[volt-nuts] Fluke 5205a Repair

Charles Steinmetz csteinmetz at yandex.com
Mon Sep 28 18:17:59 EDT 2015

David wrote:

>I am not certain I want to disable the OVERLOAD circuit to make this 
>adjustment without knowing what may be wrong for fear of doing more 
>harm than good.  But on the other hand, this may very well be 
>exactly what is causing the tripping in the first place.

What you need to do is determine whether there really is excessive 
current trying to flow from the generator, or whether the fault 
monitor is broken or out of adjustment.  So, I recommend focusing 
narrowly on whether the generator is or is not supplying current and, 
if it is, where that current is flowing.  This can usually be done by 
measuring voltages in situ and calculating currents through existing 
circuit resistances (sometimes you only get a fraction of a second 
after power-on if the protection circuit shuts the generator down 
rather than just limiting the current).  A clamp-on DC current probe 
can be handy, but is often not necessary.

As a side note, this technique (finding out where DC current is 
flowing, and how much of it) is a very powerful diagnostic 
tool.  Focusing on it can save untold hours of aimless poking around 
hoping to stumble on a clue.  "Hmmmm -- I know DC current is flowing 
into this node, where could it go?  The only possible paths to a more 
negative potential are through R115 or C13.  Measuring the voltage on 
both sides of R115, and confirming its resistance, I know that the 
current flowing through it is nowhere near the current flowing into 
the node.  Therefore, ...."

Best regards,


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