Along all our equipment we have a portable oscilloscope and DMM (fluke names this Scopemeter) Fluke 123, which is kind of old unit, but very useful for on-the-field troubleshooting and, as many report, already undistructable piece of equipment. However, this (otherwise excelent piece of equipment 😉 ) has some drawnbacks.

Originally it is powered using 4 NiMH batteries which have quite short battery life and plenty of self discharge, which practically means that device shall be charged every time before using (if not using it every day).

There were other guys on EEVblog, already trying to fix this issue with lithium batteries. As originally F123 uses 4 NiMH cells (4,8 V nominal, 6 V fully charged, CC charging method), there are some changes required to power it from lithium cells (7,4 V nominal, 8,4 V fully charged, CC/CV charging method):

  • Increasing charging current from 400 mA to approx. 800 mA for faster charging
  • Change charging voltage to 8,4 V (originally around 6 V)
  • Change resistor divider in a way that battery icon will display proper battery state with new voltage levels

Schematics (click to enlarge) where mods are displayed with red (yellow: components that are modified):


Another big problem with this Scopemeter is low display brightness which gets even worse after time, as display backlight is done using CCFL lamp which intensity drops after some time.

A good news is, that this lamp can be quite simply replaced with a LED strip, which is widely avalible and way more powerful then original lamp. To power the LED strip an additional DC-DC step up converter is required as most LED strips is made for 12 VDC. Additionally a power-on logic has to be made in a way that LED strip is turned on when Scopemeter is powered on.

You can find how both mods are apllied on a F123 in the gallery bellow. There are comments by each image, describing the procedure.

(I probably don’t need to mention, that you are doing it on your own responsibility … You need some electronics skills for this, but as you owe this piece of equipment I assume you do have some …)

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