jaytee

One MB-6582, One Power Supply: a Tutorial

71 posts in this topic

i've done it both ways and I dont see any difference one way or another.  If I had to do it again, I'd use the 7809, cheaper and smaller.

One thing I'd recommend (unrelated to this question):  DONT use the E series recoms, they are super cheap for a reason and not well suited for audio applications,  Output noise is unacceptably high 

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I have noticed a few recent questions about how to power the MB-6582, so I figured I'd give this thread a little bump to make it easier to find.

Additionally, I went ahead and added this tutorial to the wiki like I promised I would over a year ago. It's live now, and I went ahead and edited the main page to add "PSU Option E" to the list of power options. Hopefully this makes things easier on novice builders.

Incidentally, I also cleaned the main MB-6582 wiki page up a little, removing some severely outdated links and adding links to the Modular Addict MIDIbox store. No more link to Wilba's 6582 megasale that hasn't been happening for over 10 years!

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Posted (edited)

Slightly odd issue: I have a working mb6582 with this power supply set up. However if any of the separate stereo outs are plugged this disables the power switch so that whenever the 7pin DIN is plugged the synth is powered on. 

I assume they are somehow providing ground when plugged. If they are plugged via a ground loop destroyer then the issue is removed. Currently I just have the mb6582 plugged via a surge protected plug. I don't think this is really a very serious issue, but just thought I'd mention it in case anyone can immediately tell what I've done! It is a bit odd/annoying so eventually I will investigate properly I guess. 

 

Edited by the_duckchild

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That’s...weird. I’ll have to check my own MB-6582 to see if I get the same behavior. I only ever use the mix out jack so I’m not sure I would have ever run into this.

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I noticed the same thing: the switch action removed the 0V rather than +V. It can be confusing when the MB-6582 "receives" 0V from somewhere else.

From memory, it would not be so significant if the bridge rectifier was still there. 

 

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ah, thanks -  well that's useful to know that it is possibly just a consequence of this set up rather than something I connected I shouldn't have. When I get the chance will try and trace why it happens, but it at least seems to be a reasonably trivial issue so far.

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Seems to me the bridge rectifier could be added back in without any issue, if that’s what causes the problem?

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good place to start thinking anyway. I think I need a good look at the schematic to understand why that would help.....

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Thanks for this tutorial. I followed and had a working power supply on my unit. I have just been doing some final troubleshooting of the switches on the control surface and the power supply has failed. I've still got 9v on the 9v rail, but only 1v on the 5v rail and the switching regulator is getting really hot. I hadn't been changing anything in the power supply area, just messing with the control surface. I did plug a stereo jack into the core 1 socket right before this happened.

My thinking is I need to replace that switching regulator for 5v, but I'm cautious to understand what caused this. It does appear to be still doing something, just outputting well below the voltage it should. 

Any thoughts?

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argh, I feel your pain when you're so close to finished!

Maybe recheck any new soldering you did do with a magnifying glass? - the 5v rail runs a LOT of places, so any changes you've made it's not impossible they're shorting something somewhere that's causing it. I definitely did this once or twice in what seemed like innocuous places. It's really easy to accidentally ground the ribbon cables for example.


 

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@the_duckchild agreed on a potential unwanted short, it can happen quickly - @oliq could you measure resistance between 5V and GND with a multimeter?

What happens if you run the PSU unloaded? Does it still hover at 1V and the switcher gets hot? If that happens, you've killed the switching regulator, but i'd think this probably would not happen often, i'd rather expect a problem on the board. If you can separate control surface from baseboard, recommend to do that, to find the short :).

Many greets and good luck!
Peter

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Thank you both, really appreciate your ideas.

I'll have a look at implementing them tonight. Just wanted to ask what you mean Peter about running the PSU unloaded, how would I do that? Sorry for my ignorance! I've removed the ICs for now to avoid damage.

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@oliq sorry if it was unclear, if you have not done it before, the idea was just disconnect the PSU from your MB6582 and measure the voltages the PSU provides "unloaded", without being attached to any device.

I'd half expect that you don't have a problem with the switching voltage regulator itself, as these are often normally protected against a lot of things like shorting, overcurrent, overtemperature...

That way you can find out, if the PSU really has a problem or (and that in conjunction with measuring resistance between 5V and GND rails) if one of the boards (baseboard or CS) has a problem. In the best case, you would just remove the short (when you find it) and the PSU should continue to work, no replacement of the voltage regulator necessary.

Many greets and good luck!
Peter

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PS: if you are not using an external switching voltage regulator, please forget my recommendation to test it "unloaded", as that is impossible, sorry for the confusion, hehe! :)

Next up then would be to measure between 5V and GND and separate the boards to find on which board the problem is.

Many greets!
Peter

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@HawkeyeThanks! Ah yes I did that, thanks for clarifying the terminology. My external PSU is still delivering 12v without being connected, and also 12v coming into the power in jack on the PCB when it is connected. I'll check for shorts where I was working when I get home later. I suspect it is the base board as I was trying to track down another problem and resoldering some joints just before it happened.

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Only had time for a quick test this evening, but yes, there's some continuity between 5v and ground. Now to hunt down the short...

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Ah, sorry, replied on your other thread, didn’t see that you had posted here and already gotten the same advice. :decayed:

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My first test showed constant continuity between the ground and 5v. Some checking and fixing a couple of suspect looking joints and it's now just showing continuity briefly when I first connect the probe.

I've disconnected the control surface and that's fine, the short is on the main board.

Also took of the DC convertor and that's working fine on it's own directly connected to the PSU I'm using.

I guess it's just a case of continuing to hunt for a short on the main board. Visually I've inspected the whole thing and it's not obvious to me yet...

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If you’re only briefly showing continuity when you first connect your probe (ie you get a short beep but then everything seems good) then it’s probably fine. That will often happen because your meter is charging a capacitor, allowing current to flow, which very briefly looks like continuity to the meter.

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@jayteeIt was still dropping the 5v to 1v, but eventually I fixed the problem. I am not entirely sure where it was as I went through a very long process of checking for shorts and reseating ICs. Anyway, it's working now, I have sound from my two SIDs, information on my screen and lights on my control surface. Now to sort out the buttons that still aren't working, so will return to my CS troubleshooting on the other thread. 

Thanks @jayteeand @Hawkeyefor you help with this one. It was a total pain but I have come out the other side with a better understanding of how this machine works thanks to your advice.

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