Motor Shield - DC motor output broken

[theborg]

My motor shield was working well for a while for various projects, but recently it doesn't seem to be working as expected. I can only drive a DC motor properly off port M2, the other ports seem broken.

I set up a simple test program to configure M1 through M4 as DC motors and run them forwards for three seconds and backwards for three seconds, in a loop, while I manually check each port for voltage with a multimeter. I'm using 4 AA batteries wired to the external power block (about 5.25 volts), the Arduino running off USB, and no jumper. For the test I don't have any motors wired up. What I get is the following:

M1 - no volts
M2 - works perfectly - ~ +4.7 volts and -4.7 volts every three seconds
M3 - no volts
M4 - -4.7 volts and 0 volts every three seconds

Any ideas what might be causing this? The board looks good - no visible damage or burn marks, green LED shines fine, and it used to work. Not sure if I fried something but I've never put any serious loads on it.

[adafruit_support_bill]

It is possible to fry the L293 chips. (That is why we have sockets for them in the kit!) Some small motors can pull surprising amounts of current. You might consider piggybacking two of them. That will nearly double the current handling capacity.

[theborg]

Thanks for the fast response. I didn't get sockets with my motor shield kit but it's almost a year old (May 2010) so maybe the sockets are new to the kit. I'll take a crack at desoldering out the L293s and putting in sockets and a new pair of drivers, hopefully that will work.

[adafruit_support_bill]

Yes. I think we started shipping them with sockets last summer. The easiest way to desolder those with a standard soldering iron is to clip all the pins and desolder them individually.