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Jim Katen

Overheating Circuit Board?

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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? 

RIMG0121.JPG

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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 by Marc

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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 by BADAIR

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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. 

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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. 😒

 

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