[R-390] Capacitor Tester

[Jim]

A Non-Contact Laser Thermometer is a useful tool and MUCH safer than the 
"finger test"
around HV circuits.

Jim

B+ Bypass Capacitors:  As noted above, these
typically begin to leak and then get more and
more leaky.  As they draw more and more leakage
current, they run hotter and hotter, often
splitting their plastic encapsulation
open.  However, they can be quite leaky and not
cause obvious symptoms.  They do put a greater
strain on the power supply, by drawing more
current than normal, so it is well to find them
and replace them.  So look first, for obvious
physical damage (split cases, etc.).  Another
good diagnostic tool is your fingers -- bypass
capacitors should NEVER run warm -- any bypass
cap than runs warm from internal heating (as
opposed to being heated by nearby resistors,
chassis, etc.) should be replaced.  (Be careful
to avoid nearby high voltage.  Reach in with only
one hand, and keep the other hand and all other
body parts out of contact with any part of the
radio.)  Look also at the resistors that feed B+
from the main supply to each bypass
capacitor.  If any of these resistors appears to
have been running hot, the associated bypass cap should be checked 
carefully.