The Radiolink CP620 is a hybrid charger, a very good charger that greatly increase the life cycle of Lipo batteries. I have some Lipo batteries which are used for close to 200 cycles and yet they are still doing well in flights.
The setback of CP620 is that it has no protection for wrong battery connection. If you connect the balance connectors wrongly (reversed direction) or connect two cascaded lipo batteries to the charger, the charger will be damaged. I personally have made wrong connection in three occasions. LOL, I thought I was careful person.
Fortunately the damages to the charger when making such wrong connection is easy to repair.
The damages are usually limited to PCB traces broke (burnt) or MOSFET faulty (short) near to the balance connectors area on the PCB.
Here are the steps to repair the CP620 charger.
To open the top cover you need to remove the Aluminium sheet on the top cover. First, remove the four screws at the front. You then need to plie and remove the Aluminium sheet from the front. Note that the aluminium sheet is hold to the top cover with double-sided tapes in the area of the four buttons. Once the aluminium sheet is removed you need to remove the four screws at the four corners of the top cover.
You will see a control board that is mounted on the inside of the top cover, and a power board on the base plastic. Carefully remove the cables (one power cable , one flex cable  and two fan cables [1&2]) that connect to the control board. Pay attention to the flex cable, remove it from the power board's end. Use your finger nail or a tweezer to flip the black plastic piece upward and you can then easily remove the flex cable.
The power board is mounted to a big heatsink. Remove the 8 screws on the power board.
PCB traces are likely to be broken.
These are the 14 MOSFET that likely to be faulty. These MOSFETs are all PH5030AL (N-Channel), SOT-669 package.
The PCB traces around the MOSFETS can also be broken due to wrong battery connection.
An example of a broken (burnt) PCB trace:
Repair the broken PCB traces with wires. The wire must be able to carry at least 5A of current.
To determine which MOSFET are damaged you need a digital multimeter, and select the "Diode" mode.
Pin Assignment of MOSFET (PH5030AL):
Identification of bad MOSFETs:
- Put the black probe on the Source pin, and the red probe on the Drain pin, there should be no reading on the multimeter, if there is any reading it mean the MOSFET is bad.
- Put the red probe on the Source pin, and the black probe on the Drain pin, there should a reading on the multimeter (around 0.450V to around 0.480V), if the reading is close to 0.000V it means the MOSFET is bad.
Remove and replace all the damaged MOSFETs with a hot air gun (for SMT soldering).
Be careful not to blow away the chip componets near to the MOSFETs.
It is not difficult to remove and replace the MOSFETs even for a first timers.
Search and watch the youtube video instructions on how to remove and solder SMD components.
Do a quick check if the charger is okay.
Connect the power cable and flex cable between the power board and the control board, without the connecting fans and mounting screws of the heatsink.
Turn on the DC input supply to the charger. Connect a battery (only the balance connector will do) to the charger to see if the charger is okay. Make sure all the cells' voltage can be read by the charger.
Place and tighten the 8 screws that hold the heatsink.
Take care of those thermal tapes, make sure they are properly placed and aligned before you mount the power board to teh heatsink.
Connect the fan connectors. Complete the assembly of the rest of parts.
Hope this is helpful for those who want to repair the charger themselves.