• The move to the new server is done. There are some software and database maintenance updates in process. This has us passing the hat around to help out. We appreciate any donations. Seriously, even a dollar helps. The payment page may be found here - https://www.audiokarma.org/support.html

How to measure continuity for correct ground on MC50?

T

telecowboy

New Member
I'm trying to measure the continuity across my MC50 with a DMM and I'm having issues. I have the amp unplugged from power and disconnected from any inputs and interconnects. With my DMM in continuity mode, I'm touching the black probe to the chassis and the red probe to both prongs on the power cable and there is no reading.

DMM is working when I touch probes together. Am I measuring this incorrectly? I just want to make sure the amp is grounded properly. Thank you!
 
Register to hide this ad
telecowboy said:
I'm trying to measure the continuity across my MC50 with a DMM and I'm having issues. I have the amp unplugged from power and disconnected from any inputs and interconnects. With my DMM in continuity mode, I'm touching the black probe to the chassis and the red probe to both prongs on the power cable and there is no reading.

DMM is working when I touch probes together. Am I measuring this incorrectly? I just want to make sure the amp is grounded properly. Thank you!
Click to expand...
Those are correct readings, there should be no measurable continuity or resistance measurement from either power plug prong to chassis.
 
Last edited:
Pio1980 said:
That is correct readings, there should be no measurable continuity or resistance measurement from either power plug prong to chassis.
Click to expand...
Thank you! Besides determining the correct polarity of the ac power cable, are there any other measurements I should take with my DMM for safety or performance?
 
telecowboy said:
Thank you! Besides determining the correct polarity of the ac power cable, are there any other measurements I should take with my DMM for safety or performance?
Click to expand...
On the older units without polarized power plugs, power plug orientation is random. Sometimes, reversing the plug(s) may help reduce background hum if it occurs.
 
The original cord should have a smooth and ribbed side, which will help. I don’t know if there is/was a standard but I always used the ribbed side for hot and the smooth for neutral. You can pull the bottom panel and see which one is connected to the fuse, that is the one I prefer to use for the hot leg which later became the (safety) standard in polarized plugs (the large blade is neutral and small blade is hot in the US). If this causes hum, rotate the plug and try again.
 
Pio1980 said:
On the older units without polarized power plugs, power plug orientation is random. Sometimes, reversing the plug(s) may help reduce background hum if it occurs.
Click to expand...
Are you saying it can change day to day? Yes I'm struggling with 60Hz hum but flipping it doesn't usually make a difference.
 
SaturationPt said:
The original cord should have a smooth and ribbed side, which will help. I don’t know if there is/was a standard but I always used the ribbed side for hot and the smooth for neutral. You can pull the bottom panel and see which one is connected to the fuse, that is the one I prefer to use for the hot leg which later became the (safety) standard in polarized plugs (the large blade is neutral and small blade is hot in the US). If this causes hum, rotate the plug and try again.
Click to expand...
Is the rib one tiny line on one side? I've looked before and never noticed it but now I do. I will try and see if I can tell a difference this time. Thanks!
 
Pio1980 said:
It shouldn't change randomly, it's the plug-in reversability that's random.
If changing plug orientation doesn't help, the problem is something else.
Click to expand...
Both seem to be the same amount of noise but I would feel a bit more charge on the chassis one way vs. the other in prior testing.
 
You must log in or register to reply here.
Back
Top Bottom