VOGONS


First post, by Masejoer

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I finally got around to setting up an older dos machine, with the necessary cable for MT-32 use. Both of my units don't appear to have working knobs? One started out having a master volume of 60, but after trying a reset to see if that'd help me change volume, it's now down to a volume of 2 (of 100). My second unit is already at a volume of 2. Music is of course extremely quiet on both now.

I press "Master Volume", and the knob does nothing. The knob actually does nothing on either unit, in any screen.

Did I somehow get two different units with failed potentiometers? Feels bad that I've been sitting on the machines for awhile, not knowing they don't appear to work on receipt?

Reply 1 of 6, by Masejoer

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Well, I opened one up. While the post and set nut are both fine and aligned, the rear of the potentiometer is damaged. Not sure how that would happen, nor how it would happen in transit - there isn't much weight hanging from the post. Either way, I'm guessing the second unit has a similar problem. Can't be a coincidence - perhaps an issue. Someone mentioned that theirs was covered in epoxy - perhaps Roland identified this issue and started gluing them for reinforcement?

The part number I found in a post here from 2015 doesn't seem to be available any longer. Plenty of 10k, but no 50k.

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Reply 2 of 6, by Jo22

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Masejoer wrote on 2022-06-27, 17:54:

The part number I found in a post here from 2015 doesn't seem to be available any longer. Plenty of 10k, but no 50k.

What about 47k? It's a standard value. 🙂

Edit: There are linear and logarithmic types, generally speaking.

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Reply 3 of 6, by Masejoer

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Jo22 wrote on 2022-06-27, 18:00:
Masejoer wrote on 2022-06-27, 17:54:

The part number I found in a post here from 2015 doesn't seem to be available any longer. Plenty of 10k, but no 50k.

What about 47k? It's a standard value. 🙂

Edit: There are linear and logarithmic types, generally speaking.

All I could find by searching octopart were 10k and 20k variants. Neither of which would be sufficient. I also tried using mouser's search to manually search by other specs/potentiometer type, but I ended up with only a single 10k range part.

I just opened my second unit, and it's the exact same thing. You'd think this photo was of the same unit.

The first one I opened was missing side screws (after seeing the second unit) - it's obvious someone had it open at one point, and didn't disclose that they knew there was a problem.

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Last edited by Masejoer on 2022-06-27, 18:41. Edited 1 time in total.

Reply 4 of 6, by pentiumspeed

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Pull knob and unscrew the pot, then pull through the front panel, keeping them together. Then examine the pot's body to see if you can put back together and re-crimp the metal hooks?

Cheers,

Great Northern aka Canada.

Reply 5 of 6, by snufkin

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Probably worth trying Pentiumspeed's suggestion of repairing the pot, I've had that work before. I had a quick look on Mouser and it looks like there are a few 50k pots:
https://www.mouser.co.uk/c/passive-components … ~Product%20Type

Finding one that fits could be tricky. Maybe the Bourns PTV09 series? https://www.mouser.co.uk/datasheet/2/54/ptv09-777818.pdf

Reply 6 of 6, by jesolo

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I had a similar issue with my MT-32 that I bought (but my problem wasn't as severe). I noticed that my volume control was also not functioning properly and I basically did what @pentiumspeed suggested and it worked fine afterwards.