Help with an elliptical exercise machine controller

[vinito]

Anybody feel like helping me troubleshoot a controller board for an elliptical machine?

I've put the word "resistance" in quotes when I'm referring to the mechanical resistance the machine creates to help avoid confusion between that and Ohms flavor resistance.

It has a "resistance" control, which mechanically is a drum of magnets that is brought closer to or farther from a flywheel drum. The adjustment control has essentially a radio-control servo type thing, i.e. it's a 6V DC motor geared down for very high torque (much larger than an RC servo, but essentially the same function). Then there is a potentiometer attached to feed back position.

What's happening is if it's mechanically set for high "resistance" on the flywheel (magnets close) you can push the <down> button and it will move the servo, pull the magnets away in a controlled way (i.e. will move it one step at a time as per <down> button pushes) until it reaches the "low resistance" end of the travel. Thus the potentiometer is working properly and even the motor works properly going the one direction
So far so good.

The problem is that if it's low and you ask it go increase the flywheel "resistance", it doesn't function for that direction. I connected a multimeter to the motor leads coming from the control board and it does switch back & forth between +6V and - 6V if I manually move the potentiometer. So the controller seems to be sending appropriate voltage in concordance to the pot setting.
I suspected it isn't sending enough current. So I hooked up to the motor leads a bench power supply set to 6V. First I moved the motor back & forth manually. It works fine. Then I hooked it up in parallel to the leads coming from the controller. If I set things so it wants to move the potentiometer in the problematic direction, with the additional current of the power supply set just barely high enough to move the motor, it does move the motor until it hits the proper position, then the controller sends the opposite polarity down the motor leads and stops the motion. i.e. the additional current boost from my power supply hacks the setup so it will move the motor in the problem direction until it hits the target position, then the controller flips polarity on it's motor leads and this stops the motor. I am of course immediately unplugging things at this point to minimize the fight as much as possible.

OK that's not a very clear explanation of what's going on, but it's about the best I can do.

So anyway, I suspect there is a transistor on the controller board that is faulty and isn't amplifying current properly in the problem direction anymore. Am I on the right track? There are some through-hole transistors that are possibly the culprit, but I thought I'd try to see if somebody felt like holding my hand on this first. I'm pretty green on this electronics stuff. I can take some photos of the board and such if somebody wants to help me troubleshoot this thing. In fact I'll do that anyway, and label the wires and such, then upload it here. In the meantime, a yay on offer to help will inspire me to keep poking on this thing.

There doesn't appear to be any obvious magic smoke prison breaks.

Thanks for any help.
Sorry my articulating is so clumsy.

[vinito]

Never mind for the non-help. I figured it out.

[cs.dk]

Then post the solution. It could be a help for others in the future.

Now the topic is just trash

[vinito]

I posted the question and got zero replies after two days. Note that you didn't offer any thoughts on the actual electronics problem either, just about how bad my post was. It was trash already apparently. I deleted the board pictures to save bandwidth since nobody seemed interested anyway.
Any replies from knowledgeable electronics guys would have been a lot more informative than anything I could offer, and might have helped me out even. Heck, I might have learned something.
The solution was the wall wart. Is that educational? I don't know why a degraded wall wart would allow one direction to work and not the other.
Feel free to speculate about that if you think it might help anybody.

[PlainName]

got zero replies after two days

It's Christmas and people aren't at work (so can't visit EEVBlog on the sly without their familial partner throwing a wobbly). Besides which, the internet is a large place and people have things to do with their lives, so may not get around to your post for some time.

And, often, people see something but don't have an immediate clue so don't say anything. Doesn't mean there isn't any interest, just that they're not filling up the place with pointless 'not a clue' posts.

Maybe fuel there for a New Year's resolution?