[R-390] Intermittent Calibrator Signal !

[Larry H]

Hi Rick,  You can easily determine if this problem is 1 or both oscillators - The bfo should work on any received signal or cal marker.  
The cal markers can fade away if the cal osc or cal multivibrator is malfunctioning.  The easiest check is looking at the carrier level while tuned to a cal marker, you should have between 10 and 40 db in agc mode if the rx is working properly.  When the cal signal fades away, if the rx signal sensitivity is still good on signals from the antenna, then its the marker generator.  Sometimes the multivib gets flakey because the plate resistors get damaged or the caps c312 through c315 go bad.  I'd start with scoping the cal osc output at pins 2/7 on the v206 socket with that tube out.  You should see 200kc sig at @ .5vac.  Then if ok, it's probably the multivib.  With pwr off, measure resistance between pins 1 & 6 on v206 - it should be @ 20k ohms.  Or you can scope the multivib out at pin 7 on v205 using an extender.  Then there's the cathode follower could be bad - check with res or voltage measurements.  This assuming the 1pf output cap is good.
Good luck and let us know what you find.
Regards, Larry

      From: Rick Roxx via R-390 <r-390 at mailman.qth.net>
 To: "r-390 at mailman.qth.net" <r-390 at mailman.qth.net> 
 Sent: Wednesday, February 22, 2017 4:15 PM
 Subject: [R-390] Intermittent Calibrator Signal !
   
I’m having an issue with a R-390A I'm working on - TheBFO/ calibrator signal is random - sometimes it's there, other times it's not andsometime it's there and then just fades away. Any suggestions on the best place to start digging ??  Thanks ! Rick Popovich
______________________________________________________________
R-390 mailing list
Home: http://mailman.qth.net/mailman/listinfo/r-390
Help: http://mailman.qth.net/mmfaq.htm
Post: mailto:R-390 at mailman.qth.net

This list hosted by: http://www.qsl.net
Please help support this email list: http://www.qsl.net/donate.html