[time-nuts] HP 5328A fan - suspected issue

paul swed paulswedb at gmail.com
Fri Jan 17 21:00:55 EST 2014


Brett
Welcome to the group. If you do not have a pdf of the 5328 manual go here
to get a copy.
http://www.ko4bb.com/manuals/index.php
I had several 5328s a long time ago and they are quite nice counters.
Looking at the schematic there is indeed a tstat that controls a SCR that
runs the fan. Now its not clear to me what resistor might be smoking. There
is a .47 ohm resistor for current sensing. If thats smoking you have a
short or something.
But thats speculation. Take a look at the schematic and let us know what R
is smoking. That may help us a lot.
To the fan 12 vdc or such it could work but they may draw a fair amount of
current and do generate noise that may possibly effect low level readings.
So certainly can work.
Regards
Paul
WB8TSL/1


On Fri, Jan 17, 2014 at 6:03 PM, Brett Owen Rees <breree at gmail.com> wrote:

> Hi all,
>
> This is my first post to this list. I recently acquired three HP 5328A
> counters and have been using one in my shack. They all seem to have fan
> issues, with the fans not running in two of them and in the third unit a
> resistor near the fan starts to smoke if I turn it on. All of the fans look
> identical, being 110V AC units.
>
> So, I have some questions:
> - should the fan run all of the time or is it on a thermostat
> - does the smoking resistor mean that the fan is seized
> - can I replace it with a 5V/12V computer fan. If so, can I safely tap DC
> off the power supply and will the fan introduce any electrical noise? I am
> 240V here so sourcing a fan 110V fan locally may be difficult
>
> The counter I have running seems ok without the fan running. It is the pick
> of the bunch with the OCXO, 525MHz and DVM option. Being the best
> oscillator I have currently, I have checked it against WWV and it seems ok.
> I also used it as an alignment  reference for a funcube dongle receiver
> (with tcxo) and am receiving WSPR spots on frequency, so I think it is
> good. I am slowly getting the time-nuts bug and am building a GPSDO with a
> Morion MV89A ocxo ...
>
> Many Thanks es 73
> Brett VK6EZ
>
>
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