating the 40 pin ribbon. Is there a way to test the ram chips?
This is from the service manual:

NOTE: If all VOICES are defeated
accidentally, the unit may be RESET by
shorting the central pin to an outside
pin of the MANUAL RESET CONNECTOR P49
on the DIGITAL BOARD.

is there any tests that I can perform?
Thank you

alainhubert
Posts: 83
Joined: Sun Feb 01, 2009 10:39 pm
Location: Montreal, Quebec, Canada

Re: Memorymoog reset

Post by alainhubert » Wed Apr 08, 2020 12:52 am

Concerning testing RAM chips, a quick and easy way is to check for hotter than normal chip casings when the power in on for a few minutes. It's not infallible, but many times a defective chip will tend to overheat. But not always.

Another way is to, again, swap them for known good ones.
But since the synth locks-up upon power-up and nothing works, it's rather difficult to pinpoint the source of the problem.

Also, there are many, many wire ribbons and connectors inside this thing, any one of them could cause a bad contact, or have a broken wire (often near the connectors). It could even be a cold solder joint somewhere, or cracked one, who knows?
It could also be the lithium battery (for RAM memory backup) that could have leaked onto the PCB...

As for resetting deactivated voices, I don't think that would even work since the CPU seems to lock-up as soon as the power is on...

This video might be helpful perhaps?
https://www.youtube.com/watch?v=7jzbUAmY6xY

Markyboard
Posts: 326
Joined: Wed Jul 30, 2003 6:46 pm
Location: Springfield, VA

Re: Memorymoog reset

Post by Markyboard » Wed Apr 08, 2020 6:35 am

And the 5V supply is good?

Markyboard
Posts: 326
Joined: Wed Jul 30, 2003 6:46 pm
Location: Springfield, VA

Re: Memorymoog reset

Post by Markyboard » Wed Apr 08, 2020 7:19 am

alainhubert wrote: Wed Apr 08, 2020 12:52 am
This video might be helpful perhaps?
https://www.youtube.com/watch?v=7jzbUAmY6xY
OMG, an entire troubleshooting video for what turned out to be a bad external cable? Oh well, guess I'm not alone in those type of bonehead mistakes. And of course the video is well done by SC as usual and is helpful from a troubleshooting approach perspective. Especially if you watch it in reverse :mrgreen:

The other thing I forgot is how unbelievably messy the inside of a MM is . I would never want to work on someone else's unit.
Image

DiscoE
Posts: 12
Joined: Wed Nov 27, 2019 2:02 pm

Re: Memorymoog reset

Post by DiscoE » Fri Apr 10, 2020 12:26 pm

Awesome Ill check those out,
Did you replace the power and fan? Those are good moves. Might be my next frontier. Let me know if anyother ideas come to mind. I appreciate all the input. Nows the time to fix all your broken gear and I have a lot!
-Ian

Markyboard
Posts: 326
Joined: Wed Jul 30, 2003 6:46 pm
Location: Springfield, VA

Re: Memorymoog reset

Post by Markyboard » Fri Apr 10, 2020 1:42 pm

DiscoE wrote: Fri Apr 10, 2020 12:26 pm Awesome Ill check those out,
Did you replace the power and fan?
Yes- a few years ago. This power supply requires no fan. But another thing well worth doing is cleaning up the internal harnessing/cabling so that you can flip up all the boards with minimum fuss. Some of them can be shortened; some need to be extended. The original ribbon cables were a mess folding them underneath. This can be easily improved if you build news ones to the proper length.

Reminds me, in the Synthchaser video there's a large transformer (I believe) on the right side of the unit. I wonder if that's a replacement audio output transformer?

Markyboard
Posts: 326
Joined: Wed Jul 30, 2003 6:46 pm
Location: Springfield, VA

Re: Memorymoog reset

Post by Markyboard » Mon Apr 13, 2020 6:15 am

Hi DiscoE (if you're still monitoring)

I thought of one more thing this morning. A fairly short while back a forum member had a similar problem as I recall. Now don't ask me why this works or the theory behind it but apparently if you wrap your EPROMS in aluminum foil for 24 hours (iirc) it does something to them (maybe discharges any parasitic capacitance?).

Anyway this was effective for him and you may want to give this a try. You can Google this as well. One of our well respected EEs here (The Real MC) also confirmed this as being a valid procedure to attempt. Just be certain to take necessary precautions not to zap your devices with ESD.

alainhubert
Posts: 83
Joined: Sun Feb 01, 2009 10:39 pm
Location: Montreal, Quebec, Canada

Re: Memorymoog reset

Post by alainhubert » Mon Apr 13, 2020 2:20 pm

I don't know about wrapping EEPROMs in aluminium foil, but a few years ago I was working on another synth (replacing keyboard felt strip on a Korg DW8000) and had the synth locking up on me for no apparent reason. I discovered that the ambient light shining on the EPROM chips was strong enough to make the synth crash, even though there was a white piece of tape over the chip window. After putting an opaque black piece of electrical tape on top, everything went back to normal.

DiscoE
Posts: 12
Joined: Wed Nov 27, 2019 2:02 pm

Re: Memorymoog reset

Post by DiscoE » Mon Apr 13, 2020 2:37 pm

Awesome I will try these tips.
You just wrap all the eproms in aluminum foil? or are there specific ones to concentrate on?
Thanks for all the responses. Hopefully I can get this baby back to life.

Markyboard
Posts: 326
Joined: Wed Jul 30, 2003 6:46 pm
Location: Springfield, VA

Re: Memorymoog reset

Post by Markyboard » Mon Apr 13, 2020 3:02 pm

I'll see if I can find that post and provide a link. But I don't think there was any detail. I would try them all. I was skeptical as I like to know why things work or don't. Never did get a plausible answer but it's hard to argue with success especially when there's multiple reports of such.

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