When I
switched the Titan from OPR back to SBY the attenuation
resolved, and happened every time I switched back to OPR.
The bypass RF path ( used for receiving and transmitting without the
amplifier ) goes through the normally closed contacts of the vacuum
relay. If the relay were mechanically stuck, or the contacts faulty, you
would have the problem both in OPERATE and STANDBY modes. The relay
being stuck may be the most likely cause of the fault, however not
mechanically stuck, but rather by "stuck" logic in the electronics that
drives the relay.
When I turned the radio on this morning everything was back
to normal. What is going on? A stuck relay someplace?
That suggests a part that is getting flaky. A capacitor getting leaky or
a transistor that is getting hot and going into thermal runaway. Off
tolerance resistors incorrectly biasing a transistor so that it always
stays on, or right on the edge of being on could do this.
The easiest way to mess up a Titan 425 control circuitry is to transmit
into it without a load on the output of the amplifier. Even with the
Titan turned off, this leaves nowhere for the transmit RF to be
dissipated, except in the components at the input of the 81219 Bias
Board. Check that board for toasted resistors.
DE N6KB
|