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How do you check for voltage on the chassis?


 
9/29/2005 9:22 AM
Ricky How do you check for voltage on the chassis?
I suspect that some voltage may be getting on the chassis somehow. How does one check for it?
 
9/29/2005 11:20 AM
Dai Hirokawa
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meter on AC, touch one probe to chassis, hold the other one. If there is a big AC voltage like 60 or 100VAC or whatever, and you are touching that chassis directly or via a gtr. cord, then you touch something else metal like a mic which is 0VAC or much lower you'll get shocked. Least that's how I understand it.
 
 
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9/29/2005 12:07 PM
Ricky Yikes, I have voltage...what now?
Ok, Checked it using the AC meter method. I have 15-25 volts there. This has got to be te source of noise.(hummmmm - midrangy)I assume it should be zero? I guess I should dissconnect legs of the star gounds one at a time to see what point is putting off the voltage?
 
9/29/2005 2:10 PM
loudthud
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Back to square one
What country are you in and how many wires in your line cord ?  
 
There will always be some voltage on the chassis if it is not connected to anything due to small leakage currents in the power transformer. This is what the death cap is supposed to eliminate in the US. When the death cap was connected to the hot side of the line, it put full line voltage there and you were supposed to reverse the (then 2 wire) line plug or switch the ground switch to the other position. The three wire line cord eliminates this by conducting those leakage currents to ground thus making the voltage zero volts or pretty close.
 
9/29/2005 4:01 PM
Ricky
US- 3 line power cord. My ground is not connected however(at the wall - old outlet)
 
9/29/2005 1:36 PM
Paul Drexhage Re: How do you check for voltage on the chassis?
I suppose you could lift the chassis from ground (if it is grounded via a three prong cord), and place an ammeter in series with the chassis and true earth ground. If you're drawing a significant amount of current, you probably have a problem somewhere. I believe this is the method used for UL certification.
 
9/29/2005 3:17 PM
Dai Hirokawa
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I'm not sure that a bit of AC volts necessarily spells trouble. What exactly are you trying to accomplish? Are you trying to chase noise down or?
 
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