Seeking some idea here as to what happened in the Voltage trim concept in the 5345A
I have been nursing two 5345As over the last few years. I kind of took it on faith that HP tied off the varactor trim Voltage line as there appears that they did not make a method to tickle this Voltage on either the 5345A with the 10811A or with the 10544A. One of the 5345As died and had to be solved. The problem was that its 10544A had died. The rock is bad on that one. However, since my desire is to add the Voltage trim adjust circuit that HP appears not to have installed I made some inspection of pins 5,6, and 7. It appears that the important item is pin 6 and it is floating in the 5345A. What gives? The 10544A schematic that I have shows minus EFC in as pin 6 and option for pin7 or internal 6.4 V for EFC plus. Inside the 10544A that I have, pin 6 has a wire to the prescribed 20k resistor and the varactor is installed. pin 7 is not connected. The second 5345A that I have been running has a 10811A in it and the 10811A schematic shows EFC to pin 6 (varactor anode) and varactor cathode to internal reference at 6.4V same as the 10544A that I have. Is it possible that HP just let pin 6 float in the 5345A assuming that the 10544As were to be installed without the varactor option? The nature of a floating anode is such that the diode goes into a very undesirable region, low Q high capacitance. Complete troubleville. The floating nature of this internal pin means that I need to restart all of my tuning an observations on these units. Unless I am missing something here? My idea is to make a Voltage reference onto one of the little removable option covers on the back with a pot to eliminate the cats breath tweaks to the trim cap in the 10811A and to finally nail the zero. Ha anybody been down this path before? Any suggestions? Any voices from the distant past of HP engineering? Regards; Greg _______________________________________________ time-nuts mailing list -- [email protected] To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
