I have a 4V Li-ion Screwdriver by Master Mechanic and it's been super handy for the past 5 years. Recently, I've been having problems where it occasionally stops rotating properly when I press the trigger. It still turns, but slowly, weakly, and only for a second. This usually only happens when a screw is already on tightly, back when the electric screwdriver was still functioning properly. It's fully charged, and not in the lock position either. Most tutorials online I've been able to find are mostly for battery replacement but mine seems to be working. Any ideas what might be wrong and how I can fix it?

  • Your planetary gears may have broken off a tooth or two over the years. If the busted gear bits get caught between inner gears and outer ring, they can cause jams. Take the rotary gear apart and look for busted teeth. Most electric screwdrivers use a two level planetary gearbox, so there are two levels of 3 gears each to check. If you've got badly stripped gears, save the planetary unit for your next screwdriver. The gear bits are often interchangeable, and that way you'll have spares. Apr 13, 2017 at 0:20
  • "Locked in over torque mode" There is actually a switch on your tool you can set to improperly over tighten something?
    – Alaska Man
    Apr 13, 2017 at 16:59
  • @Alaskaman I do the odd DIY jobs around the house here and there and assemble Ikea furniture, but that's about it. I don't have the terminology to describe it accurately, but no, this isn't a setting on my screwdriver. I'm trying to describe what happens when the rotation of the screwdriver slows down when the screws are wound tightly enough (I assume for safety reasons/prevent stripping the threads).
    – Alex
    Apr 14, 2017 at 18:53
  • @wayfaringstranger Thanks for the tip! I'll check that out
    – Alex
    Apr 14, 2017 at 18:54

1 Answer 1


I suggest checking the battery anyway. 5 years on a rechargeable might need to be replaced. I have a small B&D like that that the battery is just gone far enough it will do light work, but nothing heavy anymore.

  • Great point, I may as well check the battery while I'm at it. Thanks!
    – Alex
    Apr 14, 2017 at 18:55

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