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Author Topic: MFB 522 (Another one of those PSU F**K up threads)  (Read 503 times)

boneless

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MFB 522 (Another one of those PSU F**K up threads)
« on: April 27, 2018, 11:07:26 AM »

I needed a spare PSU for my lovely MFB 522. The bottom spec of the unit said 15v DV 300mA

So I bought this from Ebay, plugged it in, only to get a loud hum and smoke.

 :( 

 

Amazingly the voices of the unit still work with the original PSU but the ON push switch is permanently ON and it still stinks.

An email from Mr MFB himself he said if I send it back they can repair it.

He also said this PSU should work

https://www.conrad.de/de/steckernetzteil-einstellbar-mean-well-gs12e15 -p1i-15-vdc-800-ma-12-w-1294174.html

But it's in Germany.

Firstly I wondered if anyone can help me source a suitable UK alternative that isn't going to fry my machine?

Secondly I wondered if circuitbenders HQ think they can mend it thus saving sending to Europe and back.

And thirdly, does anyone know WTF went wrong?!

I checked polarity and V before I plugged it in. Polarity was right and volts was slightly high at about 19 I think.

Thanks all...
« Last Edit: April 27, 2018, 04:05:34 PM by boneless »
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Re: MFB 522 (Another one of those PSU F**K up threads)
« Reply #1 on: May 31, 2018, 12:51:08 AM »

Are you sure the polarity is right? I note it doesn't actually say the polarity on the PSU. The one on that link is centre positive by the look of it.
Having said that, you'd like to think that an MFB522 would have some kind of polarity protection.

What are the specs on the original power supply. A linear unregulated PSU like the one in the photo will always test with a slightly high voltage when its not under load. The voltage will drop when something is pulling current, so the 15v DC quoted is probably what it will supply when something is pulling near 300ma. On paper it should be fine.

Is the only issue that the power switch is permanently on? If so it can't be hard to just source a new one

The only thing i can think of that might have gone wrong is that power supply is actually outputting AC and not DC.

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boneless

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Re: MFB 522 (Another one of those PSU F**K up threads)
« Reply #2 on: June 03, 2018, 03:12:21 PM »

Thanks for the reply, very helpful....

Still not sure what happened, but the plug on the original PSU is very slightly differnet from the one that fried things inside. Same external diameter, but the original PSU has a yellow bit of plastic at the end.

https://upload.wikimedia.org/wikipedia/commons/thumb/e/e3/EIAJconnector2_edit.jpg/1280px-EIAJconnector2_edit.jpg

The one I used didn't, so I think it must have earthed the current to ground, possibly thorugh the power switch?

https://www.schneidersladen.de/media/catalog/product/cache/1/image/9df78eab33525d08d6e5fb8d27136e95/i/m/image_26537.jpg


The power switch is a push on/off so probably quite a cheap component, and I guess melted the mechanism?

This is me guessing with very patchy knowledge so no idea if it's plausible or not!!!! :o

Anyone have any idea if I could desolder the switch, and put another in? Having power on/off would be helpful as I have it wired into my home studio, so whenever I fire that up, it's on, whether I use it or not.

I have now started to pay much more attention nuances of the differnt plugs on PSU's!

Anyhow, have sourced a new PSU, with the same yellow plug, and slightly higher mA that works, but would still like to 'fix' it as it bugs me when stuff doesn't function as it should.

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