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January 16, 2022, 05:15:51 AM

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Author Topic: SWR Workingman's 12 combo- Hummmmmm  (Read 368 times)

mikebarg

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SWR Workingman's 12 combo- Hummmmmm
« on: January 05, 2022, 05:04:32 PM »
Well this has been sitting on the bench waiting for me to get to it. It has a moderately loud hum. I have recorded it. I thought 60hz hum but, i checked the full wave bridge and the 2 main power capacitors. They all checked good. Any ideas where to go from here. See the video here https://youtu.be/mNbTI2KNZyI

Enzo

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Re: SWR Workingman's 12 combo- Hummmmmm
« Reply #1 on: January 05, 2022, 07:40:52 PM »
How did you check the caps?  Just because the value is close doesn't mean it i well connected.  Sounds like DC on the speaker to me.  If so TURN IT OFF or the speaker will be destroyed.

Does the speaker cone move one direction and stay when you power up?  Take the wires off the speaker and measure for DC voltage between them.

Otherwise check the solder on the main filter caps.  Check the main power rails for ripple.

mikebarg

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Re: SWR Workingman's 12 combo- Hummmmmm
« Reply #2 on: January 05, 2022, 09:31:30 PM »
I pulled the caps and tested them. The value and ESR both looked good. I re-installed them on the board. I also removed the full wave bridge and checked it out of circuit. It's good too.

mikebarg

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Re: SWR Workingman's 12 combo- Hummmmmm
« Reply #3 on: January 05, 2022, 11:21:28 PM »
I don't see any DC on the speaker output.

Enzo

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Re: SWR Workingman's 12 combo- Hummmmmm
« Reply #4 on: January 06, 2022, 12:31:37 AM »
OK, then the ripple?  You have a positive and a negative supply in there.  Are both up to about the same voltage and free of ripple?

mikebarg

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Re: SWR Workingman's 12 combo- Hummmmmm
« Reply #5 on: January 07, 2022, 09:39:52 AM »
Ok. one of the caps has no measurable ripple, but the other has .45 vAC.

mandu

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Re: SWR Workingman's 12 combo- Hummmmmm
« Reply #6 on: January 07, 2022, 07:25:07 PM »
Can you check if C7 (2.2 mF) in poweramp is OK?