[Boatanchors] 5+ megohms primary?

[Troglodite at aol.com]

In a message dated 11/11/04 10:23:18 AM Central Standard Time,  
StephenTetorka at cs.com writes:

With no  power supplied, when using a VTVM from either primary lead to ground 
of the  main power transformer, I get a reading of 15 megohms with the SPST 
in the  primary in the OFF position.
I get 5 meghoms in the ON position - which  completes one primary leg circuit 
allowing the 115 VAC to  primary.



Steve,
 
Firstly, 15megohms leakage isn't all that bad. If it is all in the  
transformer it will get better as the transformer is run, warms up, and drives  out 
residual moisture. The chassis of the power supply should be connected to an  
earth ground anyway, either via a 3-wire cord or a separate, secure  connection.
 
What worries me is that you see a difference depending on the state of the  
on off switch. I assume nothing else is connected? Look carefully for any line  
bypass capacitors that might be present from one or both sides of the line to 
 the chassis. If you find line bypass capacitors, these should be replaced.  
If there are none, then you have some additional leakage somewhere, which is  
showing up when the switch is in the ON position. It's still not that bad at 5 
 megs, but it's a bit of a puzzle. It could be from carbon paths inside the  
switch caused by arcing when the switch is operated. Unscrew the switch from 
the  chassis so the mounting boss is not grounded and see if that affects the  
reading. If it does, then replace the switch.
 
Doug Moore  KB9TMY