Restoration/repair of my hp 3457A

[extremgear]

Hello,
i wanted to share with you the repair and preventive maintenance of my new meter, just in case it could help somebody else.
I bought this meter for 140E with a fault on it, self test resulted in "test failed" with an AUXerror 64 related to a Amps function error, after some test DCI didn't work, the only range working was the 1A range but with a huge 12% error...

What i did on this meter :
 - changed all the electrolytic caps ( they were good, but i had them ...)
 - changed the "Shafner" input filter
 - changed the battery BT501 ( save the cal data)
 - troubleshooted the Amps function error.
 - changed fuses (Front amp fuse was blown and mains input fuse was for the 120V market)

Replacement of the mains input filter:
the rivets of the original filter have to be drilled it is better to take apart the rear panel to do so.
the replacement part chosen from the same brand :FN9222-3-06 it is a bit longer than the original but it's ok.

Troubleshooting of the Amps function error:

After some search and measurement i found that the analog switch U403 was sending 5V to the input of U101 in Ma DC range, i took off this circuit and did some test on a breadboard and came to conclusion the IC was faulty, this circuit is not made anymore ( Intersil IL-390-5 ) but i was able to find a replacement part from vishay with the same characteristics :  DG390BDJ-E3
After IC replacement all range DCI are working fine .


Replacement of the Cal ram battery:

The original battery ( 36 years old) was reading 3,01V, i decided to change this battery.
i bought this model:  6237501301CR2/3AA Varta .
For the battery replacement some care have to be taken otherwise the meter will need a complete calibration.
I had to provide a temporary supply, i decided to connect the + of temporary supply to cathode of CR504 trough a 1n4148 diode and the - to the closest - of the original battery, but pay attention to this : there are several board revision and you must have a look to the service manual in order to know which board revision you have, on other board revision the name and location of the diode is different.

My meter now work pretty well, i tested it against a 34465A and it looks good but would need calibration or full performance test against trusty test gear to really know.
Have a nice day.

[AVGresponding]

Did you ever consider making a pluggable rechargeable battery mod? It's something I've thought about for my 3478A.

[Kleinstein]

With the relatively low power consumption there is no real need for rechargible. Chances are a rechargible cell will not outlast the old cell, even with only a few charge cycle.
A solution with 2 redundant cells would be nice, so like 2 x CR2032. Swap the batteries on every 2nd recal cycle would not be a problem and not add too much costs.

[extremgear]

Did you ever consider making a pluggable rechargeable battery mod? It's something I've thought about for my 3478A.

the original battery last for nearly 40 years ( i also have a 3478A with a battery that was still ok after 35 years) i think it's ok to change it every few decades .

With the relatively low power consumption there is no real need for rechargible. Chances are a rechargible cell will not outlast the old cell, even with only a few charge cycle.
A solution with 2 redundant cells would be nice, so like 2 x CR2032. Swap the batteries on every 2nd recal cycle would not be a problem and not add too much costs.

yes i was thinking about something like that, but replacing the battery with a temporary supply is not so hard .
and i think the next time i will have to do that is far away.