Archive for February, 2022


Fluke 845AB repair

I was fortunate enough to find a 845AB on eBay that appeared to be in quite fine cosmetic shape. The Fluke 845 is a High Impedance Voltmeter with Null Detection so two voltage sources can be compared. A common use case for the nulling measurement is across Wheatstone bridge, whether a passive or active implementation. While this is an old analog meter movement instrument, they are a very nice addition to an electronics bench.

When I received the unit it was in fine shape and the battery pack had not yet leaked. All I had to replace was the line fuse and the 8 NiCD Sub C batteries. The batteries were readily available on Amazon and while I did not wish to stress the charging circuit, I went with Tenergy 2200mAh cells in replacement of the original 1800mAh cells.

Here is a picture of the original condition of the battery pack. As can be seen, there are several cells in there from Fluke that may have been original, but probably were replaced along the way at some point.

After replacing the cells, the unit indicated that it had adequate battery charge, and appears to be charging properly. Nice, clean repair.