80s synth RAM cartridge misery

ALAS · Joined: Oct 14, 2013 Posts: 11 Location: Philadelphia

New postPosted: Today, at 2:50 pm Post subject: 80s synth RAM cartridge misery Reply with quote Edit/Delete this post Delete this post Mark this post and the followings unread
Hi

I am hoping someone can give me a little bit of help with a RAM cartridge-related problem I am having.

I have a Siel DK-80 synth (analog para/poly with MIDI) from 1985 and have been struggling with it for months trying to turn it into "a synth a normal person can use." It only has 10 patch memories, and with its terrible interface, I'm always accidentally overwriting patches. It came with a RAM cartridge that was supposed to hold 50 more patch memories but it would never save the patches for more than a day or two even after I replaced the CR2032 cell battery in the cartridge. Eventually the cartridge seemed to stop working entirely and I gave up on it, but recently I decided to try to fix the cartridge again and ordered a NOS replacement RAM chip on ebay. I opened up the cartridge and replaced the chip, the sole electrolytic capacitor, and the battery once again for good measure. The only other components in there are a single resistor, a single ceramic disc capacitor and two diodes, which I assumed should be fine. For a few days, the newly-repaired cartridge seemed to work perfectly. I had all my patches for my live set in order on it and I built a footswitch to cycle through them and I thought, "This workflow is just as intuitive and convenient as any dang ableton live!" Then yesterday, I went up, turned the synth on, and the patches from the cartridge were gone again! I had recently finally gotten into the habit of Sysex-dumping all my patches to my computer for backup but in my newfound confidence with the cartridge I had not backed up any of the newer patches I had saved on there so they were gone for good. The cartridge now is saving new patches like nothing happened, so it is definitely not damaged.

I know that probably no one has this synth but does anyone else have any similar experience with RAM cartridge failures in 80s synths? I would be willing to start trying to fix things if I had any idea what the source of the problem could be. Dealing with memory and RAM I am totally out of my comfort zone. Because I overhauled the cartridge I am assuming it is not the cartridge that is the problem. The cartridge cannot be inserted when the synth is on or the synth may freak out and reset itself, erasing all its other patches as well, so I leave it in all the time. But I am guessing that whatever is going wrong is probably happening at power-on or power-off. Would the only thing that could be causing this be something that interrupts or interferes with the supply of voltage from the CR-2032 battery that normally keeps the RAM awake? Like if there was a brief excess of voltage in that part of the circuit at power on, could the presence of too much voltage at the RAM chip's supply pin also interrupt its operation?

Any other, better ideas? Now that I am thinking about it a little harder I feel like maybe I should take the cartridge apart again and see exactly what those other components do.

But really, any general ideas or advice from experience would be an enormous help.

Thanks
Alison

elmegil · Posted: Sat Oct 18, 2014 7:44 pm Post subject:

I'd at least try that ceramic cap.

ALAS · Joined: Oct 14, 2013 Posts: 11 Location: Philadelphia

I'm starting to realize that maybe discounting the diodes was a mistake. I'll take a look at the layout of the circuit on the cartridge again and see if they're there as protection between the rest of the synth and the cartridge. If they are broken down and allowing voltage to enter from the synth could that be erasing the RAM? I still don't know whether the presence of a bit too MUCH voltage can reset a RAM chip.

ALAS · Joined: Oct 14, 2013 Posts: 11 Location: Philadelphia

whoah! Last night when I went to play the synth the RAM cartridge had populated itself with crazy patches where all of the parameters were set to random values. But not every memory position on the cartridge had one. It can save 50 patches at positions 50 to 99, and I would say about 30 of those crazy patches were on there. And mixed in with all of those, about 5 patches I had made that I thought were lost had RETURNED!... and mixed in with those were about 5 patches that were my patch on one oscillator and random values for all parameters on the oscillator (the synth is bitimbric with two oscillators with all parameters set independently).

Now I really don't know what could be going on!

elmegil · Posted: Mon Oct 20, 2014 12:26 pm Post subject:

That still sounds like it could be related to the battery circuit. If you take the button battery out, what charge does it have on it relative to its nominal value? If you have something that's draining it too quickly, I could see low voltage (enough to keep part of the RAM active) doing this.