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. But, unlike how Gary Sweeney accomplished this, <https://www.youtube.com/watch?v=xyFBBYZ6jXI&t=271s> I wanted a mod that I could easily undo and which wouldn't require me to hack up the existing power switch. After looking over the schematic, I determined that the power/standby switch is DPDT switch that's used only to enable +12 volt and -12 volt DC power by pulling two control lines to ground. The actual power supply is wired directly to the AC entry connector. The signal lines from the switch enter the main board via a 26 pin ribbon cable on pins 17 and 19. So, I designed a simple PCB that breaks out these connections (and ground) to a separate, 3 pin connector and then hard wires the +/- 12 volt enable lines to ground. The connector on top is intended to plug into the ribbon header connector on the main board and the connector on the end of ribbon cable then plugs into the lower connector. I also designed another PCB that's going to mount inside the 53131A using 3, 3mm holes located in the rear of the unit near where the 26 pin ribbon cable connects to the main board using nylon standoffs. This board will contain a small, 12 volt encapsulated AC power supply module, a relay and a pluggable connector where the AC lines will come and go. The Mean Well IRM-01-12 power supply module I selected has a no load power consumption <0.075W, so I think that's about as close as you get to a true "off" switch without making a more invasive mod like Sweeney's. The overall design is shown in the following schematic: I'm waiting to get the PCBs back from OSH Park so, if anyone is interested in implementing my approach in their 53131A, stay tuned and I'll let you know how this all turns out. BTW, the parts count (excluding the PCBs) is about $17. The switch breakout PCB costs $7.50 (for 3 copies of the board) at OSH Park and an additional $15 for the power supply/relay board. But, one could easily build these on .1 inch perfboard to save a few bucks. Or, if I don't screw anything up, I'd be happy to pass on one of my 2 spare PCBs to anyone interested. Wayne

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. --- This email has been checked for viruses by Avast antivirus software. https://www.avast.com/antivirus

Thanks! I plan to publish the Gerber files and make them available to fab at OSH Park as part of an a article I'll put up on my webpage at https://sites.google.com/site/wayneholder/ but I want to make sure everything works as expected before I do. I'm still waiting for parts and the PCBs to show up and I want to make sure every things works safely, as AC voltages are involved. So, it make take a week, or two before I'll know if I need to fix anything, or redo one of the PCBs. Wayne On Mon, May 7, 2018 at 10:27 PM, Tim Tuck <timt@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. >> > > > --- > This email has been checked for viruses by Avast antivirus software. > https://www.avast.com/antivirus > > _______________________________________________ > time-nuts mailing list -- time-nuts@febo.com > To unsubscribe, go to https://www.febo.com/cgi-bin/m > ailman/listinfo/time-nuts > and follow the instructions there. >

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@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. >> > > > --- > This email has been checked for viruses by Avast antivirus software. > https://www.avast.com/antivirus > > _______________________________________________ > time-nuts mailing list -- time-nuts@febo.com > To unsubscribe, go to https://www.febo.com/cgi-bin/m > ailman/listinfo/time-nuts > and follow the instructions there. >

*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. *Wayne* On Fri, May 18, 2018 at 4:56 PM, Wayne Holder <wayne.holder@gmail.com> wrote: > 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@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. >>> >> >> >> --- >> This email has been checked for viruses by Avast antivirus software. >> https://www.avast.com/antivirus >> >> _______________________________________________ >> time-nuts mailing list -- time-nuts@febo.com >> To unsubscribe, go to https://www.febo.com/cgi-bin/m >> ailman/listinfo/time-nuts >> and follow the instructions there. >> > >