[time-nuts] Re: Z3801A questions

[Joseph Gwinn]

Re: time-nuts Digest, Vol 229, Issue 21
On Sat, 20 May 2023 03:30:25 -0400, time-nuts-request at lists.febo.com 
wrote:
> 
> 
> ----------------------------------------------------------------------
> 
> Message: 1
> Date: Fri, 19 May 2023 20:17:49 -0500
> From: Mahlon Haunschild <k4oq.radio at gmail.com>
> Subject: [time-nuts] Z3801A questions
> To: time-nuts at lists.febo.com
> Message-ID: <1D775F50-375D-48AB-A340-79A5E3906A45 at gmail.com>
> Content-Type: text/plain;       charset=utf-8
> 
> Hello list.  Just joined and, after reading the list archives, I 
> feel that I Am Not Worthy to ask these questions, but here goes.
> 
> I’ve had a Z3801A just sitting around for years now and, the other 
> day, I finally decided to experiment with it a bit.  I already had 
> a 26dB Andrew antenna and a Vicor 48V 2.9A power supply for it, so 
> I put the antenna on the back of the receiver with some N adapters, 
> wired up a serial cable to an ancient ThinkPad running SatStat, 
> placed the whole rig in the back yard, and turned everything on.
> 
> To my astonishment, after placing it into survey mode, four hours 
> later, it had completed its sky search and had switched over into 
> position hold, with a  TFOM of 3 and a FFOM of 0.  Since all I 
> wanted it for was to use as a freq reference, I thought it was good 
> to go.
> 
> The next day I tried it again.  No go.  The Z3801A acted like it 
> had developed an internal power supply short because it was causing 
> the Vicor to go into current limiting, with zero volt output.
> 
> I’ve read the material on 56V vs 48V switching supply startup for 
> these, and I will them that next.  Failing that, I’ll troubleshoot 
> the power supply.
> 
> It appears that a long time ago someone reverse-engineered the 
> power supply design and published a schematic for it, and Google 
> found it somewhere in https://xdevs.com/doc/HP_Agilent_Keysight/ 
> <https://xdevs.com/doc/HP_Agilent_Keysight/> but is it on the web 
> elsewhere?
> 
> If all else fails I’m tempted to yank the two DC-DC converters from 
> the power supply board and power the whole thing with a suitable 
> AC-DC triple-output switcher (specifically, a Nemic Lambda 
> LWT-50H-5FF, which is on hand).  Has anyone done this?
> 
> Lastly, I’m considering trying an Oncore UT+ instead of the VP to 
> get its better front-end filtering.  Opinions?

I'd bet that at least one electrolytic capacitor de-formed while the 
unit was on the shelf, and then failed when power was re-applied 
after all those years.  So look at all electros, and replace any that 
seem off.  

Joe Gwinn