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Help! I just fried a mini-Aleph (Polarity reversed)
Help! I just fried a mini-Aleph (Polarity reversed)
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Old 10th December 2006, 08:10 AM   #1
Russell Sit is offline Russell Sit
diyAudio Member
Join Date: Jul 2002
Location: Texas
Default Help! I just fried a mini-Aleph (Polarity reversed)


I have acquired a pair of stuffed mini-Aleph board from a friend on the internet. After soldering the RCA jacks and speaker connectors last night, I hooked one board to a laboratory power supply. I supposed there is a convention system on power supply polarity i.e. Left-positive, Right-negative. It turned out that I was xxxxxx wrong! It is just the reverse in my power supply.

Not realizing this, I thought I was pretty safe to start from 0v. After 2v at the true negative side, the voltage cannot be increased further, while the positive side could reached more than 10v. The next thing I noticed was smoke from the PCB. I immediately switched off the power supply. However, I could not identified where exactly was the smoke coming from.

Eventually I discovered the cause. The other board was singing beautifully with the right connection, 1 amp at +/-12V. There was quite high DC voltage (0.3v) at the output, though.

Then I decided to try my last hope and hooked up the smoked board again. (not sure if this is a recommended practice) There was a very small current (<50mA) through the negative supply, while the positive supply had about 700mA flowing in it. The voltage across the output is around 7v.

My very preliminary diagnosis is that the reverse in polarity has caused a marked increase in the current through the circuit supplied by the negative voltage. Therefore I could not increase the voltage further as the current drawn had already exceeded the rating of the supply. Then, the heat destroyed some components leading to an open circuit. So no current flows after the fry.

I am very very upset by my stupid mistake. I am not an EE, and I have no idea how to repair it. Could you please shed some light on this disturbed soul?

Thanks in advance for your kind help!

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