The well-known Maha-Powerex battery charger/analyzer MH-C9000 has many nice features, and is appreciated by many people who bought it and has been using it for years.
However, the LCD backlit of this analyzer is always on when one or more batteries are processed, no way to dim it or turn it off; the backlit is so bright that it can be annoying in some circumstances, e.g. in a bedroom in the night.
The purpose of this instructable is to show how this battery charger/analyzer can be enhanced with a feature which has not been provided by its designers: the LCD backlit on/off switch.
WARNING: applying the procedure described below, the warranty of your MH-C9000 battery charger/analyzer will be voided, if already valid, therefore make it at your own risk!
Step 1: Open the Charger Case
First of all, remove, with a small screwdriver, the four small adhesive pads at the positions indicated by the arrows, then unscrew the screws at the same positions.
Step 2: Remove the Lower Half of the Case
With precaution, open the analyzer case and remove the lower half of the case, shown at the left side of the figure.
Unscrew the three screws at the positions pointed to by the arrows, and carefully separate the printed circuit board from the upper half of the case.
Step 3: The Power On/off Switch
A suitable switch is a miniature slide switch; typical contact ratings may be 6V DC, 0.3A. Take into account that the switch contact shall work with low voltage (few volts) and current (few tens of mA). However you should avoid micro-miniature switches, since they are too small to be easily handled and their current rating is too low (even only 1mA).
Step 4: Make a Slot for the Switch
Make a slot in the bottom half of the case, approximately in the position indicated in the figures. You may use drill tips or other drilling, cutting and grinding tools usually available as part of the accessory kit of a multifunction rotary tool like Dremel. In a similar way, remove the ribs on both sides of the slot, and try to create a smoother surface in order to let the switch body match the inner surface of the case.
The width and the height of the slot shall be high enough for the slide switch actuator to freely move between the two positions on and off.
Step 5: Stick the Switch to the Analyzer Case
Stick the switch to the analyzer case, on the inside, using a small quantity of strong fast-acting adhesive, e.g cyanoacrylate-based. Keep the switch body pressed against the inside face of the case for the time requested by the adhesive to work.
Be careful that the slide switch actuator can freely move between the two positions on and off
Step 6: Prepare the LCD Backlit Wires
Unplug the LCD backlit power cord, and cut the red wire approximately at half its length.
Remove 4mm of the insulating sheath from both sides of the cut of the red wire, and tinplate the copper with a soldering tool.
Step 7: Connect the LCD Backlit Wires to the Switch
Plug the LCD backlit power cord, then weld each red wire to a contact of the switch. Keep in mind that if the switch has three pins, it is of type SPDT (single pole double throw), therefore the red wires shall be welded to the central pin and to one side pin.
Step 8: Assemble the Analyzer Case
Now you can assemble the analyzer case, following the instructions on how to disassemble it.
The figure shows how the analyzer should look after the assembling phase; the arrow shows the position of the LCD backlit switch.
It is time now to test the analyzer "modding": connect the power cord and place a NiMH AA battery in a charger slot; act the switch and check if the LCD backlit turns on and off as required.
Now your MH-C9000 charger/analyzer has the LCD backlit on/off switch!
This is my first instructable, I hope it is clear enough for you.