[time-nuts] HP Z3805A GPSDO Oven Heater Voltages

John Stuart j.w.stuart at comcast.net
Wed Apr 23 03:37:06 UTC 2014

I have a HP Z3805A / 58503A with a cold outer oven. I have installed another
HP 10811-60165 DOXO, and then another power board.  Still, the outer oven is
not heating.
Heater resistance is ok at 19 ohm, but voltage on red wires to heater are
both at 5.0 VDC.  On another (good & warm) HP Z3805A, the red wire voltage
on P3-3 is at 15.27 V, so there is current flow through the heater and the
DOXO is nice and warm.
I found two other voltage differences on the power board terminals:
P2-8 Violet = 0.00 V vs. 4.5 on the good unit
P2-9 Green  = 8.14 V vs. 1.95 V on the good unit 
So, can someone tell me what the green and violet wires do that connect to
the main circuit board?  Any suggestions on how / what to troubleshoot next?
John Stuart, KM6QX
Lafayette, CA

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