[TenTec] Corsair Troubleshooting

[Stuart Rohre]

Alan,
Hum basically is a function of lack of DC filtering.  I would suspect a bad
capacitor of the electrolytics in the power supply.  Taking loose one end of
a capacitor, you see if there is current leakage if you complete the circuit
with a current meter.  A scope will show high ripple at the multiples of the
AC line riding on the DC of a bad capacitor.  You might have to take loose
more than one, one at a time to isolate the problem.  Use a resistor or lamp
to load the supply rather than the rig during such tests.  The resistor has
to be a power one, of course, rated to draw the current the rig uses at
least in receive.

The hum could also be a manifestation of RF getting back into the power
supply.  That might go with the rig tripping off when loading is increased,
but that also could be an open filter, or a leaky filter capacitor.  You
need to get the DC supply clean first.  Verify that this is only in the
power supply by running the rig off a car battery for a test.  If you can
load to full power there, then it is a power supply fault.  Transistors do
not get "weak".  They fail either open or shorted.  Now if there is an SCR
device in the crowbar, that might be turning on part way, limiting the
current you can draw to the rig.  Again, for a test, use a load other than
the rig like a lamp that will draw the same current, and see if the power
supply will deliver it if the crowbar circuit is temporarily opened up,
(disconnected from the plus side of the bus).  Depending on age of the
supply, if 10 years old, the capacitors, (electrolytic) are the first
suspects.  A change of resistor value "might" have caused the crowbar point
to change, look also for any overheated component.

Of course, a breaker can age and the spring could be weak causing premature
tripping.  If a substitute is available, this should also be a check you do.

GL and 73,
Stuart K5KVH



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