MARQUARDT 2711 DC lithium ion power drill trigger switch

[shockpoint]

Hi team!

(yes tried the search)

New here, and beginner to electronics.

I have come into possession of an old C18 PD (power drill) from Milwaukee. It is an 18V lithium ion battery drill.

The symptoms of it not working are:
- battery connected, trigger pressed, the LED torch comes on but there is no rotation

I have taken it apart and have inspected everything; I have noticed something odd.

The trigger switch is of a Marquardt make, code 2711.9202, which is now out of production but the catalogue shows something similar, 2711.9305.
Here is some information about the 2711 series switches. They are mini potentiometers using mosfets for graded speed PWM control and then at full press, it shorts the motor to battery positive. Datenblatt_DC_Schalter_2711_EN.pdf
Here is a picture of the switch and its markings: https://i.ebayimg.com/images/g/5NwAAOSwalpiaL0L/s-l1200.jpg

While this switch is connected, here are my findings with a multimeter (Dave's famous blue multimeter BM 235)

Battery disconnected
Resistance mode
- while the trigger is not pressed, the leads B- and SB+ (across the diode) are shorted. This short is also present on the leads to the motor, marked M1 and M2, which connect to carbon brushes oriented orthogonally. (reading 0.000-0.001 ohms, bidirectionally across the diode)
- when the trigger is partially depressed, the above is also true.
- when the trigger is fully depressed, the short switches to B- and B+ (which I feel is normal behaviour), and the short disappears from the leads M1 and M2

Diode mode
- when the trigger is not pressed, the leads B- and SB+ (across the diode), read 0.000-0.001V, both in forward and reverse across the anode and cathode
- when the trigger is partially depressed, the above is also true
- when the trigger is fully depressed, the diode, forward bias measurement, reads 0.456V. The reverse direction reads 2.57V

Battery connected
- same as above, but with a voltage measurement across the leads coming from the battery the voltage potential is 0.001V (battery charged to 18.30V)
- on full depression of the switch the difference is 18V across teh brushes and it does jolt the rotor a bit.

I want to say that there is a short, most likely from the diode but possibly inside the trigger switch too (haven't opened it up yet) but I haven't worked with trigger switches before. So I was wondering if anyone could shed light on this as to whether this is normal behaviour. I cannot see how the drill can spin if even at partial switch press there is no voltage potential between the carbon brushes oriented 90degrees to each other.

I can't get my head around the diode behaviour.

Any ideas?

[m k]

Have you tried connecting the input voltage directly to the motor?

Some movements indicate that the rotation controller is not working.

[tunk]

It could possibly be a dying battery, either unbalanced cells or high internal resistance.
Does the motor rotate freely by hand?