Please help repair a Makita jobsite radio BMR 102

[max.wwwang]

The Aux in 1/DC in board


Front/JW301: Left 4 wires are from the Aux in 1 jack, the right 2 are for main DC power in (white +/blue GND).

CN301 comes from the battery board carrying - two wires for the main battery. Inserting the DC plug will break the power from the main battery (from CN301).

(This is a common problem of this model but this unit does not have this issue.)

[max.wwwang]

The batteries board and a tiny switch board (for sensing a main battery in position).


# wires on the top go to the position switch (the second photo). When there is no main battery (one type of the many that are acceptable) the right two points are connected, otherwise the left one and the middle.

Top-left corner, the top 3 wires go to the LCD board - the top and bottom ones are wired to the backup batteries (3V) by the traces.

The socket below goes to the backup batteries compartment (3V, 2x AA).

[max.wwwang]

The audio power amp chip is LA4631. Datasheet here: https://pdf1.alldatasheet.com/datasheet-pdf/view/439056/SANYO/LA4631.html

One thing is that the physical specs of the chip in the radio/amp board is different from this datasheet. Also mine has only 12 pins, the datasheet has 13 (though #13 is N.C). Otherwise the wiring is similar: pins 8/12 go to the speakers. So pin 7 should be Vcc. I got only 5V here (with or without DC in). The datasheet requires 14V.

[timenutgoblin]

I think that the reason the op-amps are measuring 0V on the power supply pins is because they are powered by the 5V voltage regulator which is 'disabled'. Perhaps you could confirm this with your DMM. V+ is pin 8 and V- is pin 4.

On the Radio/Amp board there are two transistors Q8 and Q9. I think this is a DC/clipping detection circuit for the audio amplifier IC. The circuit connects to the LCD board via the grey flex cable.

On the LCD board, there are zener diodes that may have something to do with battery voltage detection; ZD201, ZD202 and ZD203.

Could you check IC203? It's located under the shield. It looks damaged in the photo.

[max.wwwang]

I think that the reason the op-amps are measuring 0V on the power supply pins is because they are powered by the 5V voltage regulator which is 'disabled'. Perhaps you could confirm this with your DMM. V+ is pin 8 and V- is pin 4.

Both rails of both op-amp chips measure 0V. This obviously does not seem good.

On the Radio/Amp board there are two transistors Q8 and Q9. I think this is a DC/clipping detection circuit for the audio amplifier IC. The circuit connects to the LCD board via the grey flex cable.

Yes, both transistors are connected to the speaker outputs and audio amp IC.

On the LCD board, there are zener diodes that may have something to do with battery voltage detection; ZD201, ZD202 and ZD203.

These diodes look good with the diode test function of my MM (though only tested inline without taking any of them off - no short circuit detected through these diodes).

Could you check IC203? It's located under the shield. It looks damaged in the photo.

Good spotting! There is indeed some dirt on it but after cleaning, it does not appear to be physically cooked. But I'm unable to read its label.

[max.wwwang]

Is this transistor (B1143) the culprit (highlighted in the photo)?

From the top downwards, the pins are E/C/B with C going to the audio amp IC (pin 7, expecting 14V). They measure 16.7V/1.2V/16.5V, respectively.

(I remember once I got 5V on pin 7 of the amp IC. Don't know why I got only 1.2V now.)

Is there a bad smell here? (Is the V drop between B/E, 0.2V, OK?)

[max.wwwang]

Found a unit with the same problem on sale on eBay

[max.wwwang]

Asked makita service with this:

I have a Makita Jobsite Radio BMR102 that does not work. I plugged the AC adapter without using a main battery (I've put in two new AA batteries as backup battery according to the user manual). It does not turn on when pressing the power-on button. The LCD gives an "E" with a flashing low battery sign.
 
I checked the user manual. It only says when the backup battery is low, it will show a low battery sign with a flashing "E", which is different from what I got. The manual does not include information about a flashing low battery sign and an "E" (that does not flash).
 
Would really appreciate if you can let me know what this means and how I can possibly fix this.
 
Thank you very much for your help.

I got this:

That’s likely a fault with one of the main boards, if you send it down to us we can assess and fix it for you. If you could also provide a copy of your proof of purchase that would be good.

[Muttley Snickers]

Found a unit with the same problem on sale on eBay

The local council recycle center/ tip shop had an entire wall stacked with these job site radios about a month ago. They would all be warranty returns and likely deemed beyond economical repair, possibly due to an inherent fault or bad batch. I haven't been back there since but might go for a look this week, it's amazing the stuff that gets chucked out.

[max.wwwang]

Please have a look. Haha

[max.wwwang]

New development --

After a careful close examination and some fiddle-around measuring the connectivities and voltages, it cameto be that a fine trace under the belly of a transistor seemed broken - measuring different voltages at its two sides. After connecting it with a jump wire, as shown, now the low battery sign is gone, and when pressing the power on button, the LCD backlight lit up!

Also, the +ve rails of the two op-amp chips all give 5V (presumably this is a good one?), #7 pin of the audio amp chip gives 14V (correct), the Vdis/Vadj pin of the voltage regulator give 2V (enable) and in turn, its Vout gives 5V (also correct)!

All good. However, the front panel does not respond further and there is no radio or noise coming out of the speakers. And it can not even be turned off by pressing the power button.

Also, the voltage regulator chip is very hot (it does not have a heatsink with it).

Is this closer?

[timenutgoblin]

Are you able to tune the radio frequency with the rotary encoder (ROT200)? Try pressing in the rotary encoder to select between volume and tuning. Maybe the volume is muted?

[max.wwwang]

I tried turning it, pressing and long pressing. But no responses whatsoever.