Amateur radio, programming, electronics and other musings

MFJ-269B Battery Upgrade

MFJ-269B Battery Upgrade

I’ve had an MFJ-269B for many years.  It is a useful tool to have when building and testing antennas prior to putting them into service.  It runs from 12v and allows you to fill it with 10AA batteries.  I filled it with 3000mAh batteries.  The problem I found was it always seemed like the analyser was out of charge.  The analyser contains a charge circuit and if the jumper is in the “charge” position the batteries are charged when plugged into an external 12v source.

Looking at the schematic it shows that the charge circuit is only capable of providing 69mA at best.  I’ve heard others indicated it could be as low as 20mA.   This means the charge time could be anywhere from 2-7 days!  Not useful at all.

I decided to pull out the batteries and replace with a LiPo battery.  I took some measurements of the available space and went hunting for a suitable battery from HobbyKing.  Once the battery arrived I took some photos of the mods to share here.

The process was as simple as this….

  1. Remove the rear casing (8 screws)
  2. Remove the battery holder (2 screws)
  3. Snip the wire off of the battery holder and terminate it with either a JST or PowerPole.  I use PowerPoles on EVERYTHING.
  4. Cut some cardboard to provide some insulation between the battery and the PCB.  It will also ensure that anything sharp won’t pierce the battery.
  5. Ensure that the “charge” jumper is not enabled.
  6. Ensure the battery is fully charged.
  7. Mate the two power connectors
  8. Place the battery into the analyser
  9. Replace the back cover
  10. Check the analyser is still working.

I may install a panel mount PowerPole and balance cable so that I don’t have to remove the back cover to charge the battery.  The LiPo lasts far longer than the batteries and can be charged extremely quickly when it does go flat.