Please help repair a Makita jobsite radio BMR 102

[max.wwwang]

Symptom: Does not turn on with DC from the original adaptor. The LCD display works, as well as setup of clock and alarm etc. with backup batteries installed but won't turn on when pressing the power on button, it gives "E" with the low battery indicator flashing.

I've exhausted all I could find online, webpage or youtube videos but have not found or figured out a solution.

Problems often happens with the DC input jack but it's ok.

Apart from the small boards for DC input/audio output and for battery pack input, there are two main boards. I would assume one is for the radio another is for the microcontroller/user interface. There is a flat cable connecting both, I would assume it's largely one way - from the LCD board to the radio board except perhaps a signal (or power) input from the radio board, to which the DC input jack board is connected, at least for the LCD board to know whether there is power. This is based on the fact that, without connecting the DC adaptor or installing the main battery, connecting the cable from the backup battery to the LCD board will cause the LCD display's to reset (briefly showing all the segments). And with only the backup battery, I can set up the clock and the alarm.

Its user manual can be found here: https://media.makita.co.nz/_media/user-manuals/B/BMR102-UG.pdf

I couldn't find a service manual or its schematics online.

Thanks for any help.

[sean0118]

Check the power rail voltages at the ICs

[max.wwwang]

Thanks for the hint.

There are two dual op-amp chips 4580. What are the design Vcc and Vee? Can they be as wide a range as +/-2 ~ +/-18V (based on the feature "operating voltage (+/-2 ~ +/-18V)")? I only got very close to 0 on both of the Vcc and Vss pins of both chips. This does not seem right.

There is a voltage regulator SA78RL05F. But I only found the datasheet for SA78R05F (without an "F" in the middle). According to this datasheet, its input power rating is 7V (but the absolute maximum rating is 35V). My input is approx. 17V (wait - why is it 17V when it's said on the case to be 12V output?). Almost 0V on the second pin (output), which is supposed to be 5V according to the datasheet of SA78R05F (assuming they are largely the same?). would this voltage regulators probably be the culprit?

Tried to feed a 5V DC directly between its output pin (#2) and GND but there was no miracle happening.

[Audiorepair]

Such op-amps would normally have something like +12v/-12v supplies, or 15v is also pretty common.

Sometimes they will only have one positive supply though, so you may see something like 15v or higher on the +ve rail and the -ve rail is at 0v.
In this case the input and output pins will be at half the +ve rail voltage.

If it does use a dual supply and the negative is missing, so it looks like +15v on the +ve rail and zero on the negative, the op amp outputs will be slammed at either full supply voltage or zero, not at half the supply voltage as in the single rail case.

[max.wwwang]

Such op-amps would normally have something like +12v/-12v supplies, or 15v is also pretty common.

Sometimes they will only have one positive supply though, so you may see something like 15v or higher on the +ve rail and the -ve rail is at 0v.
In this case the input and output pins will be at half the +ve rail voltage.

If it does use a dual supply and the negative is missing, so it looks like +15v on the +ve rail and zero on the negative, the op-amp outputs will be slammed at either full supply voltage or zero, not at half the supply voltage as in the single rail case.

That makes sense. No need to have a 12V adaptor if the circuit does not need a voltage higher than 5V. It's likely the positive rails of the op-amps are supposed to be +12V?

One strange thing is the AC adapter gives 17V DC but its label says 12V. Surely this is not right?

[Audiorepair]

Ah, I replied without looking at the photos.
I assumed, like most contemporary equipment, there would be some internal power supply generation from DC converter chips and the like.

Yours looks pretty simple, so most probably there is a single supply rail to the op-amps, which will probably not be 5v, but somewhere between 5v and 12v.


A 12v linear transformer may very well put out 17v if it is not loaded, in circuit and supplying power this will drop to more like its nominal 12v.

[max.wwwang]

A 12v linear transformer may very well put out 17v if it is not loaded, in circuit and supplying power this will drop to more like its nominal 12v.

Thanks. So I don't need to look into the AC adaptor (which is difficult to open ).

[Audiorepair]

Is it a Switch Mode Power Supply or a transformer in a plastic box?

[timenutgoblin]

Symptom: Does not turn on with DC from the original adaptor. The LCD display works, as well as setup of clock and alarm etc. with backup batteries installed but won't turn on when pressing the power on button, it gives "E" with the low battery indicator flashing.

Is the backup battery on the PCB or in a separate holder?

Check diode D301 and connector JW301 both located on the small PCB. Check for connectivity/conductivity between JW301 (small PCB) and CN1 (large PCB).

[max.wwwang]

Is it a Switch Mode Power Supply or a transformer in a plastic box?

The latter.

[max.wwwang]

Is the backup battery on the PCB or in a separate holder?

The latter, with the 2 wires going to a small board coordinating all the inputs from the main batteries (not used by me) which has a cable of 3 wires going to the LCD board. Reconnecting this cable (with backup batteries in) will cause the LCD reset - that's why I believe the LCD/control board is ok.

Check diode D301 and connector JW301 both located on the small PCB. Check for connectivity/conductivity between JW301 (small PCB) and CN1 (large PCB).

This is very detailed and specific, and sounds promising! Thank you. Will check it out later today.

It also came to me that I need to check the capacitor connected to the output pin of the voltage regulator, its 0V output can be caused by its failure?

[max.wwwang]

Check diode D301 and connector JW301 both located on the small PCB. Check for connectivity/conductivity between JW301 (small PCB) and CN1 (large PCB).

All checked. No problems. But thank you. Obviously, you know this model very well. Did you repair one of this before, or at least you looked closely into it? Are you aware of its schematics anywhere?

[timenutgoblin]

According to the User Manual it mentions that the main battery and backup battery may need to be replaced. Check page 5 of the User Manual (I have attached a screenshot). It also mentions that the power adapter does not charge the battery. Also check page 4 regarding battery installation.

Unfortunately, I don't know about any schematics or service manuals.

[max.wwwang]

According to the User Manual it mentions that the main battery and backup battery may need to be replaced. Check page 5 of the User Manual (I have attached a screenshot). It also mentions that the power adapter does not charge the battery. Also check page 4 regarding battery installation.

Unfortunately, I don't know about any schematics or service manuals.

Thank you. I’m aware of this. I also noticed that there is a difference from the signal for low backup battery and what I got. For the former, as described in the manual, it’s a flashing “E” letter and a low battery sign (that probably does not flash, but this is not specified in the manual). In my case, it’s an “E” letter that does not flash but with a flashing low battery sign.

Strictly speaking, these two are different. But there is no description of what exactly this means, which is a bit strange. I'm using two new AA batteries (according to the manual).

[timenutgoblin]

There is a voltage regulator SA78RL05F. But I only found the datasheet for SA78R05F (without an "F" in the middle). According to this datasheet, its input power rating is 7V (but the absolute maximum rating is 35V). My input is approx. 17V (wait - why is it 17V when it's said on the case to be 12V output?). Almost 0V on the second pin (output), which is supposed to be 5V according to the datasheet of SA78R05F (assuming they are largely the same?). would this voltage regulators probably be the culprit?

Tried to feed a 5V DC directly between its output pin (#2) and GND but there was a miracle happening.

Did you get the radio working? Maybe the voltage regulator is faulty or is not switching on. How many pins does the voltage regulator have; 3 or 4?

[max.wwwang]

Did you get the radio working? Maybe the voltage regulator is faulty or is not switching on. How many pins does the voltage regulator have; 3 or 4?

Sorry, I missed a "no".  Not working.

Yes, I think the voltage regulator is possibly the culprit. It is a SA78RL05F but I can only find the datasheet for SA78R05F (without an "L" in the middle). It has 4 pins: Vin, Vout, GND, and Vdis/Vadj, according to the datasheet of SA78R05F. Trying to replace it, but I couldn't find either SA78RL05F or SA78R05F on sale online.

[timenutgoblin]

I noticed that there is another small PCB in the bottom right hand corner of your second photo with black/red twisted wires and grey coloured wires connected to it. I think this is the same PCB shown in a YouTube video. I have attached a screenshot from the video.

Here is the link: https://youtu.be/Vt0xrWyUyJ8

[max.wwwang]

I noticed that there is another small PCB in the bottom right hand corner of your second photo with black/red twisted wires and grey coloured wires connected to it. I think this is the same PCB shown in a YouTube video. I have attached a screenshot from the video.

Here is the link: https://youtu.be/Vt0xrWyUyJ8

Yes, that’s the board for the various kinds of main batteries. I watched this video though didn’t quite get what the fix was. Since I’m not using main batteries (I’m using the mains adapter only), I think this is not relevant to my case. No matter whether or not I connected this main batteries board to the (another small) DC input board, I got the input power voltage of 17v on the radio board.

A new thought is - it appears to me that the voltage regulator is possibly used in the disable mode (as opposed to the adjustable mode, according to the data sheet). Because all the 3 pins other than Vin gives 0V, it’s possible that even if the chips is not broken it’s disabled (making Vout 0V, as opposed to 5V). There must be a way on this radio board to send the status of the main DC power to the LCD board through  grey flat cable (which is the only one between these two boards) to it for it to be able to determine whether or not to show a low battery sign. If for whatever reason it sees a main battery fault (then shows a low battery sign), it will probably not send an ‘enable’ (I.e. high, which is 2V according to the data sheet) to the Vadj/Vdis (4th) pin of the regulator.

So there is probably a problem here.

[timenutgoblin]

There is a component labelled ROT200 on the LCD board which might be a rotary encoder for the volume control and radio tuning. I'm wondering if it might be faulty and preventing the radio/amplifier from working properly. At first, I thought it was a potentiometer.

Have you checked if the speakers are working? Do you hear any hissing or clicking when connecting or disconnecting power? Is the audio amplifier IC getting any supply voltage? You mentioned in an earlier post that the op-amps are measuring 0V. Maybe check them for short circuit?

[max.wwwang]

There is a component labelled ROT200 on the LCD board which might be a rotary encoder for the volume control and radio tuning. I'm wondering if it might be faulty and preventing the radio/amplifier from working properly. At first, I thought it was a potentiometer.

Yes, it's a rotary encoder not a potentiometer. It's working without a problem. After pressing the setting button I can use it to adjust the clock and alarm (So I think the micro controller module is working fine).

Have you checked if the speakers are working? Do you hear any hissing or clicking when connecting or disconnecting power? Is the audio amplifier IC getting any supply voltage? You mentioned in an earlier post that the op-amps are measuring 0V. Maybe check them for short circuit?

Yes, speakers are good. When reconnecting the backup battery (with or without the AC adapter connected), I can hear a short beep from the speakers, along with a brief display of all the segments on the LCD (sort of self-test I think).

Along my thought of input +17V going from the radio/amp board to the LCD board, yes, there is a line feeding this voltage and this for sure has come to the LCD board. No further findings suspicious along this line. Maybe I should look along another line - why the positive rails of the op-amps give 0V.

[amyk]

Could you post good aligned photos of both sides of the baords? That looks vintage with the through-hole components and single-sided boards. It won't be hard to create a schematic.

[max.wwwang]

[ Specified attachment is not available ]

Could you post good aligned photos of both sides of the baords? That looks vintage with the through-hole components and single-sided boards. It won't be hard to create a schematic.

Sure.

Radio/amp board front

Two pairs of wires (bottom right) go to speakers.

CN4 (not clear, the one below JP 28) goes to Aux in 2. CN1 goes to the Aux in 1/DC in board. CN2 goes to the LCD board.

[max.wwwang]

Radio/Amp board back

[max.wwwang]

LCD board front

[max.wwwang]

LCD board back

The bottom right corner is the socket for the 3 wires coming from the batteries board. The left one and right one are for the backup battery input. The middle one I suspect is for detecting the main battery position switch. With DC plugged in, it gives 5V (1.9V when without DC in). it's pulled to 0V when manually pressing the micro switch (pretending there is a battery).