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Old 3rd January 2003, 06:42 PM   #1
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Unhappy HELP! i swapped plus and minus!

Hey
after my aleph3 had worked very well, i decided to install new rectifiers. But i swapped the Plus and Minus wire! The transformer was humming and the 0.47 Ohm resistance at the MosFets (located at the bottom of the schematic) got very hot. After turning off and recognizing my failure, i measured the capcacitors resistance (they didnt explode). It was at 0 Ohm! I think they are broken now, what else may be broken? The MosFETs? I dont want to turn it on again after everythings allright..
Pleas help me, i need only some inormation, what values i can measure when the amp is turned off...
I have a 500VA 2x18V transformer.
Regards,
Smithers
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Old 3rd January 2003, 06:52 PM   #2
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Because the output Mosfets have a reverse diode built in,
there is a good chance that nothing is broken. You will
want to check the supply caps for leakage with a positive
voltage across them. If I were you, I would correct the
polarity and fire the amp up with a Variac, watching the
current and voltages as I did so.
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Old 3rd January 2003, 06:53 PM   #3
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I would suggest that you start by disconnecting parts one at a time and testing each part. I wouild guess that all or most of the solid state parts are damaged or stressed. Reverse bias on transistors and FETs is very bad. Any resistors that got hot should be replaced also. The electrolitic caps may be OK yet depending on how long the reverse voltage was applied.

Good luck (you'll need it)

Later
Bruce

PS By all means follow Nelson's advice. Just be ready to change some parts.
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Old 3rd January 2003, 08:40 PM   #4
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Quote:
Originally posted by Nelson Pass
Because the output Mosfets have a reverse diode built in,
there is a good chance that nothing is broken. You will
want to check the supply caps for leakage with a positive
voltage across them. If I were you, I would correct the
polarity and fire the amp up with a Variac, watching the
current and voltages as I did so.
Wow, i cant believe, the master himself is helping me!
My supply caps are working, and i did as you told me, nothing broke, everything is ok! Wonderful, i am so happy!! I think the 6 caps took most of the current and there wasnt much left for the solid state parts, am i right?
I guess it wouldnt be possible to do that with another amp.
Thank you!

Regards smithers
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Old 4th January 2003, 12:45 AM   #5
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Actually I did this same thing on my first Aleph 2. It did take out one MOSFET, and blew R-15 to a sudden heat death quickly. And this was running it up on a variac....got to about 60 volts before I realized I had made a mistake......I was in a rush to see the blue LED light up .

I took the output stages back off the amp and checked them to find only a single blown MOSFET on the current source side, and all on the driver board was ok except for R-15. I would check everything carefully before you fire it up again. After I replaced the resistor, MOSFET and corrected the wiring mistake, it worked perfectly, and still is. The 2nd Aleph 2 worked perfectly at run up.

Reading 0 ohms on a capacitor does not necessairly mean its bad. Some meters take quite a while to "charge up" the capacitor....especially for very hi value capacitors. I suggest disconnecting the amplifiers from the power supply completely, re-wiring the bridge and then running the supply up by itself on a variac......bet its all ok. The rest of the amp you will have to check out part by part.
Mark
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Old 4th January 2003, 06:29 AM   #6
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Location: California
Default Re: HELP! i swapped plus and minus!

Quote:
Originally posted by Smithers
Hey
after my aleph3 had worked very well, i decided to install new rectifiers. But i swapped the Plus and Minus wire! The transformer was humming and the 0.47 Ohm resistance at the MosFets (located at the bottom of the schematic) got very hot. After turning off and recognizing my failure, i measured the capcacitors resistance (they didnt explode). It was at 0 Ohm! I think they are broken now, what else may be broken? The MosFETs? I dont want to turn it on again after everythings allright..
Pleas help me, i need only some inormation, what values i can measure when the amp is turned off...
I have a 500VA 2x18V transformer.
If you put two diodes (eg 1N5060) between the rails, eg:

Pos Rail --|<|-- --|<|-- Neg Rail w

and rail fuses on each rail, it'll steer the rails if you reverse them again and hopefully reduce or prevent damage to anything else on the rails.
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Old 4th January 2003, 06:52 AM   #7
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Unhappy Re: Re: HELP! i swapped plus and minus!

Quote:
Originally posted by schmad


If you put two diodes (eg 1N5060) between the rails, eg:

Pos Rail --|<|-- --|<|-- Neg Rail w

and rail fuses on each rail, it'll steer the rails if you reverse them again and hopefully reduce or prevent damage to anything else on the rails.
Hello,
ok i now but i havent ever swapped plus and minus in my whole life as an electronicamateur. and now everything is connected in the right way.
But, however, everything doesnt work well, one channel is ok, the other not. Dc offset at the outputs is ok, but theres no sound. i measuerd the voltage drops across the transistors and the resistors and everything is allright, the heatsinks of the left and the right channel get the same temperature. i think one of the irf9610 may be damaged, does anybody know what else i can do to getting to know whats the failure?
Thanks in advance,
regards smithers
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Old 4th January 2003, 07:45 AM   #8
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Hi,

now i am listening to music again, there was a badly soldered pin on the mainboard!
Thank you all,
regards,
smithers
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Old 4th January 2003, 02:37 PM   #9
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Smithers...I believe Phase Linear did that diode trick in their amplifiers of long ago......
Mark
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Old 4th January 2003, 09:46 PM   #10
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The power Mosfets include that diode, and they took most
of the current when the polarities were reversed.

In the case of the Phase Linear, the diodes are there to
prevent flyback from an inductive load destroying the outputs
when the current limiting kicks in.
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