Replaced the bad board on my Whisper Furnace. No spark, or gas flow while normally connected but I could jumper the gas valves to 24vac , get it to spark the pilot and heat the house until it was replaced.

The damage on the old board is obvious and looks to be a easy to fix for an emergency spare but I can't find anything useful about the internals of the board. Maybe one of the HVAC gurus has seen this R33 burn problem before on this board.

 

Most of your HVAC guys are working in the field with response time targets, and number of calls per day targets to meet. That usually means that they are trouble-shooting only down to the module level; and you're right...schematics for such things are not as plentiful as they used to be back in the 1980's. That said, you can--most likely--repair the board yourself without a schematic or service documentation, or you may be able to find a "board house" that 'remanufactures' these kinds of units.

R-33 cooked-off for a reason: Too much current.

If the unit is more than a few years old, my first action would be to replace all the electrolytics....no questions asked.
That mylar capacitor, closest to the transistor below R-33, should be tested as well.
Then test all the transistors and diodes closest to R-33 for shorts, etc. , as well as any transformer windings that may be in the R-33 circuit.

Now, that's just looking from the top of the board. Best bet is to trace-out the circuit from the bottom of the board to target your component tests to those components actually in the R-33 circuit. In doing so, you might find that R-33 circuit wanders a bit, but I tend to doubt it. Most likely, you are looking at the root cause of the burned R-33 in the bottom half of your photo.

 

It was a shot in the dark to ask. Into the trash it goes. Tks...

 

Is the new board different from the old board? (asking the obvious question)

 

Is the new board different from the old board? (asking the obvious question)

Yes. It's a Honeywell.

 

Could you find out the value of R33 and reverse engineer and test the components around Q4?

 

Could you find out the value of R33 and reverse engineer and test the components around Q4?

Sure I could fix it given time and motivation. I was hoping for a shortcut. Tks for your time.