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Overheating Circuit Board?


Jim Katen

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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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  • 4 years later...
1 hour ago, Troyster510 said:

I have a Rheem Criterion furnace with what appears to be the exact same control board. Like yours, my board is burnt around the same resistors. Do you by chance know the part number or have a wiring diagram for that board?

Rheem doesn't disclose the internal circuitry of their control cards. They expect that field diagnosis will end once confirmed to the card as a whole.

If you think it's the resistor, take a good close up photo of it. If the colors are still discernible, I'll tell you the resistance and wattage and you can get one at any Radio Shack.

As  Rheem/Ruud serviceman since the 80's, I seriously doubt that resister is where the issue began. When they begin overheating, the middle lightens to a light brown color (towards the color of thoroughly combusted ash). It doesn't necessarily mean they're bad, they might be just overheated, damaged or simply very old.

You said 'burnt around the same resistors'. That happens often in old cards in the area of resisters more than 1/2 watt in size. It's just the card itself that's burned.

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The damage includes the board itself. I'll betcha the printed circuits on the reverse side are damaged also.

You need a new board. The part number is on the board, along the perimeter somewhere.

Type 'furnace control card #__________' into your search engine. It's how wholesalers find parts themselves sometimes.

Take a photo of the entire card before you begin disconnecting it. It may save you a headache when you put the new one in.

Edited by Marc
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62-22737-08

On the back of the card it looks like a copper strip may have come off the board. My ohm meter can't track where the resistor goes on one leg and I see something suspicious looking on the board. This is also at the worst looking resistor, so if the board was damaged that's likely to be the spot. In the last image you can see an 'L' shaped piece on the board. It looks like a copper strip is missing there. I would love to see the front and back of a good board.

20221115_113814.jpg

20221115_112538.jpg

20221115_202308.jpg

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33 minutes ago, Troyster510 said:

Thank you very much for the link and information.

I noticed that the new card has a different layout for the wires. Are all the labels on the board pretty standard? I want to make sure I have a correct place for all those wires and plugs. I suppose I can compare the Amazon image with my board. 

Yes, sure. New card has upgrades on it but compatibility is still there. If you need help deciphering what goes where, let me know.

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On my board there's a COM and 24VAC.  The COM is the green and yellow wire plug, and the 24VAC is the yellow wire plug next to it. On the new board there is a COM and a SEC, both in a section designated as 24VAC XFMR. I'm assuming that the green and yellow wire plug goes to COM (just like the old board) and the yellow wire plug goes to SEC. Am I correct?

20221115_104229.thumb.jpg.04b1cdbd00e368aae3025afca894a71c.jpg

Edited by Troyster510
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No.

There are two control cables coming in. The small one with just two wires being used is from the outdoor section of your AC system. Heat pumps will use a third wire for the reversing valve. Not everyone uses the same colors on that cable. Just connect one to 'C' (common/neutral) and the other to yellow (Y) unless you have a heat pump. Those two-wire thermostat cables often don't have a yellow wire in them so folks choose something else, usually Blue.

The larger cable is from the thermostat. The colors matter on this cable.

Green (G) turns on the blower. Yellow (Y) turns on the AC compressor. White (W) turns on the heater. 'C' is the neutral connection for the 24 volt supply. The live wire that brings 24 volts to the thermostat seems to be the red wire on your card, which is common. These is the standard color code but I caution you to do two things before you turn the power on for the first time: Take the cover off of your thermostat and make sure the colors at each connections are the same on both thermostat and control card in the furnace. The other thing is to send me a clear photo so I can confirm as well as possible that it's correct.

Edited by Marc
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I think all the small wires will be consistent because I'm just moving them from one board to the other board. I'm just going to make sure the colors are under the same letter screw. I'll definitely send you a photo first though.

The wires I'm asking about are the bigger yellow wires. On the old board the thick yellow wire has a thick green wire with it and it's connected to a screw labeled COM. Right next to that (also on the old board) is another thick yellow wire that connects to a screw labeled 24VAC. Those 2 wires are my primary focus. On the new card, the only remaining screws that appear to be the equivalent place to put those 2 wires are on a set of screws designated as 24VAC XFMR. In that section, one screw is labeled COM and the other one is labeled SEC.

 

It makes sense to me that the thick Yellow and Green from COM on old board will go to COM on new board and that the thick single Yellow wire from 24VAC on old board will go to SEC on new board. I'm just trying to clearly understand where their new homes are.

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53 minutes ago, Troyster510 said:

I think all the small wires will be consistent because I'm just moving them from one board to the other board. I'm just going to make sure the colors are under the same letter screw. I'll definitely send you a photo first though.

The wires I'm asking about are the bigger yellow wires. On the old board the thick yellow wire has a thick green wire with it and it's connected to a screw labeled COM. Right next to that (also on the old board) is another thick yellow wire that connects to a screw labeled 24VAC. Those 2 wires are my primary focus. On the new card, the only remaining screws that appear to be the equivalent place to put those 2 wires are on a set of screws designated as 24VAC XFMR. In that section, one screw is labeled COM and the other one is labeled SEC.

 

It makes sense to me that the thick Yellow and Green from COM on old board will go to COM on new board and that the thick single Yellow wire from 24VAC on old board will go to SEC on new board. I'm just trying to clearly understand where their new homes are.

SEC is the secondary winding of the 24 volt transformer, which supplies the card with 24 volts AC. You should be able to trace those two wires to a small transformer somewhere within the furnace.

Something else to remember. On the card, if the 120 volt supply coming into the furnace from the receptacle is connected backward, everything will work fine but the ignition will try and always fail to ignite. The card knows if the neutral and 120 VAC connections are backward and will fail the ignition.

Edited by Marc
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So if the old board says 24vac and the new card says SEC, which is also 24vac (secondary winding) then it seems like that's the correct place for it. 

The outlet the furnace plugs into hasn't been changed, so I'm sure the hot and neutral are on the correct sides, but I know how to test for that. Thanks for the heads up. 

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41 minutes ago, Troyster510 said:

Marc,

The product on the link you sent me is no longer available. I found this one. I think it's probably compatible.

 

ICM Controls ICM288 Furnace Control, Low Cost Replacement for Rheem 62-24084-82 Control Boards https://a.co/d/aOV65Uq

I don't see where the manufacturer says it's compatible with part# 62-22737-08. As a serviceman, I'd never chance it.

I couldn't find one elsewhere. I could talk to my wholesaler on Monday if you'd like, to see if any of his locations have that card.

Edited by Marc
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