if i did a video, how would that make anyone think? it would just be more video, and no mental exercise is involved. i do not know that much about them, i just decided to figure it out in order to educate myself about electronics. that is why i spend so much time trying to get people to analyze their own equipment, to try to get people to learn how to think. but i know people prefer videos, because they don't have to think, to figure out what i am talking about by looking at their charger.
go dig out your dead charger, open it up and start looking inside at the various parts. there are smart people around who are EEs who post on here and they could explain it more intelligently, i just hack at it the same way i had to learn how to repair cars.
but i got to thinking it would help if i explained kinda in general terms what the power supply is doing. kinda like if people had a simple view of the overall way it worked it would make more sense.
but first, when looking at the charger, do the obvious things first. make sure the fuses are working, then see if there is 120V(or240 in europe and oz), are the leds lit but no output voltage?>>>maybe the fuse on the output is blown or the cord or plug has a broken wire or connector, is there a relay on the output that requires you to plug in the battery to turn on the output ?(i have seen chargers that were returned to the seller with complaints that there is no output because they measured it without connecting the battery, perfectly good charger, returned for refund).
these chargers, kingpan and EMC models are essentially identical, down to the resistor and capacitor values and the pcb layout is almost identical, but different enuff it does not violate trademarks i guess.
when you look inside you see there are two sections, one where the AC voltage come in and the other end where the DC current goes out. that big transformer is in the middle. so there is a "front end" before the transformer and "back end" where the current from the output of the transformer goes out to the battery.
the front end has the rectifier diode bridge which converts the AC to a stabilized high voltage DC signal that is floating on the that input capacitor, with ripples on top of it. that is the 320-340V you measure across the legs of the rectifier bridge. that 340V is then standing across the two totem pole npn (high voltage, high current) transistors. these two transistor are driven by an oscillator circuit that comes from that little transformer in the back end which itself is driven by the big 16 pin TL494 Integrated Circuit (IC) in the back end through the little transistors you see between the IC and the little transformer.
so the totem pole acts to push and pull current, at high voltage, through that big transformer. that current in the 'primary' windings of the transformer excites a current in the 'secondary' windings of the big transformer and that current goes out of the secondary into the back end of the charger.
the amount of current coming out of the transformer is dependent on how much current is pushed and pulled by the two totem pole transistors in the oscillator circuit of the front end. the TL494 can tell how much current it needs by feedback on it's input pins so it knows how much to push the little transformer to make it push the totem pole transistors in the front end to get the amount of current out of the transformer it needs to push up the voltage on the output.
so that is how it works, the push-pull circuit in the front end makes the transformer deliver current to the back end, and the TL494 maintains control over it. provides the feedback to keep it from blowing up as it would naturally without the feedback.
but there are two sets of windings in the secondary. one set delivers the current to the output through the big schottky diodes on the side there which convert it from AC back to a DC signal that is now floating on the output capacitor after some of the DC ripple is ironed out by that big toroid, called a choke, between the diodes and the capacitor/output.
the other set of windings in the back end are small and do not handle very much current at all like the main secondary windings do. this second set of windings is how the circuit current is generated in the back end to run the little electrical components and fan in the back end. this second set of windings delivers the current through that set of four little zener diodes sitting together in a row next to the transformer.
the four diodes make a rectifier diode bridge just like the one on the front end, just smaller and low voltage. you can see there is a little 35V capacitor sitting on the output from those diodes as it goes over to the input of the 12V regulator in a TO-220 package usually clamped to the case for heat sinking.
the output from the 12V regulator is used to supply current to the transistors, ICs and leds in the back end along with providing the current to drive the fan.
by now you will have seen all the components that do real work to make the current in the back end. the other stuff in the back end like the current sensing loop and the op amp that detects when the current has dropped to a low enuff level to switch the charger over to Constant Voltage (CV) at a point very close to the final voltage. that's what all that little stuff in the back end does, it doesn't make the current that goes to the battery.
so there are numerous and unknown permutations that can happen to prevent it from working to deliver current to the output, and limiting it to a few pictures in a video would limit what you have to consider has happened to cause it to fail. so this is where you have to use the only human function we have that separates us from bacteria, your mental faculties to analyze what information you can create by examination. this is why i find thinking enjoyable and some do not and prefer videos.
in most cases the failure will be obvious, a bulging capacitor, a black smoky spray under a transistor or loose wires even should draw you attention. but it can be systematically analyzed by starting with the fundamentals of the circuit and testing with the voltmeter to see if there is voltage present at various points in the circuit either in the front end or back end.
in the case of corbin's charger i noted there were no leds lit in the back end so the first thing i tested with the voltmeter was the voltage on the output of the 4 little zener diodes which supply the circuit current to the back end. usually about 20V DC on the end of the zener diode, but there was no voltage, so i knew that the transformer was not being excited by the oscillator driving current in the front end, (or the transformer could be shorted, or the windings open for that set of secondary windings).
so i looked into the front end, measured the voltage where the AC comes onto the board (use the high voltage AC on the meter), it was ok, then i checked the high voltage from one end of the rectifier bridge to the other end (1000V DC scale) and measured the 327V DC, ok.
so i knew now that there was voltage present on the totem pole transistors and the next thing to do was to measure the voltage of the transistors that are driven from that 327V. i expected the voltage to be evenly split between them. and i knew that the collector of the lower transistor (the high side of the bottom transistor) is connected to the emitter of the upper totem pole transistor (low side of the upper) so if i could measure the voltage at that spot in the middle i figure i would learn something.
but you cannot reach the legs of the totem pole transistors because they are so far down and underneath that clamp which is ground so if you short the transistor legs to the clamp with your voltmeter probe it will blow up the transistor and make a mess of your probe. so that is why i used the fact that the collector of the transistor is connected to the tab on each transistor.
so i put the voltmeter probe on the tab of the lower transistor (because that is the middle where the emitter of the high side and the collector of the low side split the voltage) and measured the 160V DC (using the 1000V DC scale on the meter). then i measured the voltage of the tab on the high side transistor and it was only about 190V and not the 327V which i expected from the voltage on the rectifier, so that was the clear indication that the transistor was shorted and the current was flowing though the transistor when it should be turned off and the voltage drop across the shorted transistor added a little voltage above the tab of the lower transistor.
so that was enuff for me to take it apart and remove the transistor and replace it with another one to repair it. but to be certain, after i took it apart, i measured the pn diode junction of base to emitter of both transistors and the lower one showed the 450mV of a normal pn junction and the high side transistor showed 112mV of a shorted junction. also by putting the red probe on the collector(middle leg) and the black probe on the emitter(left leg) the diode tester could not push current through the good transistor so it read open circuit but when i put the diode tester across the collector-emitter of the high side transistor it measured the same 112mV of the short. so it was confirmed that the high side transistor was bad, cut the legs off, unsoldered the little bit of leg left and soldered in the new one leaving the space on the legs so i could bend it to the little dog leg to make it fit flat against the side of the case when it was clamped later.
it could have been different and the low side transistor could have failed and in that case i would have expected the tab of that low side transistor (the collector connected to the emitter in the middle of the totem pole) to be very low, say around 20-30V like the other one i just discussed, and if it was low then you would be able to assume the low side switching transistor had failed and need to be replaced.
but measure both to be sure you know whether only one or both of them failed before you take it apart. test them both with the diode tester when you get it apart.
there are other ways the chargers fail too. often the schottky diodes will just become exhausted from running so hot for so long they finally go out. in that case you would have the leds lit in the output because the front end is acting normal but there is no current going through the diodes. to test for that you use the DC scale and put the black probe on ground in the output, the - spot or you can put the probe on the wire loop used for the current sensor since it is easy to access and is also at ground.
then you measure the voltage on the big wide trace coming off the schottky diodes. if there is no voltage then you need to test the schottky diodes with the diode tester.
if there is voltage coming off the schottky diodes then the next thing to test is the big toroid since sometimes it will get so hot it melts the solder out of the connection or can even burn the trace off, but that stuff is usually obvious.
the biggest problem for these chargers in the back end is where the choke is so hot that it melts the varnish on the pcb that insulates the trace coming from the 4 zener diodes for the circuit current and running over to the 12V regulator on the side.
that trace runs directly underneath the choke and i have seen several instances where the high voltage of the output going through the choke is shorted to the lower 20V on that trace running to the 12V regulator and that high voltage is very very hard on the electrical components in the back end.
you will see the blown up (by high voltage of the output) small capacitors and sometimes other parts but when that happens it usually stops working immediately but sometimes the short can be really bad, and difficult to repair because the little caps are hard to unsolder and replace.
the other problems i have seen involve the charger basically running full out with high high voltage appearing on the output, like 112V or so and that will blow up the output caps. this is caused by failure of the feedback mechanism the TL494 should provide and is something i have had trouble identifying. i have even replaced all the electrical components in the back end of a charger like this and it still was not functional and finally blew up the output caps so much i gave up.
i had the top off one time and the output caps went off like a roman candle, shooting pretty sparks and smoke up into the sky. another time it happened inside the charger with the cover on and made a huge black smoke cloud inside above the output cap.
good luck, go look at it and start figuring out what you are looking at, then think of how to test it for what could be wrong. maybe i can help, maybe not. make a video if you wanna to show how far you got and why you did it for us to comment on.
if you wanna see a schematic of the charger circuit you can look at this work by albert vandalen, thanks again so much to albert:
http://www.avdweb.nl/solar-bike/electronics/portable-lightweight-lifepo4-ebike-battery-charger-800g.html