If the charger is working properly, thermal imaging won’t tell us much here, as I’ve never come across a case where something heated up immediately; however, there are three components that overheat particularly badly despite the unit functioning correctly: the diode on the secondary side (D104), the MIP itself gets quite hot, and I think there are three resistors on the primary side that discharge the charge – that’s how I recall it, though I can’t double-check right now; but the temperatures of these components didn’t exceed 40 degrees; the rest were at room temperature.
In my opinion, you can’t test the optocoupler properly with a multimeter until you’ve fitted it; if you apply the correct voltage to the diode, it should work; but if you fit a faulty one, you’re out of luck; I’ve never been able to measure it correctly. Apart from that, out of a hundred power supplies I’ve repaired, let’s say I’ve had about three cases where the optocouplers were damaged, but that was because the electronics were completely blown, for example after a storm.
So, as far as I’m concerned, if the processor isn’t working properly, you won’t have a green LED.
Behind T2, you’ll find capacitor C111 – check that it reads 8.4V and that there’s no short circuit;
Next, look for C141 – it must read exactly 5V. It’s on the left in the schematic I’m showing, which depicts the circuit with LED100
Check the voltage at pin 29 of the processor, as this pin controls the LED; there must be 0V there (during standby and whilst the battery is charging; if 5V appears there, the LED will go out and one of the protection circuits – e.g. thermal, current or voltage – will have tripped).
Pin 29 should tell you whether a protection circuit has tripped or if there’s a short circuit somewhere.
Above all, start by checking whether the microcontroller has a stable 5V supply on pins 14, 21 or 25.
And if your processor is blown, the charger is ‘rubbish’ because you won’t be able to reprogram the processor as you won’t get a signal; the chip itself is fairly easy to source. Unless, of course, you’ve got a spare and can take one from another charger that has a burnt-out primary circuit. Because damage to the secondary circuit in these chargers is rare, unless there’s mechanical damage to the laminate or water damage.
For the green LED to work, there doesn’t need to be a battery, the IC1 chip or transistors; it’s important that the secondary side is working properly, because the voltage from T2 powers the processor, and it sends a signal via PC5 to activate the 13V circuit; only after the battery is inserted does the processor activate PC4, supplying power to IC1, which in turn activates the main converter and regulates it via PC3. It is also important to note that, once the battery is connected, there is a quick check to determine what voltage the charger should be set to, along with a current measurement; and this is precisely where chargers in this sector fail – they start charging and then, after say 30 seconds, switch off because the converter is not supplying current. If the charging cycle switches off immediately after the relay is activated, this means a safety mechanism has tripped – for example, a faulty PTC1 = 470R or TC101 = 10kR, which, in my opinion, is used in this charger as a fan safety device; if the fan were to stop spinning, this sensor would detect it and switch off the converters.
