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 adapterboard
still refused to start working after all the destroyed parts were replaced I once and a while picked it
up to examine the small adapterboard again. And why this adapter short circuited and blew away a
primary copper track in the process was unkown.
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
secundary 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 secundary 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 secundary 220uF 10V e-cap in above photo that still was the culprit
because before it was replaced there was no output on the secundary side and only the DUO-LED lit
op in green. The secundary 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 supersafe 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 electronic 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 diodebridge 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.