Heat kills. There are some guys who think whatever it says, up to thermal shutdown
[eg, 175 degC] is ok, but I don't like my electronics running too hot, or failing prematurely.
So I use the Little Pinkie Test = if it's too hot to hold my little finger on the chip, then it's
too hot. And some redesign should be done. I also have a non-contact IR-Thermometer like Bob.
As Erdin indicated on that other thread, the L293s are bipolar technology, and not MOSFETs,
so there tends to be a collector-emitter drop of upwards to a couple of volts in those parts
[because the output stages have darlington pullup and pulldown ckts], and that times the load
current gives the power dissipation, Pd = Vdrop * Iload. Newer MOSFET h-bridges are much
better.
http://idmax.free.fr/Aide/Stepper/l293.pdf
Also, you might look at the TI 754410 as a drop-in replacement for the L293D. 754410 can go
to 1-Amp load vs 600 mA for the 293.
BTW, one way to tell if an L293 is too hot is, the chip will literally blow up and catch fire. This
actually happened to me once. Not just magic smoke, but the plastic end blew off, and flames
actually came out. So much for thermal shutdown. A mini Boeing 787.