VOGONS


First post, by Galahad

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Please note: I originally posted this thread 2 days ago on the forum, but I think I may have accidentally posted it in the wrong sub-forum, and so I am just now reposting it here as I believe this sub-from may potentially be the most relevant to the topic at hand. Thanks!

Hello and greetings! I apologize in advance, since I know it has been quite a while since I lasted posted here on the forum. Question please: my CM-500 is currently behaving quite unusually in Mode B, and so I was just curious, can anyone kindly please help or advise if it is hopefully fixable or repairable?

The Mode B (also Mode A and D as well) technical issue being experienced: every time I turn on the CM-500 in Mode B, for the first few seconds, everything works fine, but then, suddenly, the volume level increases substantially, and the green light keeps flashing, continuously and indefinitely 🙁 When I load a classic PC game that uses Mode B, the issue appears to temporarily go away, but as soon as the game exits, it comes back full-force. Mode C appears to be blessedly unaffected. However, nothing I have tried to do to fix the Mode B has seemed to work out, including sysex reset, powering off and then powering back on the CM-500, manually loading a sysex reset in the Van Basco MIDI player or Windows Media Player, etc. The underlying PC system is a classic, ISA-bus PC that is connected to the CM-500 using an MPU-401/AT ISA card interface; i.e., a true MPU-401 interface, not running DOSBOX.

This CM-500 is really the crown jewel of my classic Roland synth collection since it is in excellent / mint / near-mint physical condition, so if it can hopefully be fixed in some way, I would much prefer to go that route if at all possible, if someone could please advise what might be the best course of action? I do have spare or extra/backup CM-500 devices that I could use in lieu of this unit in the event it is unable to be fixed, but since none of the other ones have the level of outstanding physical appearance of this device, again my most optimal preference would ideally be to get this unit back to full functionality if it can be done. Just for example, would an authorized or official Roland repair shop still be able to fix an older classic device like the CM-500? Or can it potentially be fixed in another way without having to go to a Roland repair shop, such as flashing or resetting the CM-500 BIOS, or something similar? Thanks!

Reply 1 of 8, by Galahad

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Bump please?

Reply 2 of 8, by Galahad

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Anyone? 🙁

Reply 3 of 8, by Deunan

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Your problem is very specific and the HW is also quite rare I think. I know next to nothing about CM-500 - I have CM-300 but I haven't been using it very much. Both my CM-300 and CM-64 take the input voltage and reduce it further to 5V via 7805 or something similar. These parts will become unstable if the nearby capacitors have too much ESR or too low capacitance. So in other words the first thing to rule out is unstable voltage regulation inside the unit. Then measure the ripple on the supply lines next to big ICs, if any cap is very marginal (or dead) you'll see excessive ripple. These are simple tests and worth doing before you start looking for repair shops.

Reply 4 of 8, by Galahad

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Deunan wrote on 2024-07-09, 18:09:

Your problem is very specific and the HW is also quite rare I think. I know next to nothing about CM-500 - I have CM-300 but I haven't been using it very much. Both my CM-300 and CM-64 take the input voltage and reduce it further to 5V via 7805 or something similar. These parts will become unstable if the nearby capacitors have too much ESR or too low capacitance. So in other words the first thing to rule out is unstable voltage regulation inside the unit. Then measure the ripple on the supply lines next to big ICs, if any cap is very marginal (or dead) you'll see excessive ripple. These are simple tests and worth doing before you start looking for repair shops.

Many thanks for your valuable input and feedback Deunan, I deeply appreciate it!

Thx again

Reply 6 of 8, by Galahad

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vetz wrote on 2024-07-09, 18:39:

I own a CM-500, but I've never experienced the same issues you are experiencing.

If you have a spare CM-500 that is in working order, could it be an idea to swap the cases to keep the pristine appearence?

Thank you for the helpful suggestion vetz!

Also just a quick follow-up question for you please: since I do not on my end currently have the technical expertise needed to arrange the case-swap as per your valuable input, could you please recommend a good or reputable place to take it to, to do this? Would I have to find an authorized Roland repair shop to do it, just for example, or would some place more generic like Best Buy or Micro Center, etc. be able to safely arrange it? Thx again

Reply 7 of 8, by Galahad

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Bump please? Thanks!

Reply 8 of 8, by vetz

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Galahad wrote on 2024-07-10, 16:08:

Also just a quick follow-up question for you please: since I do not on my end currently have the technical expertise needed to arrange the case-swap as per your valuable input, could you please recommend a good or reputable place to take it to, to do this? Would I have to find an authorized Roland repair shop to do it, just for example, or would some place more generic like Best Buy or Micro Center, etc. be able to safely arrange it? Thx again

It shouldn't be that difficult to do a case swap. Just a regular screwdriver is probably enough when it comes down to tools needed.

If you don't want to do it yourself, I'd check if there is any local retro computer groups on Facebook/Discord. Then ask there if anyone is interested for some beers/payment. I don't think any official Roland service point would do this kind of work. Maybe a mom-n-pop computer/phone repair shop could also take it on.

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