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

[DW Holtman]

Hello,

I want to thank everyone for all of the help. While I had the RF Module out, 
I changed C234 and C235. Both of the caps tested good on a cap checker and 
showed infinite resistance while cranking 500 volts with a mega-ohmeter. 
Next, I removed R-207 and it read 113K instead of 120K, so it was replaced.

Put everything back together and it now works. I don't know what the problem 
was, but I was not going to change one piece at a time to find out.

Thanks again for all of the help.

Best,
DW Holtman


----- Original Message ----- 
From: "Jon Schlegel" <ews265 at rochester.rr.com>
To: <r-390 at mailman.qth.net>
Sent: Wednesday, March 25, 2009 8:38 PM
Subject: Re: [R-390] Troubleshooting the R-390A Rf Module


> 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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