My reason for jumping to it being a contact in a relay going bad is the way the mechanical portion works.
It uses the same joints and mechanical connections to go up as down. That makes me feel a connection in that group would be as balky and slow to move in one direction as another.
But the motor which moves it in both directions, gets power from two different routes for up versus down!
Basic idea on this type gizmo, is that a DC motor runs in a different direction if we reverse the polarity of the DC power it gets. Normally it runs as well in one direction as the other.
If the motor has to work too hard to move the chair, I would expect it to draw much more current and blow or trip a fuse or breaker.
My thought, on this sofa is that there are two relays of the same type that are used to control the power to the motor. With them both the same relay, if we swap the relays, it tells us some good stuff about the relay condition.
If the problem is solved on one movement but the other movement is then bad, we can say it is a bad relay!
But if swapping the relays leaves the same problem, we then need to look at other things like a bad switch. I feel it is not the switch as the movement does happen, just not at normal speed. More testing needed!
One way to get slow DC motor speed is to give it lower voltage and that is what we get if a contact in the relay is corroded or burned from arcing! Feed a 12VDC motor 11.5 volts and it runs slower!
But that is all very much based on theory and I'm always alert to my theory
being wrong until tested!
There may be a rabbit on a treadmill and he's just tired of running uphill!
I hope we do get a good solid report of what they find as I've never looked under this type sofa!
What I fear is that they will get a report that goes something like, "We don't repair sofas! A new one is only $1400!"
We tend to throw a lot of good stuff in the trash becasue a $5 relay goes bad!!
