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

[Jon Schlegel]

Hello All,

Try taking a look at R207, the grid leak resistor.  The story I 
remember went something like
    "The radio only works when the VOM lead is on the grid of the XYZ 
tube" (from the days when 20,000 ohms/volt was King).


Regards,
Jon Schlegel WA3MVM


At 07:37 PM 3/25/2009 -0600, DW Holtman wrote:
>Joe,
>
>Thank you for the response. I swapped the tube with V401 from the xtal
>oscillator sub chassis, which is well used.
>
>Roy,
>
>I have been thinking about the same thing. I will next pull out the RF
>Module again and while it is out, change out C324, C324 and  C326. I have
>them on hand, and it will not be too tough. Also remove one end of L201 and
>check it. It is on a very low voltage circuit so an inductance check should
>work.
>
>Thanks for the help.
>
>Best,
>DW Holtman
>
>----- Original Message -----
>From: "Roy Morgan" <k1lky at earthlink.net>
>To: "r-390 reflector" <r-390 at mailman.qth.net>
>Sent: Wednesday, March 25, 2009 7:06 PM
>Subject: Re: [R-390] Troubleshooting the R-390A Rf Module
>
>
> >
> > 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
> >
> >
> >
> >
> >
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