Reply 40 of 44, by Spikey

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InTheStudy wrote on 2024-03-23, 11:06:
That's really, really sweet of you - but I wouldn't be able to accept a $300AU gift from someone even IF I thought it was fair f […]
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Spikey wrote on 2024-03-23, 10:41:

Good luck for sure on all counts. I do have a SC-D70 that I'm unlikely to use again, one of the switching ones, and I can send it to you, if yours is dead.

That's really, really sweet of you - but I wouldn't be able to accept a $300AU gift from someone even IF I thought it was fair for you to "make good", which I don't. We're cool as a Cactuar, Spikey. 😀

I'm optimistic, so let's just see how it goes with the tech next week. In the meantime, I'm gonna take a look at printing a couple of half-rack cases, for the MT-D47 and the World's Worst Recording Studio. 😀


Optimism, Captain!

Study, are you in AU?

Reply 43 of 44, by momaka

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Just some info to pass down to your tech friend: if the fuse is blown and this is a SMPS (switch mode power supply), chances are the MOSFET and its source resistor are dead too. PWM controller also gets damaged sometimes... if there is one in this SMPS (some designs use oldschool 2-transistor self-oscillating circuit.) That being said, if the SMPS has a "standard" voltage output (i.e. 3.3V, 5V, 12V, 24V, etc.), it might be just cheaper to replace the SMPS module with another one that outputs the same voltage and call it a day. Also, in the case of SMPSes, a blowout on the primary rarely causes damage to the secondary, so the rest of the unit should be fine... though I certainly hope I'm not jinxing it by saying this. 🙁

What's indeed puzzling is why the PSU blew after 2 minutes and not instantly. If the SMPS has a 400V (DC) input cap, then it really should be a "full range" 100-240V AC input -capable. Stuff that's built strictly for 110/120V AC for the USA (and Japan) typically carry 200V (DC) -rated input caps only, as they are much smaller and cheaper, and it makes a lot of sense from a manufacturing standpoint to save on costs with a simple part swap right there. So it looks as if it was built as a universal / full-range SMPS, but then wasn't? Again, really puzzling why the PSU manufacturer would do this.

Relating to this... I recently moved from the USA to Europe and brought a few electronics with me. One of them was a surround sound system rated for 120V AC input only and accordingly has only a 200V DC -rated input cap. Being an SMPS, I swapped it with a 400V cap as a cheap attempt at converting it to European voltage system. However, through careful testing, I have found that this is a no-go in the long term, since the US version of the SMPS also lacks some other components in the snubber circuit, making the main switching MOSFET dissipate 2x more power (i.e. 2x more heat). If left this way, it seems like it could certainly overheat and blow. Mine can run for 5-10 minutes, but gets very hot afterwards, so certainly I have to do a bit more work to make it a proper 230/240V AC conversion. But at least I could observe the PSU was built for 120V AC only. In the case of the Rolland SMPS, we still can't get a clear picture if that was the case or not. Thus I also think the possibility of the PSU blowing due to something else is not out of the question quite yet.

Anyways, hopefully we get an answer to this and hopefully your unit will work again with an inexpensive repair.

Reply 44 of 44, by InTheStudy

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Thanks Momaka, I self-evidently have no idea what I'm doing - but my technician does so I'm trying not to get TOO preachy at him.

The latest news is predictably double plus unpositive, once the fuse was replaced; Popcorn was connected to the mains through the step-down transformer and apparently, the line filter coil immediately started smoking. So, investigations continue and your suggestion may very well be on the money. I did find reference to the pinout of a SMPS module used in other synths like the SD-80 which is *apparently* very similar. If that's the case, then (again, assuming no bad voltages made it to the analog or digital boards, in which case I'm just screwed) it should be possible to build a complete replacement - possibly even moving the mains stage out of the unit entirely, which would be nice. But for now; in the words of a great Scottish poet - we wait, with baited breath.

As for Mew, tech doesn't have a 2032 coin cell holder that will fit; so he's going completely overkill and ordering a 2477 holder - which should keep the thing powered till the heat death of the universe.