Repairing a dremel 800 10.8V

[Rorut]

I had to change the power mosfet because the machine did not work properly.
Only worked at full speed. After I replaced the power mosfet one of the three lights is flashing when putting the dremel in "off".
Anyone that is familiar with dremel tools and maybe knows why I got that flashing light. Need to take out battery at the moment when not using it.

Video:
http://sendvid.com/bhv1akyr

 

[gophert]

It looks like either..
A) your new MOSFET is mot turning off completely when the speed selector is turned to minimum.
B) the switch was damaged on the speed selector wheel. Is there (was there) a click when turning the unit off? Did that on/off switch get damaged when you repaired the mosfet? If there is still a click, check if one of the wires connected to the tiny switch on the wheel is disconnected.

 

[Rorut]

It looks like either..
A) your new MOSFET is mot turning off completely when the speed selector is turned to minimum.
B) the switch was damaged on the speed selector wheel. Is there (was there) a click when turning the unit off? Did that on/off switch get damaged when you repaired the mosfet? If there is still a click, check if one of the wires connected to the tiny switch on the wheel is disconnected.

Thanks!
A: how can I be sure if mosfet is not turning off? Measure when connected and in ”off” mode? If this is the problem, is my new mosfet defective?

B: there is a click when entering off mode.
I did not do anything to the switch when changing the mosfet. Do I need to desolder the wheel to see the tiny cables? Wheel is soldered to the pcb with four or five connections, no visual cables what I can see from outside...

Thank you

 

[gophert]

I would just touch the 4 solder pads with your hot soldering iron to remelt in case one cracked or came loose when you were replacing Mosfet.

Your Mosfet could be leaking current. Hard to know without seeing the circuit. Example, turning off could cut connection from battery to motor OR it may pull the gate of Mosfet to Ground.

If your new mosfet is leaking, you could measure a voltage drop across your motor or, if you clip a motor lead and connect your ammeter in series, you can see current flow. Mosfets can be damages by static while handling.

 

[Rorut]

Measuring current in off position I get 2.58mAh
Also 1.2v across the wires

 

[Rorut]

Changed to another new mosfet and the problem was still there. I took electronic cleaner spray through the wheel and now it works. No flashing light anymore