Replacement for a Fluke battery indicator (731 and others) - Page 1
Forum section: electronics / general

author: dj831
author_rank: Regular Contributor
timestamp: October 20, 2020, 03:12:48 pm
content: Good day everybody,I'm searching for a way to replace a battery indicator for a Fluke 731B. Such a 731B galvanometer is used also in a 731A, 510A and 515 (perhaps with different ranges and layouts, I'haven't checked). This is a Mura ammeter, 1mA, TS10.No way to repair it, since winding is openDoes someone has an idea on how to find such a part made from unobtainum, or any idea on how to replace it?Thanks!

author: Andreas
author_rank: Super Contributor
timestamp: October 20, 2020, 06:06:35 pm
content: Hello,I would probably put a LED behind the old meter controlled by a battery monitor cirquit like in my AD587LW reference.https://www.eevblog.com/forum/metrology/ad587lw-10v-precision-travel-standard/msg1449488/#msg1449488https://www.eevblog.com/forum/metrology/ad587lw-10v-precision-travel-standard/?action=dlattach;attach=402886average current consumption is 10-20 uASlow flashing (all 2 Seconds indicates low battery)Fast flashing (every 1 Second indicates level ok)with best regardsAndreas

author: dj831
author_rank: Regular Contributor
timestamp: October 22, 2020, 08:51:15 pm
content: SuccessAndreas, very good idea, the blinking LED, I keep it in mind for a future design. And thanks for taking time to answerIssue was a desoldered spiral, breaking the circuit. I was not able to resolder it, since it was desoldered on the bottom of moving part. I cannibalized an old galvanometer found a day in our municipal recycling center (sure, people are not supposed/allowed to retrieve things from there, but we have very nice guys). It was a vu meter, by far much bigger than the one found in the 731, and having its own scale drawn by previous user on a glued sheet of paper.After a quick look at the rear, it became pretty obvious that these vu meters are almost all the same, with different layouts, of course. I removed that meter from its body, pushed it in the body of the one used in the Fluke, and taadaa, perfect fit!Obviously, the needle was way longer than the one of the Fluke. I cut it with a flat blade wire cutter (a TR-30 from Pergiacomi), result is perfect. If this was a metrological meter, I would have balanced on all three axes, but since it is used only vertically and just an indicator, I was happy with that, moving the zero up to the small black dot at the bottom left - I remember the huge amount of time spent with wax and soldering iron to balance Monoc and Metrix meters.For those interested, original meter is 1mA and has an internal resistance of 100R. Since my meter had a full range of 500µA and an inner resistance of 520R, I added a chain of 3 resistors to have 520R paralleled, thus having a full range of 1mA. Note that resistors cannot be soldered straight between pins of the meter, since there is a piece of metal pushing the rear of the meter to hold it in its place. The difference of total resistance (260R instread of 100R) is negligible. I think that reason for that desolder could be due to dead batteries: when powering unit on or off, needle goes on each side in a very brutal way. That does not happens with charged batteries (I used a pair 7,2V Eneloop assembled batteries).The only difference is the color of the needle: black instead of red.Meanwhile, an eevblog member proposed me via PM to sell me an old meter from his dead Fluke 730A, let's see if I receive it.