I recently repaired a Kenwood TM-731A 2m/70cm mobile radio. It appeared that the backup battery was dead since it would no longer retain any memories after power was removed.
Checking the battery, it was indeed dead. I replaced that but noticed the board was coated with what could have been electrolyte leaking from the dead CR2032 battery. I removed as much of the leaked liquid as I could from the circuit board using flux remover.
To replace the four bulbs used to illuminate the LED display, I had to remove the front panel. That can be tricky on these old Kenwood radios since the foam that secures the buttons in place turns to sticky goo after so many years of use.
Like most radios I’ve come across, the backlight consists of multiple, in this case 2, pairs of 6 volt bulbs in series with a resistor.
After carefully bending the metal ears straight and releasing the LED display away from the control board, I desoldered each bulb and replaced it with a super bright white LED, keeping track of the polarity of the LEDs. I replaced the 10 ohm series resistors with 680 ohm SMD resistors for the new 20mA LEDs
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