Hewlett Packard 3457A Multimeter

Minor upgrades, main­te­nance, and cleanup of a Hewlett Packard HP 3457A dig­i­tal multimeter.

I pur­chased this HP 3457A mul­ti­me­ter as an untest­ed unit that pow­ers-up. Luckily when it arrived it turned on and had no errors after per­form­ing all the self-tests.
It was not in the best con­di­tion and very dirty with lots of adhe­sive residue. It was also miss­ing it’s pow­er but­ton.
I was able to 3D print a replace­ment pow­er but­ton, and then spent sev­er­al hours dis­as­sem­bling and clean­ing the unit.

Part of the pre­ven­ta­tive main­te­nance that I want­ed to per­form was replac­ing the IEC C14 AC pow­er input mod­ule. I was able to find a Schurter 3–130-953 sin­gle stage IEC fil­ter that was just a bit longer in length to replace the orig­i­nal unit.

For the most part the boards were in very good con­di­tion with the excep­tion of the main ana­log board. 

Someone had worked on the ana­log boards relays in the past and did­n’t both­er to cleanup after their repair or what­ev­er they were doing. The relays affect­ed were the front / rear input switch­ing cir­cuits. I spent anoth­er cou­ple of hours re-sol­der­ing the con­nec­tions and clean­ing off all the flux around all the relays then clean­ing all the high imped­ance sig­nal areas of the board, because there was no telling how the board had been han­dled in the past.

The next item was a small upgrade to the ref­er­ence mod­ule which involved adding addi­tion­al insu­la­tion to the LM339 Zener ref­er­ence. I used my favorite Rova flex plus Aerogel insu­la­tion tape to add sev­er­al addi­tion­al lay­ers of insu­la­tion to the orig­i­nal hous­ing. This increas­es the ther­mal sta­bil­i­ty of the ref­er­ence. I also thor­ough­ly cleaned the con­nec­tions of the ref­er­ence board then used a small amount of DeoxIT Gold on the pins.

The four elec­trolyt­ic capac­i­tors on the dig­i­tal and ana­log boards pow­er sup­ply sec­tion were replaced with 10000 Hrs @ 105°C rat­ed Nichicon and Rubycon units.
Also added was a com­mon mode fer­rite choke that was slipped over the cable between the trans­former and ana­log board pow­er sup­ply sec­tion.
The mem­o­ry back­up bat­tery was also replaced with a Panasonic BR‑2/3AE5SPN unit.
In the future I may try the Ferroelectric ram replace­ment, but for now this new bat­tery should last quite a while.

The case was miss­ing two of it’s feet so I 3D print­ed a new pair and some TPU inserts to replace them. Not quite as nice as the orig­i­nals but they worked very well.

While ful­ly func­tion­al, the LCD dis­play is not the eas­i­est to read and is start­ing to show some degra­da­tion on the low­er edge of the screen. There are some OLED screen replace­ments solu­tions out there, but for now the LCD screen meets my needs.

After reassem­bling the unit amaz­ing­ly every­thing still worked.
When com­par­ing this mod­el to my HP 3456A, this mod­el adds some addi­tion­al capa­bil­i­ties such as DC and AC cur­rent mea­sure­ments along with a basic fre­quen­cy mea­sure­ment func­tion. It also excels when mea­sur­ing low­er range DC volt­ages, but falls short when mea­sur­ing AC volt­ages com­pared to the 3456A volt­meter.
So far I am very hap­py with this addi­tion to the work bench.