Furnace troubleshooting?

Our house has a 10-yr old gas furnace that I've been having some problems with & was hoping there might be some HVAC people here to help guide me.

I don't know what brand it is, the only markings are "The Dependable 92" on the door. I'm getting a Flame Sense error according to the LED pattern on the control board. I've cleaned off the sensor with scotchbrite to no avail, and measured voltages - but I have no idea what they should be.

I have a steady 40v ac applied to the flame sensor at all times, as well as a -5vdc. When the burners ignite, the ac voltage stays the same, but I read a -10vdc. Does this sound normal?

I'm figuring at this point it's either the sensor or the control board, as I previously had to rewire the sensor due to a bad pin in the molex connector.

Any words of wisdom?

No HVAC folk here?

Goodman? Janitrol? I'm not a HVAC guy, but I fought a fight *(and won) with the furnace in my last house.

The AC is applied to the flame sensor. When the ignitor lights the burner the flame actually recitifies the AC to a small DC. Googling tells me that it makes a DC current something along the lines of 10 mA. Not sure what your DC voltage reading should be with or without flame.

Is there an owners manual down in the bottom of the furnace? It might have a schematic.

http://www.google.com/patents?vid=USPAT5437263

might help some