Crumar DS2 repair questions.

[Fetaldreamcore]

Hello.

I have a crumar ds2 here that I’m restoring. Appears to have seen moisture a bit from a basement. Rust and oxidation etc.

Question 1. These white plastic potentiometers - Are they available or what have people used as replacements. I have a seized one for the octave poly switch at the left of the keys. In fact all three of those controls were stuck. Managed to free the pitchbend but the 2k5 linear pot and this white 12 pin pot just won’t give.

Schematics:

https://www.synthxl.com/wp-content/uplo ... matics.pdf


Also what pin do the red/yellow wires attach to on that same white octave poly pot. These schematics are rough.

[Fetaldreamcore]

https://www.digikey.com/en/products/det ... =350473304

https://www.digikey.com/en/products/det ... =350473451

Will these work you think?

[guest]

as long as the physical dimensions match, any new pot and switch should work. as for the switch, how many positions is it? looking at the schematics it seems like all the switches are 3 postion. you can usually tell this from the panel graphic.

[Fetaldreamcore]

Yes either 2 or three. Looks like that brand of pot failed in the DS2 elsewhere. I can move them with vise grips. Ugh
so I’ll need two @ 2k5 linear and one @ 5k0 Lin. The switch I think I managed to get working.

Currently trouble shooting osc issues. Osc 1 has a constant note and doesn’t track pitch on the keyboard regardless of the key played. Osc 2 produces no sound. Switched their cards and same issue except osc1 pitch drifts slowly with #2 in its slot. I pulled all the chips and cleaned and sprayed em. No luck. Gonna keep pulling cards and cleaning sockets and chips pins.

Poly mode works except two dead’s keys in poly mode but not osc synth mode. Flipped up keyboard and cleaned those socketed chips. No luck still 2 dead keys in polymode only. One’s the low G the other the highest A.

Any ideas throw em out there

Thx

[guest]

for the dead keys, id look at the contact busbar in the keybed. usually its a broken or dirty contactor. as for the VCO, see if the CV is getting to it. there should be a a change of 18mV/oct on the base of the expo pair.

[guest]

just noticed its a DCO, so no expo pair. those schematics are pretty hard to read, and im still trying to figure out how it works.

[Fetaldreamcore]

Yes! Horrible schematics. And missing boards too I think. I was chasing continuity before I called it a day. Correction - It’s the low G and upper B key. I have “keybus” contact for those two dead keys which is the spring style against a rail but I’ll scrub it really well tmrw again. I Traced both dead keys to the multi molex and pinged it a couple places on both male and female molex portions. I’ll look further tmrw but also suspect just basic open contact somewhere for those.

The OSC issues are deeper and I’m trying to think where they might be. Osc 1 experienced a volume loss which I couldn’t recover. For a brief moment it was deep and full volume at the same level as the poly mode and the noise circuit. Then it lost more than half volume. It’s tracking pitch up the keyboard again for osc 1 and poly mode is huge sounding. Osc 2 just nothing.

[guest]

i found some pictures of the internals, and that helped me a bit. you can probe the 74ls221 ICs directly to see if they are producing square waves. the issue might be down the line from the oscillators.

[Troubleshooter]

Hi,

I have been trough 2 DS-2's they are not too hard to service but aren't easy either. Documentation isn't very good, that's the main reason.
Remember that a new lorlin switch has to be set with a notchy spacer for the amount of positions.

https://www.musikding.de/Rotary-switch-2P6T-sealed.