HP’s 34970A Data Acquisition / Data Logger Switch Unit is part of HP’s (then Agilent’s and now Keysight’s) data acquisition ecosystem. A seemingly common issue with this device is that if its internal battery dies, the entire machine will fail to power on. I was able to revive this particular unit by replacing the battery.
Opening the 34970A
Unscrew the 2x T4 Torx screws on the back of the unit, then remove the rear bumper assembly. Next, unscrew the T4 Torx screw on the underside of the unit and slide the case off of the unit.
At this point, I measured the battery voltage. It read 0V, confirming that it needed replacing.
If continuing with the battery replacement, unscrew the T4 Torx screw holding down the upper 34970-66504 DMM card, then rotate the board out of the way, exposing the battery.
Replacing the Battery
With the DMM board held out of the way and the battery exposed, it is now possible to desolder the battery. The technique I used was to first introduce a bit of leaded solder and flux, to make the existing solder flow more nicely. Then, I used a solder sucker (Engineer SS-02) to remove as much of the solder as possible. After that, I worked on the single-pin battery terminal, pulling that end of the battery up slightly while keeping the soldering iron on the terminal.
From here, I cycled through all the pins with the iron, pulling the battery out further and further each time, until each pin was free from the PCB.
After removing the old battery, I cleaned up the flux with isopropyl. Supposedly these batteries can leak, damaging nearby traces. Fortunately the traces looked good in this case.
Now the new CR14250SE battery can be inserted and soldered in place. The CR14250SE-FT is available at Digikey and is drop-in compatible.
Closing the 34970A
The 34970A can be closed back up by performing the opening steps in reverse.
Power-On and Test
With the battery replaced, this 34970A turned on immediately once I plugged it in and pressed the power button. My new concern was the ERROR indicator on the display. I was able to read one of the two errors (204) but they were both cleared before I could read the second error. Fortunately, Keysight documents that benign errors 201, 202, 203, and 204 may be thrown when the internal battery is discharged or replaced. They simply indicate that the “instrument’s storage status information, date and time and other system-related information” were lost due to lack of battery power. Notably, the important calibration data is stored in FRAM, so is not affected by the dead battery.
I also performed a SELF test by powering off the unit, then holding the SHIFT button while powering on, continuing to hold the SHIFT button until the machine beeped and entered SELF test mode. This test passed, providing some confidence that the device is operating properly.
