Electronics > Repair
Furnace circuit board repair - How stupid should I feel?
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floobydust:
Fractured solder joints on appliance control boards are commonplace, especially at the large through-hole power components like relays, connectors. Vibration seems to aggravate it so a dryer, furnace blower etc.

In the case of Whirlpool/KitchenAid/Kenmore dishwashers, the boards caught on fire and a person's house burned down. It went to class action I think.
https://www.consumerreports.org/dishwashers/whirlpool-settles-dishwasher-fire-lawsuit-with-offer-of-rebates-and-repairs/

I remember seeing it as due to a bad PCB design, a high-current relay pin had a skinny neck and the connection fractured and overheated. Then the PCB burns and carbon tracks, not enough fault current to pop a fuse- but many appliances rarely use fuses anyhow because of the cost. A 15A circuit is fine with 10A of glowing smoke. Then the door catches fire etc.  But a furnace is a metal enclosure so it would not spread.

I would replace the relay because that pin getting hot can damage them. The furnace control boards failing during winter are a crisis situation and who can really afford that big expense. I keep spare relays for that day.
Paceguy:
Same thing happened to a friend's furnace. The tech from the repair company charged him close to $600 for a new board plus another $180 in labour. The service tech left the board behind and my friend brought it to me to take a look at it. I changed the two relays and repaired the bad melted solder on the connector. Cost: $16 in parts, no labour charge because he's a good friend.

Now he has a spare board for the next time his furnace craps out. Not too many service techs repair boards at the component level. It pays more to replace boards that most of the time are repairable.
floobydust:
Is that what they charge out at, $600 parts +$180 labour to replace a furnace control board? Engineering is cheap in comparison, should been a tradie.
I know during winter they have you by the balls (house freezing cold) so $780 is no problem to charge.

I've fixed so many furnaces for my friends for free, it's usually a dirty flame sensor rod or busted hot-wire igniter. Draft pressure switch is a bit more hassle, draft induction fan motors are easy to change and massive markup on the cheap chinese motor makes it crazy expensive (thanks Lennox!).
BrokenYugo:
In my experience if you clean it up good, wick off all the mystery solder and flow in a good amount of quality 60/40 (or better, e.g. the silver bearing stuff or 63/37) those sort of joints tend to hold up a lot better.
Runco990:
That's a common failure.  I add a piece of solder wick as a beefed up trace.  My dishwasher was the latest casualty.... fixed and fine for years now.
It's all made to fail. 

When I moved into my new house 2 years ago, I made sure to service the HVAC system before winter hit.  A good cleaning, re-cap and check of the furnace board showed 1 bad cap, which caused the fan motor shut down delay to NOT work.  Relays were re-soldered, etc.  Runs like new, for a 35 year old furnace. 

I service EVERYTHING in my house.  2 weeks ago my garbage disposal froze up.  Having nothing to loose.... I took it apart, DE-rusted the metal parts, oiled the motor bearings, cleaned EVERYTHING, put back together.  Runs fine, NO leaks.  My wallet stays closed at least a few more years.   :-+

My take is, it's broken anyway.  Why NOT try to fix it before you order or call for a repair?  Can always do that if repair attempt fails.
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