Drew A Small Circuit In Tina By Examining PCB Solderside
My sister yesterday brought me an Alecto ATL-120 flashlight from her boyfriend that no longer was charging its 3 internal AAA batteries. The flashlight itself however worked fine with charged batteries inside when the top button was pushed that controls the intensity and the lower button that controls the on/off flash function. Normally when you put the flashlight in the wall charger, it will show that it is charging. But now it never did. So the best thing to do was to check the wall charger first.
But the first thing I tried was if I could measure any coil charger energy by inserting another coil into the charger coil that was attached to the bnc input of my oscilloscope. Nothing was measured.
The charger was really completely dead. It works just like most modern electronic toothbrushes do.
Opening the charger was easy by removing the 3 outer screws.
I checked the transistor marked A42 with my Peak Atlas DCA75 Pro. It measured fine being an NPN type transistor with an Hfe of 101. And all 1N4007 rectifier diodes were fine too. Also the HV reservoir capacitor worked fine. But it just didn’t oscillate, and so did not charge.
I drew a small circuit in Tina by examining above PCB solderside. The result is shown below.
The values of the capacitors and resistors are exact the values as used in this charger. Only the fuse and the charger coil are not known or identical to the circuit values. And C6 probably was a 10uF but because it was glued to the board I didn’t further check its value after I found the culprit. This circuit helps in understanding why the transistor no longer was oscillating.
The charger was dead because resistor R3 560K no longer was working and had to be replaced by a new 560K resistor. After that the charger worked like a new charger and I put everything back together.
Again another repair fixed at almost no costs. Only a new resistor was needed. Next photo shows the again charging flashlight. Shown by the blue light that normally doesn’t show.
Above the single culprit, the defect base circuit resistor of 560K. R3 in the Tina circuit.
The Alecto ATL-120 flashlight is a decent made product that even has silicon strips to keep the flashlight drip water proof. The silicon strips are used on the battery compartment and on top at the led cap. I only had to use some transparent glue to fix one strip back in place in the top.
Albert van Bemmelen, Weert, The Netherlands.
Please give a support by clicking on the social buttons below. Your feedback on the post is welcome. Please leave it in the comments.
P.S- If you enjoyed reading this, click here to subscribe to my blog (free subscription). That way, you’ll never miss a post. You can also forward this website link to your friends and colleagues-thanks!
Note: You can read his previous repair article in the below link:
(62)Dislikes
(0)
17 Comments
Leave a Reply
Mark
January 23, 2020 at 5:39 am
Well done Albert,
It's unusual to see just one resistor cause the fault. Good idea to make a schematic in front of you to make the diagnosis easier.
Albert van Bemmelen
January 24, 2020 at 2:00 am
Hi Mark. I beleave that it is true that often high value resistors get destroyed because they easily take all the high input voltage over them since the current through them is minimal. And that may be causing them to deteriorate more easily. For instance they use larger in length HV capable resistors in voltage probes. And they are not the normal R12 or R24 carbon types as was used here.
Albert van Bemmelen
January 24, 2020 at 2:25 am
Of course I meant to write believe instead of beleave sadly editing to correct it is not yet possible.
Mark
January 25, 2020 at 8:24 am
Good explanation - thanks 🙂
Francisco Rica
January 23, 2020 at 7:32 am
Goor repair Albert van Bemmelen. How you detect the problem in the resistor. I imaged that it was open. But your measured on board give you "OL" value in your multimeter?
Albert van Bemmelen
January 24, 2020 at 1:48 am
Indeed Francisco, it measured not being measurable. And the schematic confirmed that the generator without that base resistor never could work.
Beh
January 25, 2020 at 7:05 pm
This diagram is a good example of transformerless power supply .good job and thanks
Albert van Bemmelen
January 26, 2020 at 7:04 pm
You are right Beh. But these modern chargers of course are not completely transformerless because of the construction that in principle consists out of two separate coils forming a detachable transformer. And the second coil and the electronic charger controller circuit are placed in the interior of the flashlight around the battery compartment. As you know only the primary coil failed here to induce any energy to the second coil in the flashlight. Maybe in the near future our cars are charged this way with primary coils concealed in the road, and maybe we then at the same time are connected to the internet and to paying stations that control the energy to the charging unit of the car?
Parasuraman S
January 23, 2020 at 5:27 pm
Well done, Albert! Good to see a new device with all the details required! Many thanks for taking the pain of preparing a circuit diagram and sharing it here!
Albert van Bemmelen
January 24, 2020 at 2:20 am
It was an easy repair dear Parasuraman. It probably would have been a painful repair only if the flashlight had been defect too because it had a small pcb with a lot more small components on it. Including the electronic charger current regulator circuit.
Henrique J. G. Ulbrich
January 23, 2020 at 9:32 pm
Very good, Albert. Drawing a circuit by observing the PCB is a thing I use to do. It clarifies the ideas. Just for curiosity: did you measure the voltage across C6? (ultimately, it´s the circuit´s voltage supply)
Albert van Bemmelen
January 24, 2020 at 2:13 am
Yes, of course I did Henrique. The C6 voltage was at least ^2 times 230V = 325VDC so it was fine!
Robert Calk Jr.
January 24, 2020 at 3:01 pm
Good job, Albert! Another device saved from the garbage!
Albert van Bemmelen
January 24, 2020 at 5:57 pm
Indeed Robert. It was just one simple 560KB resistor to fix the problem for a big delicious Swiss milky chocolate bar! (LOL).
Idan
April 10, 2020 at 11:34 pm
I'm going to attempt this exact same repair. Checking the board with my Fluke now - might need to find a resistor as I'm certain I don't have one.
Henk-Jan
November 14, 2020 at 1:44 am
Dankjewel Albert, Thanks Albert,
Mine was broke to, didn't osscilate as well.
After i opened it up i thougth to myself: "I am not the only one in the world having this problem..." So, always when i think that i go to my best friend (Google) and i found your story.
In my case the transistor was broke (MPSA42), i had these in stock (?) because i bougth them to fix my Pinball machine 😉
Greetings from Zaltbommel, the Netherlands
Harrie
August 27, 2023 at 5:32 pm
I have the same problem with a flashlight battery that does not charge
Checking R3 560k shows that it is OK
Transistor unsoldered and with tester indicates it is an NPN with hfe of 85 so I think that is good
Only capacitor C4 of 562K deviates very strongly, I measure 0.11nf
Replacement has no effect
The circuit does oscillate
However, the generated positive voltage is too low
Ordered a new transistor anyway and replaced it
And yes it works again
I replaced the old C4 for the test
This resulted in a sine wave voltage of more than 550V rms
And the frequency had almost doubled
Also, almost the entire mains voltage (224V) was on C1
I think that's why T1 has deteriorated
Now I measure a sine wave across T1 of about 400V rms and a frequency of 28kHz
So thanks Albert for sharing, saves a lot of research
Greetings from the Netherlands
Harrie v Z