[time-nuts] Fwd: HP 53131A Power Off Mod

Wayne Holder wayne.holder at gmail.com
Sun Jun 3 18:11:17 EDT 2018

*Important Update:* due to a mistake in my thinking, I had to upgrade the
fuse I added to a 220V, 3A model to match the fuses on the internal
switching power supply.  My original plans were to mount the fuse on the
power supply PCB and use it only to fuse the small power adapter used to
power the relay.  But, when there was not enough space, I decided to use
the in-line fuse adapter, instead.  Completely overlooking the fact that
the in-line fuse would then need to handle the full power load.

The project page at
https://sites.google.com/site/wayneholder/hp-53131a-power-off-mod has been
updated accordingly.  Sorry for the mistake and I hope this hasn't
inconvenienced anyone.


On Fri, May 18, 2018 at 4:56 PM, Wayne Holder <wayne.holder at gmail.com>

> The PCBs and Parts arrived and, after putting everything together and
> testing it, it all seems to work fine.  And, to document everything, I've
> put up a web page at my web site that describes the mod and how to
> implement it:
>   https://sites.google.com/site/wayneholder/hp-53131a-power-off-mod
> I had two spare board sets left.  One is claimed, but if someone would
> like the other set, send me your address and I'll send them your way.
> Wayne
> On Mon, May 7, 2018 at 10:27 PM, Tim Tuck <timt at skybase.net> wrote:
>> Hi Wayne,
>> Congrats on a nice simple mod !
>> I have both a 53131 and 181 in need of these :)
>> Can you share the gerbers for your PCBs and then I can cut them out on my
>> mill.
>> I could probably make a few for any interested Australians, to save on
>> cross pond postage.
>> thanks
>> Tim
>> On 8/05/2018 9:08 AM, Wayne Holder wrote:
>>> I recently purchased a surplus HP 53131A and was surprised to see that
>>> it's
>>> designed to stay partially powered on, with the fan running, even when
>>> the
>>> power switch is in standby.  The manual says this is for timebase
>>> temperature stability but, since I plan to use with my Trimble
>>> Thunderbolt
>>> as the reference source, I don't really need this feature.  So, I decided
>>> to see if I could change this.
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