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Old 8th July 2006, 06:47 PM   #1
Glen B is offline Glen B  United States
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Default Dead Power Meter in SAE Mark 24

Any SAE experts here ? Your help would be appreciated. I just acquired a mint condition SAE Mark 24 amp. Both channels are playing fine but one of the power meters is not functioning. I disconnected the meter from its drive board and applied a small voltage to it. The needle deflected full scale, leading me to believe the problem is elsewhere, likely with one or more of the diodes on the drive board.
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Old 8th July 2006, 06:53 PM   #2
anatech is offline anatech  Canada
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Hi Glen,
Test the diodes then. You have a meter?

-Chris
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Old 9th July 2006, 08:24 AM   #3
Glen B is offline Glen B  United States
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Yes I have a meter. I just wanted to be sure I was on the right track. Thanks.
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Old 9th July 2006, 12:22 PM   #4
anatech is offline anatech  Canada
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Hi Glen,
You are on the right track. Those meter movements are 1 mA for full scale deflection at the most. 100 uA is common as well. An ohm meter in a DVM locked a few scales up from the bottom would be safe to test the meter with.

You may want to consider replaced the electrolytic capacitors with new ones on an amp that age. Nice acquisition BTW.

-Chris
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Old 9th July 2006, 05:45 PM   #5
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Default Re: Dead Power Meter in SAE Mark 24

Quote:
Originally posted by Glen B
Any SAE experts here ? Your help would be appreciated. I just acquired a mint condition SAE Mark 24 amp. Both channels are playing fine but one of the power meters is not functioning. I disconnected the meter from its drive board and applied a small voltage to it. The needle deflected full scale, leading me to believe the problem is elsewhere, likely with one or more of the diodes on the drive board.
fwiw, never test a meter without current limiting device of some sort -- even a "small" voltage can destroy the meter coil.
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Old 9th July 2006, 09:35 PM   #6
Glen B is offline Glen B  United States
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Chris, Jack,
Thanks for the advice. The main power supply caps look new like they are replacements. They appear identical to current stock at Allied Electronics of the same brand, value, voltage and temp rating.

Glen
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Old 9th July 2006, 09:57 PM   #7
anatech is offline anatech  Canada
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Hi Glen,
If the main filters are new, that's great! I am also concerned with all the coupling and bypass caps in the circuits.

-Chris
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Old 9th July 2006, 10:18 PM   #8
Glen B is offline Glen B  United States
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I will take a look at those.
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Old 21st July 2006, 05:53 PM   #9
Glen B is offline Glen B  United States
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I just wanted to follow up on this problem. The diodes tested fine. A pin on the meter circuit board to which the output is connected apparently had a fracture (don't know how that happened) and snapped off very easily while I was checking out the board. I removed the stub from the meter board, installed a new pin and the meter is now working fine. I also recapped all of the boards in the amp and it is now singing beautifully.
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Old 21st July 2006, 06:03 PM   #10
anatech is offline anatech  Canada
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Hi Glenn,
Good going! I like people who recycle.

-Chris
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