Jarl, OZ9MO Thank you for those two links! They have the information I needed, and are very well 'hidden' on the internet. I have had partial success. Per the work-around on www.realhamradio.com, I pulled P2-8 on the power board up to +5V, and the outer heater came on and is now being controlled by temperature controller on the power board; TP104 is modulating around 15.75 V. However the heater on/off control signal from the main circuit board (normally connected to P2-8) is still OFF at 0.0 V. For some reason (maybe firmware) the units CPU is not turning on this signal. I am thinking about permanently wiring +5V to P2-8 to keep the heater enabled. Why would the outer oven ever be turned OFF ?? Maybe to prevent over-temperature damage if the NTC sensor fails? When I bought this "HP Z3805A" from the Hong Kong seller a couple of years ago, it was advertised as having been upgraded to the features (firmware?) of the HP(Symmetricam) 58503A. Does anyone else have this 'model' and does the Double Oven XO keep the unit's top very warm, like it should? John Stuart, KM6QX Lafayette, CA _____
From: Jarl Risum [mailto:jarl.ri...@gmail.com] Sent: Wednesday, April 23, 2014 2:22 AM To: j.w.stu...@comcast.net Subject: HP Z3805A GPSDO Oven Heater Voltages Hi John You will find a comprehensive description of the outer oven heater circuit here: http://www.ko4bb.com/Manuals/05%29_GPS_Timing/Z3801/Z3801A_Outer_Oven/Web_Pa ge/Z3801A%20Outer%20Oven%20Controller.htm In my HP Z3805A the outer oven circuit is identical to the circuit in HP Z3801. A description of a Z3801A outer oven fault similar to the one you have can be found here: http://www.realhamradio.com/oven-confusion.htm You will also find a suggestion for a simple remedy. Good luck. Cheers from OZ9MO / Jarl in Denmark _______________________________________________ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.