[TenTec] Is my Titan 425 broken?

[Ken Brown]

> 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