Nuub A30 16V offset H-E-L-P! - diyAudio
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Old 30th January 2006, 12:20 AM   #1
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Default Nuub A30 16V offset H-E-L-P!

Fired up my Mini/30 four channel... seperate power supplies for the Mini & the 30. Big problemo...

One of the A30 channels is 16 volts offset. I haven't cooked anything yet but I reckon this isn't good. All the other channels are ~0.025VDC.

Where do I start?

Thanks

EDIT: This is the BrianGT board...
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Old 30th January 2006, 12:56 AM   #2
MikeW is offline MikeW  United States
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1. Make sure there are no solder bridges.
2. Check the input MOSFETs. Most of the time one of them is blown up. They shouild have all the same voltage drops as the good channels.
3. Check the output mosfets for shorts. If you can disconnect them. Take them out.
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Old 30th January 2006, 01:21 AM   #3
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Quote:
2. Check the input MOSFETs. Most of the time one of them is blown up. They shouild have all the same voltage drops as the good channels.
Q1, Q2, Q3, correct?

I had to desolder these and most likely cooked them up pretty good. Chances are good that I pooched them, eh?
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Old 30th January 2006, 04:15 PM   #4
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I'd bet a dollar MikeW is right.(#2 his reply) One of your matched fets in the diff pair is probably toasted. Don't ask me how I know...about 5 times
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Old 5th February 2006, 09:41 PM   #5
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I replaced the input FETs with exactly the same results...

no evident solder bridges or cold joints

Should I disconnect everything connected to the output boards?

For testing, where do I put the probes and what voltage am I looking for, where?

Sorry to be so stupid, this stuff usually works!
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Old 6th February 2006, 06:02 PM   #6
MikeW is offline MikeW  United States
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3. Check the output mosfets for shorts. If you can disconnect them. Take them out.
The voltages are on the service manual schematic if you have a copy.
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Old 6th February 2006, 06:28 PM   #7
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I had enough output FET's to redo some boards and did some disassembly and reassembly etc. Got the new channel down to 4 mV so that's cool. It was a little wierd that I had this stuff all over the desk and I had no output to speak of and cold chips... I did NOT know they had to be grounded to work?????

Well anyway, other than putting humpty back to gether again, everything is VERY COOL... well actually pretty warm!
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Old 6th February 2006, 07:31 PM   #8
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I did NOT know they had to be grounded to work?????
you have the output fets grounded?
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Old 6th February 2006, 07:38 PM   #9
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No, the amp board.
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Old 7th February 2006, 02:56 AM   #10
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No, the amp board.
you have the amp board grounded?




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