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.
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Note: You can read his previous repair article in the below link: