Welp, it was a completely different looking board when the guy brought it in, so I resigned myself to paying out the nose. The price he quoted me included the service call(s) and installation, so I feel better about it. This furnace is so damn old... (how old is it?!!) and as I mentioned, there was no way to get at the board in the 140 degree attic without suffering. Also no way to get it out without disconnecting some wires. All's well that ends well, he did a good job.
A lot of new appliances have diagnostic ports - my fridge died a few years about, about 20 milliseconds outside of warranty I believe. guy plugged a tablet into the port on top of the fridge, said it's the condensor fan and replaced it. $100 fan (basically an over-sized computer fan, must be worth about $14.99. After all the surcharges & visit fee it was $400+.
I should get a port reader before it dies again.
