Just finishing up putting together a new MendelMax 2. I was hesitant to go with the Rambo because of the amount of work it would take to replace anything, but it's a nice package so I went for it. I had my X and Y axis working fine, but when I ran the Z axis the first time I realized I had one of the Z steppers wiring reversed because they were moving in opposite directions. No big deal, I just swapped the wires for on of them so that they both match. Upon plugging them back in, I had 0 movement. The steppers don't even activate. Plug them into the X or Y driver and they work fine. Plugging any other steppers into the Z axis and those don't work.

Somebody please point out something I might be missing. I didn't unplug the power when I detached the motors from the board, not that I've ever had a problem doing that before. I am hitting myself over the head now.

If you detach the motor while it is powered, the driver will most likely burn. Always do power down stepper drivers before making any changes to motor wiring.

....... if it worked fine before you did the un-plug and broke immediately after - that's a pretty good indication.

Like ^^ said, power down before doing wiring changes. You *can* get away with it some times on some things. You can't get away with it all the time on everything. You will not hurt anything ever by unplugging it with the power off.

You think you were getting away with it probably because after 30 sec or 60 sec with no movement, most firmwares would change the enable line, which turns off the driver outputs to conserve power. Because steppers consume most power when standing still. So even if the drivers were powered on, drivers outputs were off, so the motors coils didnt had any power through them at that time. Otherwise most likely would of burned then. Btw most sender programs have "motors off" button. But its much safer to turn off the drivers completely.

Yup, I was being hasty and careless. Anyway, does anybody know a source for replacement A4982 chips? Digikey seems to be out and I've had no luck anywhere else.

Looks like Digikey and Newark are the two stocking distributors. Neither one has the QFN. If you are not experienced doing it, pulling a QFN off and replacing it is most likely to fail. I know I would not try it without the right kind of gear. Getting the solder to properly reflow on that thermal pad is not easy.

The 32 QFN for that part isn't available in the US right now from distributors. I was going to build a batch of boards last month but couldn't get that package. Digikey says they'll have stock after the first of the year. You can get them in Shenzhen but they know they are scarce. I've seen them for about US$10 over there from sources that have reputable parts. To replace one you'll need a hot air rework station and the ability to be able to do it. Not for someone that hasn't done it before but then again, you have to learn sometime. Though this wouldn't be the part I'd want to learn on...

Around work, that's a package we don't let the new kids do the rework on. Even with a trained operator, the results are not as good as one would like.

How about switching over to a Ramps? ....

Stoof, contact info@ultimachine.com and they will rework it for you.

Related question (I hope)? I am building my second reprap with a rambo using a 24 volt p/s. Since I want to limit the amount of damage if I discover something about the 24 volt under fire, I wanted to get my hot end and bed working without the motors connected (foolishly or not, I figured that might protect the motor drivers). I knew as mentioned above not to unplug the motors under power. My question is.....what about powering up the rambo with no motors conected (or maybe one for the extruder)? Is that likely to cause problems even if I don't plug anything in under power?

Charlie RC

There should be no problem with plugging in the board without motors attached. Of course there also should be no problem with plugging it in with motors attached if it's all set up right. If it's a Ramps style board (rather than a Rambo) Make sure the motor driver boards are not plugged in backwards. They will fry regardless of motors if the are in wrong.

Edited 1 time(s). Last edit at 11/24/2013 10:50AM by uncle_bob.

Anyone doing new designs should consider adding TVS diodes on the motor outputs to reduce the chance of frying electronics if you do make the mistake and plug/unplug your motors with power on that'll help cut the induction spikes down to something less likely to fry the drivers.

Quote
charlieRC
Related question (I hope)? I am building my second reprap with a rambo using a 24 volt p/s. Since I want to limit the amount of damage if I discover something about the 24 volt under fire, I wanted to get my hot end and bed working without the motors connected (foolishly or not, I figured that might protect the motor drivers). I knew as mentioned above not to unplug the motors under power. My question is.....what about powering up the rambo with no motors conected (or maybe one for the extruder)? Is that likely to cause problems even if I don't plug anything in under power?

As mentioned by others, no problem.

If you have an older version of RAMBo with PTC fuses (orangey-yellow blade-like components), replace the 11A PTC fuse with a proper fuse before moving to 24V. The 11A PTC fuses are only rated to 16V, and can cause all sorts of issues at higher voltages.

With the motors, always a good idea to test them with a multimeter before you plug them in the first time. Had a friend buy 5 motors, and after plugging them in his Z stepper died. Turns out one of the Z motors had a shorted coil, and this took out the driver (it was a RAMPS board, so it was an A4988). The resistance of a stepper motor coil should be low, but it's unlikely to be less than a 1 ohm (usually listed on the spec sheet), and a stepper motor has 2 such coils. It's a simple test that avoids costly driver replacements.

While you are ohming out the motor windings - wiggle / (gently) tug the wires on the motor connectors. They occasionally don't get the wire stripped quite right. The net result is a motor that only connects sometimes. It's rare enough that it's only worth checking if you have a meter on the wires for another reason.