On Fri, 2 Mar 2012 00:52:36 -0500, "John Smith"
put finger to keyboard and composed:

The unit has a very big heat sink, actually I don't recall many that were
bigger.
So I'm not too concerned if thermal overload doesn't work.
No one is going to be injured by a FET going pop, well except the speaker if
the relay doesn't turn off, so my risk assessment is that it doesn't matter
as long as I can get the relay to turn on when the output isn't stuck at a
rail.

I pointed it out because it looked wrong. In fact the design seems to
have too many oddities.

That said, the 4 protection inputs look OK to me, so there does appear
to be a problem with the IC.

There is one thing you might like to try. The TA7317P datasheet
specifies a maximum current of 5mA into pin #9. The circuit as it
stands draws about 3mA through R372. Perhaps you could add a 47K
resistor in parallel with R372. If the voltage on pin #9 rises, then
this would point to an internal regulation problem.

- Franc Zabkar
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