This is probably the wrong place for this but maybe someone has seen it before?
Should I get 4V (ish) on the motor with the motor supply disconnected?
I have (half) a L293D Quad 1/2 H bridge running a 12V DC motor. My Pro Mini is fed from 5V USB/FTDI supply and is also powering the L293D logic power (VCC1, 1&2ENable and 3&4ENnable Chip pins 1,9 and 16). All grounds are common. A separate 12V supply powers the motor via chip pin 8 - VCC2 . Arduino pins 9 and 10 feed the inputs (10 & 15) on the H bridge. The outputs (11&14) connect straight to the motor. I'm only using half of the chip (bridges 3&4)
With the motor supply disconnected I'm getting 4V on VCC2 - and the motor is trying to turn in accordance with the PWM from the Arduino. Is this normal?
things I've done or noticed so far:
H bridge gets quite hot.
The arduino cannot see the 12V when it is connected to pin 8
Thoroughly checked the wiring -all seems ok.
4v appears on pin 8 with that pin out of its IC socket.
The 4V on pin 8 will stay at 4V with a 470 ohm load to GND
Here's the datasheet