Certainly glad to expand on the check of fuses or switches. It is a
continuity check. Your ohm meter instructions should cover that.
But, in general, you check on the lowest ohms range of a DVM, or DMM
properly, or VOM. All these meters typically have an ohms range and
better meters have several. You want the lowest range to force some
current through the fuses and see if the connections are near zero ohms.
Expect even shorted test leads to have some resistance say 0.9 ohm, is
typical. Some meters allow adjusting that out.
But, you apply one probe to one end of the fuse and the other probe to
the other end. It should read a very low value like 1 ohm. Both should
read the same if good. If bad, the fuses will most likely read infinite
resistance ie full scale or open circuit.
Testing a DC power bus from positive to negative, (ground), would also
be a case of looking for whatever resistance the output bleeder resistor
is across the DC bus, and not an open circuit, of infinity.
You have to have had the DC supply turned off long enough (some minutes)
to let the charges bleed off normally from the capacitors.
Don't ever measure ohms in an active circuit! It can burn out VOMs, and
may not be good on digital meters. See your specific manual on your
meter as to what is permitted.
Be sure to unplug equipment from power lines before testing with meters.
A switch should when closed (on), be no more than the 0.9 ohms or so, of
the shorted two test probes alone. At worst a few tenths of ohms. Best
is to compare a suspect switch to a similar on off switch. You may find
a similar switch on another equipment or from spares in your junk box.
Another reason to make up a junk box, to have spare or known good
components for comparison to tests on suspect components of the same type.
For learning more about testing, see the books by John Lenk. He has a
whole series on electronics repair.
Good Luck!
Stuart Rohre
K5KVH
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