No speedo, odo, wheels not turning on MFD.

On the topic of furnace connectors, my brother has a hot water system that has failed a few times. The first time it was still under warranty, so they came out and replaced the controller board. Everything worked fine for another year or so, and then it failed again in exactly the same fashion. My brother took it apart and examined the controller board. One of the foil runs on the PC board had cracked. He dropped a blob of solder on it and it worked fine for another year, then it failed again.

The problem was once again a foil run, right at the same place. The foil came from a power relay. It was easy to see that the foil was undersized for the current, and thermal cycling from ohmic heating would eventually cause the foil to crack right at the relay socket. The long term fix was to solder in a piece of wire over the existing foil run. The manufacturer could have prevented this problem by using a little more copper at the socket. There was plenty of room on the board, so it wouldn't have cost them any more. It was simply a bad PC layout.

My brother's boiler has been working fine now for years. When he happened to mention the problem and solution to the HVAC person that installed the boiler, the guy said that they had a lot of trouble with that controller card, and all they could do was replace them when they failed. What a waste.

Tom

 

Distressing and common enough. I've used a similar repair method on boards that had cracked due to improper mounting. Not a high density board, just one used for a simple cooling tower PID to control a pinch valve.

Very poorly designed water-tight housing, which the manufacturer supplied. The board was automatically under high stress, combined with a harsh environment and it cracked. Needed a few wires to make it work, but it apparently worked several years after, long enough for them to junk the entire system

And I bet that HVAC guy couldn't give a s*** either. While under warranty, he got paid for it. Off warranty, he charges for the repair and gets paid for it

For example, my HRV is made by Bryant. Has a two speed electric squirrel cage fan. Has failed once under warranty, and it appears to be a standard cheap-nice person motor. Guess what Bryant charges if it's not warranty?

$800

That made my thick muscular neck pulse with anger: would be a cold day in hell I pay that much for a F Bomb cheap motor. You bet I'd make something else work.

 

A little solder can often revive a flaky connector, by repairing a failed crimp connection to wires, repairing circuit board joints (as with the original MFD failure), or by refreshing the mating surfaces with a nice coating of that evil old tin-lead alloy.

 

It might be evil, but tin-lead is good reliable solder

 

I have saved a couple of the speedos taken out of my taxis. Is one of you tech wizards interested in trying to find fault with one?

 

Just curious, though at the moment I'm pretty busy. Have you contacted forum member Hobbit? So far he's looked into inverters, parking pawls, etc.

The next time you have a bad combi meter, could you try this science experiment: remove all four connectors, then plug them back in again. See if the combi meter still works.

If the combi meter is still bad, that disproves the theory of corrosion on the connectors