DC Motor stutter problem(not stepper)

[thejimmy]

Hi everyone. I have this problem...obviously. I have a cordless screwdriver that I am trying to fix as I am trying to learn about electronics and motors. I am a carpenter and I found this nice cordless screwdriver at the scrapyard that I want to fix to use on other electronic project. The motor works and all the lights come on when I plug it in to the relative voltage. When I opened the screwdriver it had 4 Ni-Cd 1.2v AA 700mAh batteries connected in series. Which is then 4.8 volts right? But still 700mAh? The batteries are dead as doornails so I want to bypass the batteries by just using a 5v adapter but the motor turns a few turns then stops when I connect it directly to the dc adapter. Why is this? Am I using the wrong Volts? The motor is a very small brushed motor that fits into a gearhead. I am uncertain what volts and amps to use. I tried different ones all in the 5 volt range with different amp values from 500mA to 2000mA. The 2000mA 5v adapter turns it the most but stutters. Less amps don't work at all. Also I opened the motor and the brushes seem fine as well as the winding. No burns or dark marks. I'm kinda out of ideas as to what the problem might be...HELP? pls

 

[73's de Edd]

Reads like you covered all bases except possibly the REAL current needs at dead startup.
Place clipped in DC voltage monitoring across the supply and then do a finger boosted chuck rotation during initi
al start up and see if the voltage then pulls down excessively.
Expecting it to then run . . . .unloaded.

73's de Edd . . .

 

[davenn]

Which is then 4.8 volts right? But still 700mAh?

the 700mAH is only an indication of how much can be drawn off the battery for a certain time .... ie. 700mA for one hour

As Edd suggested, the startup / full load current can be much higher, it could easily be as high as 3 or more amps
A battery can handle this but a fixed 5V 2A PSU cant handle that initial high current pulse