Another Adapter Repaired 4.2V 0.5A And Tested Using Supertip
This small adapter repair was put aside for quite some time after I already had repaired all obvious defects and had also fixed a burned through copper track. And because the 4.2V 0.5A adapter board still refused to start working after all the destroyed parts were replaced I once and a while picked it up to examine the small adapter board again. And why this adapter short circuited and blew away a primary copper track in the process was unknown.
Until I recently on one of those days finally found why it still wouldn’t work! Of course I also had drawn a schematic by examining the board layout. Here it is, followed by the fixed solder board side:
It had no active PWM controller, only 2 primary transistors. One 8050 and one 13001 transistor , plus the standard optocoupler a 4 pins PC817C. Plus 3 resistors and a primary 400V 2.2uF e-cap and a single 10nF primary capacitor. Below the component side also after the defects were fixed.
Sad thing is probably that I do not know what this HD-33A adapter was made for because of the secondary connected DUO-LED, I guess it was for some kind of charger. But I am afraid that I already have used the original housing it came in for other purposes. So of that black plastic 230V AC case I now only have a few photos left. Below photos show the original 230V AC housing.
It turned out that not only the primary components on next photo needed replacements but also the secondary 3.0V zener and the 220uF were defect!
On above photo my little but great working universal digital tester that disapproved the PC817C optocoupler. You can just see the scrolling ‘r’ of the “error” report. This tester also tests Opamps, TTL/CMOS ICs and even a few other analogue amplifier ICs. And operates on a single AAA cell! This little portable affordable tester never disappoints, and it is incredible how they could design it so tiny with all its functionality!
I afterwards also found 2 left cold solder joints that only showed up when I juggled with the legs of the Duo-Led connected to the bigger 2.2 Ohm (1 or 2 Watt) resistor on the + output track, and the cracked track to the single 230V AC input rectifier diode.
All that time it was just the secondary 220uF 10V e-cap in above photo that still was the culprit because before it was replaced there was no output on the secondary side and only the DUO-LED lit op in green. The secondary 220uF e-cap only had a low pF value left which was totally unexpected.
After I had also replaced this little 220uF bugger the adapter finally came to life and my repair successfully ended here!
Because I previously had no 3.0V zener I soldered in a 3.5V zener, why the adapter output voltage was with an output voltage of 5.2V obviously a little higher.
And my previous ‘repair’ about the super safe method on testing these small power adapters without the commonly used light bulb and unsafe live AC power line connection, came in very handy again!
After I asked my electronics friend Erik about this charger I now know what this adapter was used for. I have to replace the zener by an exact 3.0V value again because the adapter was used for charging a 18650 3.7-4.2V Creon 3W Led torch/light. It apparently got blown immediately after the Led light was switched on while it was charging. When assumably the current became too high for the charger to deliver both the charging current and the Led light current. And why my friend bought 3 extra adapter chargers to make sure his Led light always can be charged.
Below follows a photo of the working safely powered power adapter under test.
Using the DY294 also just worked but it couldn’t provide the necessary higher supply current for the adapter under test fast enough to activate the adapter long enough to be able to make a photo. Because the adapter used so much energy from the charged primary 2.2uF HV e-cap it already had discharged the moment the adapter started working.
If this adapter had a real PWM controller chip that controlled the step-down conversion from AC to DC it should have worked also good enough with my DY294. But the Omnipotence Backlight tester was again able to deliver enough current (probably at least 150mA!) which also worked on this less economic more energy consuming power adapter.
The red wires provide the DC voltage input into the AC adapter. The green and white wires are the + and ground adapter output to my DMM voltmeter.
(AC anode diode to +, other AC input -). Otherwise it won’t work because of the single rectifier diode. (not an AC diode bridge rectifier).
I’m so glad never ever again having to connect these little power adapters straight onto the dangerous live 230 VAC power lines just to test these small charger adapters!
Albert van Bemmelen, Weert, The Netherlands
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Note: You can read his previous repair article in the below link: