[R-390] RF subchassis separation

[Roy Morgan]

On Mar 13, 2014, at 1:04 PM, Mark Richards <mark.richards at massmicro.com> wrote:

> Question A: As I keep hearing crystal replacement as the answer to this problem, can someone here lead me to a source?
> 
> I should probably replace the pair.  Test revealed that < 8MHz I have no radio.. so likely the other crystal gave up, too.

Before you order expensive crystals, make this simple test:

Hook the suspect crystal between the output of your signal generator and the RF probe on your VTVM.  Set a tenth of a volt output and low voltage range on the VTVM, and tune around the crystal frequency with the generator.  Slowly.  You’ll see a peak if the crystal is working.

You can make an RF detector with a diode, resistor and a cap if your meter doesn’t have an RF probe.

For the 200 kc crystal, you need a signal generator that goes that low.  The URM-25 is ideal.  *Some* audio generators go that high.

All of this is extra justification to have TWO (or more) R-390A’s, or at least spare small crystal ovens equipped with the right crystals.

Roy

Roy Morgan
RoyMorgan at alum.mit.edu
K1LKY Since 1958