Jim Katen 138 Posted June 14, 2018 Report Share Posted June 14, 2018 I can't recall having seen this before. It's a 1993 Ruud gas furnace. The circuit board is toasted at the upper right corner, behind all of those resistors. Any idea what's going on here? Quote Link to post Share on other sites
Marc 83 Posted June 14, 2018 Report Share Posted June 14, 2018 (edited) The light-blue colored cluster of 5 resisters are rated 1 watt each but the 6th one at the lower right is higher than that, perhaps 5 watt. Just got too hot. Background heat may have been a factor also. Design should have provided for longer leads on those power resisters to put some space between them and the board. That's a fiberglass board, I believe. Edited June 14, 2018 by Marc Quote Link to post Share on other sites
BADAIR 14 Posted June 14, 2018 Report Share Posted June 14, 2018 (edited) last fall during a severe rain/thunderstorm with lightning i was walking by the furnace closet when the room lit up from a very nearby strike followed by a loud bang from the closet and the odor you'd expect from burnt electronics my tech showed up & showed me that it blew a board and a relay i couldn't recall if the unit was operating at the time of or not, was a question he asked i've also seen when evap spillage occurs from our upright a/c over furnace configurations moisture ruins resistors & the next time it fires there ya go option 3 stuff happens Edited June 14, 2018 by BADAIR Quote Link to post Share on other sites
Jim Katen 138 Posted June 15, 2018 Author Report Share Posted June 15, 2018 Rheem/Ruud put their circuit boards inside metal enclosures in the blower compartment, which protects them pretty well from moisture and dirt. I suspect that it is, indeed, heat from the resistors, but it seems odd. I've looked at thousands of these things and never seen discoloration from resistors like this. I find myself wondering if this is a slow-moving failure in progress. Quote Link to post Share on other sites
John Kogel 35 Posted June 15, 2018 Report Share Posted June 15, 2018 You have a good eye and a good camera, Jim. My hobby is old radios, so I've seen plenty of scorched parts. When a resistor gets hot, it usually is the result of a failure in another component that is being supplied by that resistor. So the fix there is not to just replace the scorched resistor, but to find the bad component that caused the scorch. And the modern repair for that is a new circuit board. 😒 Quote Link to post Share on other sites
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