[coloradonewbie]

I let the smoke out of one of my Wantai stepper controllers the other day and I need help identifying the cooked resistors I found.

The two resistors that look cooked are tan in color and marked
0.22 ohms with a 2WJ on them also.

Is this a .22 ohm 2 Watt 5% resistor I need?

I'd like to replace them and see if I can bring it
back to life.

I know about nothing in the electronics field. I can wire the
stuff together and solder a bit and that's about it.

What had happened to the stepper driver is a connector on the
Y motor came apart enough to let it spark inside. It didn't short
to ground, it just interrupted the current to the motor while it
was running a program. A little smoke from the stepper driver
and that was it. Power supply wouldn't work with the driver
connected. Worked fine if it was disconnected.

Any help with this is greatly appreciated.

Thanks, Pete

[Al_The_Man]

If the value and wattage is printed on them then there is every possibility that they are wire wound and the value you assume.
Wire wound do not change value so easily as composition type when subjected to heat.
So replacing them may not cure the problem unless they are open circuit.
If you need replacements, Digikey carry these type.
It sounds like you may have shorted a power switching component.
Al.

[coloradonewbie]

Thanks Al,

There are 2 sets next to each other on the board. Same values but the smoked looking ones are open and the other 2 have resistance. I figured it was worth a shot to find out if it fixes it. I could not find any other discoloration on any other components on the board. There are a lot of tiny ones that may be bad, but nothing obvious.

I'll try Digikey,

Thanks again.

Pete

[Torchhead]

90% chance the driver FETS on that pair are toast. Power resistors don't just burn out. They are the current sense resistors in the source legs of the FET's. If they burned up it's like having the tires burn on your car (after to plunged off the cliff). An effect , not a cause. Usually you lose both upper and lower FETS on a leg (H-Bridge configuration). If two resistors are burned then both legs on one side or one leg on each H-bridge is gone. The fact your the drive loads the power supply indicates there are shorted power components. The resistors just acted as (poor) fuses to keep the board from completely melting or bursting into flame.

Sorry to be the bearer of bad news. Plan on replacing the drive.

TOM caudle
www.CandCNC.com

[coloradonewbie]

Thanks torchhead,

I've already replaced the driver, or should I say Wantai Motors
replaced it. I just got the new one and installed it on my table.

I just opened the old drive to see if I could see what let loose
when the connector came loose. Both resistors are on one side,
the other pair of resistors on the other side seem to be fine.
I was just wondering if I could get the old driver to fire back
up by replacing $.70 worth of resistors.

I know what you're saying about the power supply sensing
a direct short. The open resistors wouldn't do that. I guess I'll
just send it back to Wantai and see if they'll send me another
one. They said they would.

The Wantai stuff works great, it was totally my fault, I knew
about the bad connector but was so excited to get the
new electronics on the table I spaced fixing the cable correctly.

It's up and running again now, lesson learned.

Thanks for all your help folks,

Pete