A4983 (no voltage reg): 1A/B outs full VMOT when stepping

Hi there…

I got the smaller A4983 stepper driver board. I got it to work correctly on my breadboard… no problems!

Yesterday I plugged it on my prototype PCB. All connections are the same as the breadboard, but for some reason my stepper motor didn’t move this time.

I measure the voltage on the 4 motor pins, and for my surprise, 1A and B was 11.75 Volts (I got a 12V supply, so it seem to output 100% of the power on those pins) and 2A/B was 0V statically, no matter what I did to the STEP pin. Does this indicate the A4983 chip is burned? or does it indicates some other problem with some other component on the board?

The A4983 chip is not getting too hot, as I would expect in case of being burned.

I’m asking because I’m trying to determine if the chip is actually OK, and if so, I would try to replace the actual burned component. (unfortunately I don’t have an oscilloscope, in case you ask… Just a simple multimeter!)

Any tip would be really appreciated!

all the best…



The problem is not immediately obvious to me. Do you have the board socketed? If so, can you unplug it and plug it back into your breadboard circuit and see if it still works there? If not, I would just measure all the pin voltages to make sure you have what you expect on them.

- Jan

Did that. Same result. I measured all pins voltages, and all seemed fine, exactly same values as the other boards I have ( got 4 boards, 3 with voltage regs(md09a) and this one without it (md09b).)

If I replace that md09b by a good md09a on the breadboard (no circuit modification), it works just fine!

Do you think I should measure the voltage on each pin of the A4983 chip too?

I was examining and comparing the schematic diagram of the md09a and md09b, but one thing I couldn’t find there… the trimpot that regulates the vmot current… Are those schematics fully updated?

last question: As I can’t find an md09b to buy, I got 2 new md09a from robotshop.ca (I’m in Canada)… do you think would be safe for me to replace the A4983 chip on that faulty md09b? I’m asking because I got my custom Reprap RAMPS board all build up onto am arduino mega protoboard and I don’t have extra space on the board to fit a forth md09a board… so frustating that my only md09b got broken… the board was so nice and cute!!! LOL

thanks in advance…


If the other boards are working, your non-working unit probably is damaged, and it’s probably not worth trying to swap the ICs. We’re starting to ship backorders on item 1201; if you order now, we would likely ship by the end of next week. (Also, some distributors that backordered more with us than they had orders for might have some stock sooner that we would be able to ship an order that came in today.)

The trimpots are shown on the bottom left of the schematics for both products.

- Jan

Ok… good to kown… I’ll place an order with robotshop.ca then so I don’t have to pay customs.

I saw then now… R9 and R7!
What’s the specification for it? I managed to over-rotate one on one of the 3 working boards (3 ones with regulators) and it is physically damaged now. The board works just fine, but outputs minimum current to the stepper. (it goes to 100% current if I physically press the trimpot with the screwdriver)

It’s fairly straight forward to replace that trimpot, I just need to known the specification to get a new one… (I’m not very electronic savy guy… learning as I go… =\ )

Or maybe I’ll get the one from the damaged md09b board then and switch it on the working one. they should be the same specs right?



The pots on both products 1201 and 1202 are 10k Ohms.

- Ryan

thanks a lot!