[R-390] 3MC issue updated

[Flowertime01 at wmconnect.com]

Steve,

I second what Don had to say.

It sounds as if the crystal is falling out of oscillation.

E204 is the grid of the second crystal oscillator test point.
With a signal generator and an isolation cap, inject 23 MHz at a low level 
into the grid test point. As you rock the generator through the exact 
frequency you should be able to force the crystal back into oscillation and the 
band should come alive.

This will be your clue that the crystal is just not up to par for the 
R390/A circuit.

Lots of times we see the crystal oscillate on the fundamental rather than 
the second harmonic. 

We also see the crystal is oscillating but off frequency. You switch over 
to 3 or 20 and the crystal starts at more than one frequency (first, second, 
third, fundamental spur). After 30 seconds if gets a little warmer and the 
needed frequency is squeezed out as the wrong frequency spur takes over. So 
they test good in a tester. But unless you have a tuned circuit (for load) 
and counter on them you do not know where they are oscillating. As Dan pointed 
out the testers are also more robust so they will put marginal crystals 
into oscillation.

Nothing real scared about the R390/A crystals. They have a series which is 
the temperature range. Several different series all have the same can / pin 
size. You do want a 11.5 second harmonic for the 3 and 20 Mhz bands. If you 
do not have a crystal on hand you mite as well order the real thing as to 
mess around with a wrong temperature part.  Ask for one on the reflector here 
and see what offers you get. Old parts are likely to last just as long as 
some new part. Its a rock already millions of years old.

Roger AI4NI</HTML>