[R-390] Troubleshooting the R-390A Rf Module

[Roy Morgan]

On Mar 25, 2009, at 8:31 PM, DW Holtman wrote:

>
> Hello,
>
> I have an unusual problem.

The best kind!

> ... the 17 MHZ xtal oscillator V207 does
> not want to turn on. ... a tube extender ... it starts working.

Oscillators can be the most difficult circuits to make reliable when  
they are acting up.

> Does it
> want more/less inductance or capacitance?

Maybe more capacitance
(Pause to look at the schematic ... )

Notice C324 and C325.  They form a voltage divider and feed back path  
to make the thing oscillate.  One of those caps may be bad.

Also at pin 6 is the screen bypass cap C326, 5000 pf to ground.  An  
easy test for that one is to put a similar cap in parallel with it.   
You may be able to wind a parallel cap around the actual tube pin.

Of course if the cathode choke is mis behaving, that would cause  
trouble.  If  you can measure inductance a tube pin to ground test  
there would tell you if the choke is shorted.

Roy


Roy Morgan
k1lky at earthlink.net
529 Cobb St.
Groton NY, 13073