[time-nuts] HP 58503A failure

Stan swperk at earthlink.net
Fri Nov 4 21:18:36 EDT 2016

I have had an HP 58503A GPSDO with the Option 001 display running
continuously for over ten years without a problem-that is, until today. When
I looked at it this morning, the display was showing a valid time, but it
was frozen and not advancing. Pushing on the buttons had no effect. I
unplugged it, let it rest for a minute or so, and plugged it in again, and
this time the display lit up with a string of several identical "garbage"
characters that extended only part way across the display. The rest of the
display was blank. Pushing on the front panel buttons had no effect, the
display at one point changed to a different string of meaningless characters
and, needless to say, the clock never resumed running. 


Unplugging it and plugging it in again resulted in the same behavior,
although different "garbage" characters were displayed, including some of
the annunciators in the VFD that are just 53131A and 53132A counter
functions (+WID, -WID, GATE, etc.). I opened it up and checked the power
supplies, and they were spot on (+5 VDC, +15 VDC, and -15 VDC) with no
measurable ripple. I also checked to see if I could communicate with it
through the serial port using GPSCom (which has worked fine in the past),
but no luck. I just got "Receiver Timeout" error messages. The power LED
glows steady green, but no other LEDs light, even when the buttons are


I'm not sure if a service manual or CLIP even exists, but I certainly
couldn't locate any service info whatsoever. Any ideas?




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