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Re: [TenTec] Eagle problem?

To: k9yc@arrl.net, Discussion of Ten-Tec Equipment <tentec@contesting.com>
Subject: Re: [TenTec] Eagle problem?
From: Stuart Rohre <rohre@arlut.utexas.edu>
Reply-to: Discussion of Ten-Tec Equipment <tentec@contesting.com>
Date: Fri, 16 May 2014 18:04:54 -0500
List-post: <tentec@contesting.com">mailto:tentec@contesting.com>
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
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