Makita DMR115 repair - no power

A colleague of mine asked me to take a look at his Makita work site radio. Completely dead. Not a single sign of life, not with any type of battery, and not with DC power input.

Makita has put the screws in the battery compartment in a very deep hole. And it requires a security Torx TX15 (Wera has a good one Model 05138269001 with a 300mm shaft). Once that is removed, you have to use a big hex bit to remove the screws that bolt the aluminium handles to the chassis. All that is left then, is to remove the bottom woofer grille, with 4 Philips screws. 2 screws are again hidden behind this mesh. Undo those, and we’re in.

The first thing I noticed was a bloated cap - C13. A 1000uF/25V “GD”-brand capacitor. An unknown brand to me, which I replaced with a (physically) larger 1000uF/63V Nichicon cap. Given that it’s quite close to the heatsink, it should fare better.

As said - the replacement cap should last a bit longer…

That wasn’t the only problem. Power was also not being fed into the board. That came down to the 5A fuse that blew next to connector CN4. I replaced it with a piece of calibrated wire.. Just kidding. I didn’t have any SMD 5A fuses, but took some hookup wire which I use to repair PCB traces. It blows around 4.8 A, good enough.

Ok, power is being fed into the board, the radio turns on. But.. It also doesn’t turn off anymore when you use the power button. That comes down to these 2 circled MosFET’s. They are AO3403 MosFET’s (by “Alpha & Omega Semiconductor”). I replaced them with some equivalents I had around. They are used as a simple DC switch. Nothing critical. P-Channel MosFET’s. Drain-Source voltage -30V. Gate-Source voltage +-12V. 2.6 A current rating. RdsOn < 115mOhm. Just look through your parts bin. You’ll find something that fits. I circled the location in the picture below in case others face the same issue that they cannot turn the radio off anymore, after fixing said fuse and capacitor.

Happy fixing! - 73 de ON8AD