When I run the s/w on my Arduino and motor shield it works OK without external power. As soon as I connect 12VDC to the shield the two output connectors (A and B) of the shield freeze and no longer work. When I disconnect the 12VDC, after a few minutes the shield works again if I do not connect external power. It appears to me that the shield is shutting down because 12VDC is too high, which it should be able to accept. When I connect a 9V battery to external power the shield keeps working, but a 9V battery is not enough to power the motors. Can anyone confirm if this is the case?
I have not cut the external power on the underside of the shield because it is my last shield and when I cut my other shield I believe I pressed too hard and cut whatever was under there as well. This is my last shield until the shops open and I do not want to break it. Can I put a resistor in series with the external power supply to lower the voltage to, say, 9VDC? The current shield is a no-name from China, the shield I broke was a genuine Arduino (tears).