[quote]Thanks for the reply[/quote]
[b]You're welcome
My apologies for the late reply. Of late I've been having major lower back issues and sitting down in front of my PC would have made it worse.
I have to admit, I'm not familiar at all with this BMS, so if I sound a bit ignorant, you'll know why.
Provided you have a reasonably fine tip on your soldering iron, you should be able to replace the suspect Mosfet without too much difficulty.
A word of warning at this point. Due to the small size of the transistor and the pads its joined to, excessive heat from a soldering iron can matter considerably compared to through-hole components which are usually more bulkier and more heat tolerant. You MUST be conservative in the heat department. Its easier said than done, but you have to try and make a conscious effort, otherwise you risk lifting up pads and damaging the new transistor.
There are a few choices on how to remove the transistor, each has its own dangers, so I'll try suggesting the better options and leave the final choice up to you.
(1) If you have a fine pair of side cutters, you can actually nip each leg where it enters the Mosfet's substrate. But this has to be done extremely carefully, as to prevent you accidentally ripping up the appropriate pad the leg is joined to as you squeeze the cutter handles together. (If you want to go down this track, let me know, and I'll do my best in explaining on how to do it. The next option is more tedious, though a more safer alternative).
(2) If you can get a hold of an Exacto knife or a cutting blade: Just about anything with a flat edge that you could slightly slide under the transistor to use as leverage.
You're going to also need the aid of a magnifying glass, and unless you're an octopus, you're going to require the aid of a friend to help you.
Here's how to proceed:
Slide the flat edge under the offending Mosfet, just enough that you're able to lever it up. Don't apply pressure yet.
Place the tip of your iron on one of the transistor legs for a few seconds, then gently apply pressure upwards with the blade so that part of the Mosfet lifts up without any resistance. Lift it up clear enough that the solder no longer contacts the leg. Do the same for the other legs of the transistor.
If you encounter undue resistance, regardless of the amount of heat you're applying, then the Mosfet itself has been glued to the PCB. This is going to make it a tad harder to remove.
In this case you'll have to obtain a needle that you can hook into the leg of the transistor, and lift the leg away from the solder joint, not the actual transistor itself as stated above. You may find this method a fair bit harder and you may end up damaging a leg of the Mosfet, so make sure this is the only one you have to replace.
Once all the legs have been lifted clear, place the knife blade under the transistor and try lifting it off the PCB. A bit of brute force may be needed, as the glues used are fairly tough. Unfortunately heat cannot be used to melt the glue, as the stuff is made to be heat resistant.
If all went well and you have the transistor off the PCB, you now have to clean the area for the placement of the new one.
Try to remove as much of the remaining solder from the pads where the transistor was located. Apply a bit of heat on each pad and do a slight brushing to one side, away from the other pads.
Pick a pad that has the most solder remaining on it compared to the others. That's the one you need to solder first.
Get yourself a fairly fine tipped pair of tweezers and use them to place the new transistor on the now vacant pads of the original.
Place the tip of your soldering iron between the chosen pad and the leg of the transistor and let the solder melt and allow the leg to drop slightly and contact the pad. You may have to keep the heat on for slightly longer so you can align the transistor so each leg is approximately over their corresponding pads. If you feel you're taking longer than 3 to 4 seconds for the alignment, then remove the iron and wait a minimum of a minute for the transistor to cool completely. Once cooled, try again.
If all went well, you still have to wait a minimum of one minute for the heat to dissipate completely from the transistor.
Use the tweezers now to put very slight pressure on the top of the transistor. Place your soldering iron, once again, between the pad and leg of the second joint you need to do, and allow it to drop slightly, though depending on the amount of solder on the last pad, this may be limiting. Once again, allow up to a minute for everything to cool.
For the last leg, place your tweezers just above the last leg, but don't make any contact. Apply heat to the pad, then apply slight pressure to the leg so it makes contact with the pad.
You should be done.
If your finished work looks a tad unsightly and the transistor isn't lined up like the others, leave it. The main thing is, if the transistor is making correct contact, then the rest is just cosmetic. I doubt you'll get a PCB assembly inspector with a warrant to enter your home and check up on your work.
I hope the above helps, and please, let me know how you get on.
Take care and GOOD LUCK!!!
Regards,
Relayer [/b]
