Dead Power Meter in SAE Mark 24

Glen B · 8th July 2006, 06:47 PM

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.

anatech · 8th July 2006, 06:53 PM

Hi Glen,
Test the diodes then. You have a meter?

-Chris

Glen B · 9th July 2006, 08:24 AM

Yes I have a meter. I just wanted to be sure I was on the right track. Thanks.

anatech · 9th July 2006, 12:22 PM

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

jackinnj · 9th July 2006, 05:45 PM

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.

Glen B · 9th July 2006, 09:35 PM

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

anatech · 9th July 2006, 09:57 PM

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

Glen B · 9th July 2006, 10:18 PM

I will take a look at those.

Glen B · 21st July 2006, 05:53 PM

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.

anatech · 21st July 2006, 06:03 PM

Hi Glenn,
Good going! I like people who recycle.

-Chris

8th July 2006, 06:47 PM	#1
Glen B diyAudio Member Join Date: Feb 2005 Location: New York	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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8th July 2006, 06:53 PM	#2
anatech diyAudio Moderator Join Date: Jun 2004 Location: Georgetown, On	Hi Glen, Test the diodes then. You have a meter? -Chris

9th July 2006, 08:24 AM	#3
Glen B diyAudio Member Join Date: Feb 2005 Location: New York	Yes I have a meter. I just wanted to be sure I was on the right track. Thanks.

9th July 2006, 12:22 PM	#4
anatech diyAudio Moderator Join Date: Jun 2004 Location: Georgetown, On	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

9th July 2006, 09:35 PM	#6
Glen B diyAudio Member Join Date: Feb 2005 Location: New York	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

9th July 2006, 09:57 PM	#7
anatech diyAudio Moderator Join Date: Jun 2004 Location: Georgetown, On	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

9th July 2006, 10:18 PM	#8
Glen B diyAudio Member Join Date: Feb 2005 Location: New York	I will take a look at those.

21st July 2006, 05:53 PM	#9
Glen B diyAudio Member Join Date: Feb 2005 Location: New York	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.

21st July 2006, 06:03 PM	#10
anatech diyAudio Moderator Join Date: Jun 2004 Location: Georgetown, On	Hi Glenn, Good going! I like people who recycle. -Chris

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