Harman P68 Control Board Burnt

[Darfyjones]

I have a strange issue with a Harman P68 control board burning up on the fuse connector. No other component on the board looks damaged at all. The fuse itself remained intact and still has continuity. Igniter has no sign of damage or arcing, 50 ohms of resistance when cold too. I assume there's a short somewhere but it wasn't enough current to trip the breaker.

I'm going to replace the board at the very least but wanted to know how to test the motors for faults. Don't want to spend a couple hundred bucks and run into the same issue.

Any help is appreciated

 

[jackman]

Welcome to the forum. I have a few thoughts. Knowing the history of the stove may help. Does the stove still run with the burnt board? Is it the correct fuse? If so, I'd plug the board in and use a multi-meter to measure the current thru the fuse. I'd also test each of the motors, combustion, distribution, and auger, and measure the current of each to make sure they're working and not drawing excessive current. You may have to make some test leads to make the connections.

I wouldn't put the new board in until you're sure the new board won't get cooked.

 

[Darfyjones]

I do not know much about the history of the stove. It was gifted to me by a work friend who said it worked last time they used it and was serviced just before putting it in storage. They used this stove as their main heat source before replacing it with a heat pump system. The stove ran well for me until now with some minor issues from a power outage. Things like the intake motor running long after it has been turned off and the room temp probe being inconsistent. I have already tried a new ESP to address that particular issue but no change, but a new board is in order regardless.

There were no diagnostic LED codes or other warning signs of failure. While I was at work my partner turned on the stove with auto ignite, the auger, intake and igniter kicked on like normal but there was a strong smell. We turned the stove off before it could ignite but didn't unplug it until I got home.

The fuse is a 250v 6 amp. I was pretty sure that was correct but doing some quick research Harman suggests a 5 amp. I removed the igniter and plugged in the stove. No sparks or smoke from the board and it ran the intake motor and auger like you would expect. I didn't let it run any more than 15 seconds before unplugging it.

What sort of specs should I be looking for on current draw?

 

[Mt Bob]

Not uncommon in any electronics, usually means the fuse holder was poorly soldered in. Just seems to me there are more problems with poor solder joints ever since gov. mandated lead free solder.

 

[jzm2cc]

Possibly poor connector tension on the burnt side of the fuse or bad solder joint at Mt Bob mentioned. Either way lots of heat generated thus burnt board smell. The solder appears to be missing on bottom of board. Possibly pinching connectors together to increase tension, and clean up interface to fuse and resoldering connector might stop elevated resistance/heat issue. If so good to know before you opt for
another new board.

 

[Darfyjones]

That's a good point about the solder joints. I did notice the fuse holder on the burnt side let the fuse rest inside rather than hold it tightly. I'll resolder the connection and fix the tension and test that.

 

[Darfyjones]

I resoldered the fuse holder and bent it to hold the fuse more securely. I removed the igniter and was able to run it for a whole day with no issues.

My guess is like what Mt Bob and jzm2cc said, the solder gave up or the fuse holder barely touched the fuse. When the igniter kicked on it had high resistance up to the fuse but not through it, which may be why it didn't blow.

Thank you all for the suggestions, you've been a huge help. Perfect timing too since it's going to hit -20 for me this week.