[TenTec] Eagle problem?

[Stuart Rohre]

Jim, don't we all use Flukes now?  :-)  I do have several at home and 
work.  I was remembering a discussion of a rig fault where the pin 
intended for grounding, had not been grounded at the radio connector 
entry to chassis.

Good point you make about low ranges needed for ohms measuring.  There 
are some good build it yourself low ohms measuring circuits out there, 
to extend the range of an ordinary meter.  The Graf (author) series of 
circuit diagrams books includes at least one.  The ham magazines in last 
40 years had one or more.

In the midst of measuring things, most good troubleshooting includes a 
thorough visual inspection to see how things are bonded and grounded, 
and if the circuit board is providing the connection to chassis.
Unfortunately, we had not done a pre service inspection of the following 
radio incident:

For high current faults, we have seen a Yaesu 5100 that had RF 
connection to circuit board and its DC negative power line to same 
circuit board at other end of chassis.  A lightning event on the tower 
induced shield current down the coax to the radio , across the circuit 
board, vaporizing part of the ground copper, and then to the DC negative 
line which returned to AC third pin and power supply chassis.

The bonding was done by an experienced power plant engineer, but it 
provided an extra return path through that circuit board trace, that 
caused severe damage to the trace.  Luckily, that radio has survived 
that, with a bus bar now bonding DC negative to the coax connector shell 
external to the chassis.  (No longer relying on the radio circuit board 
traces.)  The radio worked even after losing part of the board copper, 
but only if the coax was connected, which was grounded to the tower and 
earth providing a return through the AC third pin.  That observation 
prompted us to open the radio, which then showed the missing trace.

As for braid failures, literature about high current faults has stated 
that braid can blow apart in a near direct strike, as little shards of 
wire.  Indoors in someone's shack that could cause injury, or put small 
shorts into places hard to find.

Copper flashing could be used in place of braid.  The use or either was 
to provide low inductance through wide flat conductors used for bonding 
equipment together.

Stuart Rohre
K5KVH