[1000mp] Re: 1000mp digest, Vol 4 #207 - 4 msgs

[Dick Carroll;]

>  George W5YR wrote

> Sound like the transistor is just a simple switch for the relay. When the
> relay should be on, the base should be at an appropriate voltage for the
> circuit in order to turn the transistor on. If the base is being switched by
> the T/R logic and the relay doesn't come on, that pretty well points to the
> transistor as being defective - replace it. If no base voltage change is
> observed, then start working backwards through the T/R logic from there.
>
> I wouldn't want to argue about it, but a curve tracer to evaluate the
> transistor is a little overkill. It either switches or it doesn't.

All very true, George, but using a curve tracer will allow sometimes you to do
troubleshooting without powering up the rig or removing any components. You can often get
a good idea of the status of a PN junction device quickly and easily.

  I have a bit of trouble these days, (what with a bit of arthiritis in the hands and
eyesight that doesn't work near as well as it used to)
with probing live solid state circuits with VOM probes-one slip and you can easily "fix"
it good!
 Of course one has to be careful where you use a curve tracer since it does introduce
voltage into the circuit under test, and can thus destroy junctions under the wrong
circumstnces. One needs to evaluate the circuit first.

73, Dick W0EX