Nuub A30 16V offset H-E-L-P!

chipco3434 · 30th January 2006, 12:20 AM

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...

MikeW · 30th January 2006, 12:56 AM

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.

chipco3434 · 30th January 2006, 01:21 AM

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?

mpmarino · 30th January 2006, 04:15 PM

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

chipco3434 · 5th February 2006, 09:41 PM

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!

MikeW · 6th February 2006, 06:02 PM

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.

chipco3434 · 6th February 2006, 06:28 PM

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!

mpmarino · 6th February 2006, 07:31 PM

Quote:

I did NOT know they had to be grounded to work?????

you have the output fets grounded?

chipco3434 · 6th February 2006, 07:38 PM

No, the amp board.

mpmarino · 7th February 2006, 02:56 AM

Quote:

No, the amp board.

you have the amp board grounded?

30th January 2006, 12:20 AM	#1
chipco3434 diyAudio Member Join Date: Feb 2004 Location: Racine, Wisconsin	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...

30th January 2006, 04:15 PM	#4
mpmarino diyAudio Member Join Date: Jun 2004 Location: Crunchville, where I don't fit in.	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 __________________ Crazy Yankee.

6th February 2006, 06:02 PM	#6
MikeW diyAudio Member Join Date: Sep 2002 Location: North of Boston	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. __________________ MikeW

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30th January 2006, 12:56 AM	#2
MikeW diyAudio Member Join Date: Sep 2002 Location: North of Boston	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. __________________ MikeW

5th February 2006, 09:41 PM	#5
chipco3434 diyAudio Member Join Date: Feb 2004 Location: Racine, Wisconsin	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!

6th February 2006, 06:28 PM	#7
chipco3434 diyAudio Member Join Date: Feb 2004 Location: Racine, Wisconsin	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!

6th February 2006, 07:38 PM	#9
chipco3434 diyAudio Member Join Date: Feb 2004 Location: Racine, Wisconsin	No, the amp board.

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