[time-nuts] PM6681 Counter Backup Battery

[Rex]

[This message is essentially a repost. See Note at bottom for details.]

The PM6681 counter (or CNT-81) has a small battery inside. It backs up, 
when the counter has no AC power, a section of SRAM memory. That memory 
holds a calibration constant that affects the accuracy of the counter's 
interpolation method for measurements. This memory also holds more 
mundane things like save and recall of counter user setups.

The battery should last for 5 to 10 years, but it is probably a good 
idea to replace it with a fresh battery every 5 years or so.

The backup battery is a single standard CR2032-style lithium 3V coin 
cell. To open the case there are 3 torx head screws. One in the bottom 
center (T10 size) and two at the back plastic feet (T20 size). With the 
screws our, I started the opening process by prying with a small 
screwdriver in the cracks between the plastic front panel and the case.

To keep the RAM memory intact, the counter must have AC applied and be 
in Standby. To remove the battery the holder has openings toward the 
front of the counter where you gently pry up the battery. I used a 
plastic screw driver adjustment tool. The new battery easily slides in 
the way the old one came out. For maximum long term goodness avoid 
touching the new cell with bare hands (possibly a bit too anal-retentive).

Hopefully a small pic I took of the battery location will be attached.

-Rex

[Note: I originally made this post as a reply to Bert in the thread 
"PM6681 PROMs v109". When I posted, I messed something up on the sending 
end which made the email look like it came from Bert ('ew') rather than 
from me (rexa).

This reposting is to fix that attribution and also to update the 
Subject, as this battery is unrelated to the PROMs.]



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