Help finding a M0265516 transistor

SLK001

Joined Nov 29, 2011
1,549
Wrong. Look at the 3rd picture in post #7. There is a bypass switch for maximum torque when the trigger is pulled all the way in.
Maybe... Maybe not. I saw the two switches. They looked to me to engage early in the trigger pull, so I thought that they were just "on" switches for the circuitry. Without an "on" switch, the circuitry is always energyzed, so battery life would be severely shortened. Also, he stated that the drill was at 100% speed at any positition.
What's happening now is its running at full speed with %5 trigger and through to %100 trigger.
This statement basically proves that the transistor isn't bad. If the drill is running full speed at all pot posititions, then the PWM is probably running open loop, with no control input. Depending on the design, it can do this if the potentiometer is open. Looking at the first image, the pot looks to be in bad shape.

I have no crystal ball and I have no information on this brand of drill. All I can do is give educated "guesses" as to the ultimate problem given the inputs from the OP. Perhaps your guesses are better... perhaps not.
 

Lestraveled

Joined May 19, 2014
1,946
Certainly this is possible. However, it would belie your original theory that the switch energizes at the end of the trigger throw.
I don't see the logic in that statement. If the mosfet is shorted, the 100% switch will have little effect.

Am I missing something that you are seeing??
 

SLK001

Joined Nov 29, 2011
1,549
I don't see the logic in that statement. If the mosfet is shorted, the 100% switch will have little effect.

Am I missing something that you are seeing??
If the MOSFET is shorted, then it should always run at 100%, regardless of the trigger being pulled or not, IF the switch is at the end of the trigger throw. If the switch is just a circuit energizing switch, then the drill will run at 100% at all trigger posititions once the circuit is energized.

The OP should hope for a shorted MOSFET, since it is an easy fix. If the pot is open, then the whole board will have to be replaced.

It makes no sense that the switch is for 100% purposes, since the MOSFET has as low or even lower on resistance than a mechanical switch.
 

Lestraveled

Joined May 19, 2014
1,946
@SLK001
I see the root of our dilemma. I think that the first switch (5% pull) is in series with the fet/module. The second switch (100% pull) is in parallel (bypass) with the module.

.................It makes no sense that the switch is for 100% purposes, since the MOSFET has as low or even lower on resistance than a mechanical switch.
Then why is there a second switch??

You place your bets and takes your chances.

@Michael Efanow Please let us know what the result is when you change the Mosfet.
 

Thread Starter

Michael Efanow

Joined Apr 4, 2016
14
I'll let you know guys.

The lower spring loaded switch in the housing activates well before the top one. I cannot tell you at what percent trigger it switches at the moment. Perhaps the lower switch engages at low percentage to power the board and then the upper switch bypasses the board for %100. Just theory.
 

Thread Starter

Michael Efanow

Joined Apr 4, 2016
14
The IRF1405 did the job. Drill is working variable speed again.

There was continuity between all the legs of the orginal transistor, but not with the replacement IRF1405. I carefully spent time checking the pot surface with the multimeter, and seemed ok, resistance varied over the track with no noticeable breaks. The pot on the right appears segmented.

I did remove the grease/lubricant from the pot surface to get a clear look. I guess it's non-conductive lube. What could I use? Grease? Vaseline?

Thanks very much for everyone's input. This Bosch drill cost me a few $ many years ago, even though it has older ni-cad technology I didn't wanna give up on it just yet.

Well wishes from Australia.
 

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Thread Starter

Michael Efanow

Joined Apr 4, 2016
14
Also not pictured is the heat sink that mounts on the back of the transistor. I Put some paste on it.

I tried to restrict the chuck to put load on the motor and electrics to see if it could handle the load. Hand got hot and drill kept working.
 
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