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AC adapter connection not idiot-proof!

chi1

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AC adapter connection not idiot-proof!

Postby Blindekinder » February 1st, 2016, 4:55 am

Hi,
some days ago, my great mini3+X1 worked the whole day for a synthesizer presentation, and made the job well, until it fell asleep, exhausted. So today I plugged it for charge, but I didn't remember the polarity of the plug. I tried both, didn't see the led lighting, so I tried both again, switched the device on to try, and experienced a great special effect for such a small thing, with a nice dense smoke coming out of the enclosure... U1 MCP73864-I/SL had burned!

I thing I'll have to buy a new board, since the ic was already changed after another accident. Unsolder it again seems quite impossible...
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Re: AC adapter connection not idiot-proof!

Postby amb » February 1st, 2016, 11:17 am

You must use a "center positive" adapter, and it must be regulated 9V DC. This is specified at the χ1 website.

You don't have to build a whole new board. See the χ1 website, on the "Initial check" page, under the "Notes" heading about how to remove the chip.

http://www.amb.org/audio/chi1/
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Re: AC adapter connection not idiot-proof!

Postby hagak » February 1st, 2016, 11:22 am

I suspect Blindekinder is using a universal AC adapter that allows you to switch the polarity. I strongly recommend not using these, I personally have fumble fingered them and damage a device myself. The concept of the universal AC adapter is great, but in practice it is less than stellar.
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Re: AC adapter connection not idiot-proof!

Postby Blindekinder » February 1st, 2016, 2:34 pm

don't worry, that was not a complaint, just a simple report...
I'm sometimes brutal and lazy with that, instead of taking a manual to verify and use a voltmeter to check polarity, I just try with the switch of my universal AC adapter, and normally it works, since many devices are protected.
Is the X1 normally protected against that or was it another issue?

remove the chip.

I already removed the chip once, and I remember the track was in a bad state then... I don't think it will support one more change.
But this is interesting to mention:
a track and both IC's burned because I didn't cut the legs short enough, so when I inserted board into enclosure, it made a shortcut. I was taught to let a mm or two after solder. In this case you have to cut them really tight!
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Re: AC adapter connection not idiot-proof!

Postby amb » February 2nd, 2016, 2:56 am

The χ1 circuit is not protected against reverse DC polarity or over-voltage, beyond what is tolerated by the ICs themselves. Polarity reversal protection typically use diodes that cause voltage drops. In order to maximize the Mini³'s output voltage swing, we want to avoid such diodes as much as possible (and there are already two of them at the χ1's output section by necessity).
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Re: AC adapter connection not idiot-proof!

Postby LV26 » February 5th, 2016, 11:31 am

amb wrote:The χ1 circuit is not protected against reverse DC polarity or over-voltage, beyond what is tolerated by the ICs themselves. Polarity reversal protection typically use diodes that cause voltage drops. In order to maximize the Mini³'s output voltage swing, we want to avoid such diodes as much as possible (and there are already two of them at the χ1's output section by necessity).

MOSFET as Diode (AKA Ideal-Diode) with very small voltage drop can replace ordinary diodes.
Everything should be made as simple as possible, but not simpler. // Albert Einstein
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