Datron 1061A

[karoru]

Hello, dear EEV people:)

I've bought Datron 1061A meter that works a treat, but it looks like its battery hasn't been changed since 1985 (30 years lithium battery...). I want to replace it because I don't like having that ticking time bomb in my shiny boat anchor equipment. I've got 2 questions:

1. Is there a way to safely read the calibration constants from the instrument as a backup?
2. The battery is Li-SOCl2 1/2 AA that's soldered to the board, any ideas how to safely replace it? Solder new one in parallel and then remove the old one?

By the way, it was sold as 'broken' because it didn't give 0 V reading without probes connected...

[Gyro]

By the way, it was sold as 'broken' because it didn't give 0 V reading without probes connected...

That's because it has very high input resistance up to 20V - in the order of 10G Ohms (rather than 10M Ohm for the average DMM). Useful for not loading the circuit that it's measuring but it does mean that the reading will float (count up or down) due to its own input bias current (less than 50pA for the Datron) Perfectly normal for equipment of this type.

Edit: ...but you probably know that by now! 

[karoru]

Of course, but I don't think I was in position (or will) to explain that to the seller (who, looking at his auctions, deals with tons of obscure test gear on a daily basis, so he should know better)

[Gyro]

In terms of replacing the battery. You could PROBABLY get away with connecting a bench PSU set to the same voltage in parallel with the battery, including a series safety resistor (maybe 1-10k) for the duration of the change. Save time by snipping out the old battery and then cleaning out the PCB holes. Above all, make sure your solder joint is floating!  Either have the meter well insulated from the bench (and the bench PSU output floating) or maybe unplug the iron while making single joints.

Of course if you can find a way of backing up the CMOS data before-hand, it will be much safer.

[karoru]

Battery's actually soldered onto the free-standing resistor on one side (which is undocumented by the way, in the service manual with schematics battery with accompanying passives exists only on schematics, not on board assembly pictures nor BOM), so there's only one hole to clear;)

[radhaz]

A butane soldering iron is handy for that sort of work.
http://www.portasol.com/products_c.asp?C_ID=35

[ltz2000]

The battery is Li-SOCl2 1/2 AA that's soldered to the board, any ideas how to safely replace it? Solder new one in parallel and then remove the old one?

Just keep the meter powered while replacing the battery and your fingers away from the parts carrying mains / high voltage. Also make sure that your soldering iron tip is not grounded.

[karoru]

Just keep the meter powered while replacing the battery and your fingers away from the parts carrying mains / high voltage. Also make sure that your soldering iron tip is not grounded.

Thanks, I'll just use my UPS for powering the meter and do the replacement then:) I think it's the most brainfart-safe configuration in this case.

[Gyro]

Bear in mind though that there is potentially more risk of 'glitching' the CMOS RAM if the unit is powered - The CPU is running, data bus active, address decode logic powered. Just be careful where you drop your solder and take ESD precautions!

[jitter]

Is the assumption here that the calibration constants are in volatile memory?
According to page 33 of this document, those are actually stored in non-volatile memory, so swapping the lithium battery the safe way should not wipe those.