Defective 1158-110 control board relay?

coldguy23

So I have narrowed down my Beckett AFG's random failure-to-initiate-burner-sequence to a bad control board. I have done this by the following steps:

-Ruling out a stuck or defective limit switch
-Verifying that jumping T-T on the controller works 100% of the time to start up the burner, ruling out the controller and burner.
-Verifying that a call for heat energizes both the white (heat) and green (blower) wires coming from the thermostat (which also powers up the blower instantly every time), thus ruling out the thermostat.

The failure to initiate burner startup sequence has been getting worse since last season, varying from short cycling to complete failure to start, but I think I finally found a bad relay.

Using a mechanic's stethoscope I have identified the relay that activates when the white heat wire energizes. (Which corresponds with the back of the board when I found that schematic online). As you can see below, the relay connects directly to the yellow and blue wires that go to T-T on the controller, however activating the relay does not close the circuit and thus does not power on the burner.



Has to be a bad relay right? What else could it be?

I know you guys probably just replace the whole board but a $2 part and some soldering is preferable to a $150 board for me.

tyvm!!!

109A_5

Hello @coldguy23,

Quite often it is not the relay. It is the solder joints connecting the relay contact pins to the circuit board or the solder joints on the 9 pin connector that you covered up with the colored dots. Inspect them carefully, use magnification if you need to. And since you have the board out inspect the rest of the solder joints too.

And yes the relays are not very expensive.

coldguy23

Son of a b****! lol

How did you know? And how does that even happen- years of thermal cycling? The wiring harness is nowhere near any moving parts.

I resoldered all 9 for good measure.

109A_5

Hello @coldguy23,

coldguy23 said:

Son of a b****! lol

How did you know? And how does that even happen- years of thermal cycling? The wiring harness is nowhere near any moving parts.

I resoldered all 9 for good measure.

Decades of experience. Sadly failed solder joints (in situations like that) are way more common than you would expect.
As far as the reason for the failure of the solder joints at the 9 pin connector, I suspect the metal plating of the pins has a negative reaction with the solder. Maybe joint heating and/or the joint just has too little solder for the circuit current over time.
With the Relay contact pins (in some cases), maybe the same issues and also the relay's vibration too.
In either case once the joint begins to fail odd things can happen and eventually it just totally fails.

Very quick and inexpensive repair if you can do it.
Removing as much of the old defective solder and re-flowing with fresh solder may help with the longevity of the new joint.

I probably would have re-soldered all the relay's connections too while I was there.

Also Relays do fail too, but check the easy, obvious stuff first.

coldguy23

@109A_5 Yeah I had ordered a replacement relay and swapped it out anyway as a preventative thing, although the old one was still working; I also cleaned off the wiring harness pins by scraping off the clear potting/anti-oxidizing spray-on junk with the chisel tip, then fluxed them and gave them a good flow after preheating the joint. Hopefully it will hold another 10 years. If not I know what to look for next time.

In retrospect I would not doubt for a second they intentionally under-solder the joints in order to secure a second sale a decade down the road. There are hundreds of other products out there that are subjected to much greater thermal cycling as well as more vibrations and their joints hold just fine.

Thank you sir!

109A_5

Hello @coldguy23,
Certain devices seem to have a higher solder joint failure rate than others. Connector pins like your case, relay pins and sometimes other physically larger devices and yes places where thermal cycling is an issue. Some of the limited solder thickness may be from the original board soldering method versus hand soldering. Lead free (RoHS) solder for electronics has its own issues too.

I think the conformal coating is to minimize moisture and other environmental contamination problems causing circuit performance issues.