hobbycnc board

[wjbzone]

I started my cnc project by buying the Hobbycnc board. I got the unassembled board and put it all together. Dave, from Hobbycnc was very helpful in getting it up and running. For the most part I have been very happy with it.

I had no experience in putting these boards together, and I learned a lot in doing it. I can now troubleshoot my board and usualy solve problems.

I think most of the problems I have had are due to my own inexperince and soldering techniques. Mostly loose connnections.

One reoccuring problem I have is that one of my UNC5804B IC chip burns out. Three times now. It is cheap to replace ($4.50), but I don’t know why it is happening. Dave, from Hobbycnc told me a loose heatsink on the IC can short the pins. That may have been the cause, but this last time I had it on tight.

Just wondering how if anyone else has put this board together and how it is doing.

Bill.

[jimini]

Hi WJB Im using the same board with about 1 amp motors and have no problem.
I do have a fan drawing air from the chips.
I've had it running for a couple of hours at a time,and it works flawlessly........................................Jim

[wjbzone]

Jim,

I usually run several hours at a time with no trouble too. I hate when it messes up at the end of a two hour job.

I am running the 125 oz-in motors (I think they are 1.25 amp). I also have a fan drawing air from the electronics box.

The most trouble I had putting this together was the 6 pin connectors that plug my motors into the box. If I have problems thats the first place I check. I don't know if that connection could have caused my IC's to blow.

I think I am going to eliminate the plugs and use some terminal blocks. Also I am going to solder the UNC5804B IC directly to the board and get rid of the IC sockets. (the socket melts when the chip burns up)

Bill

[jimini]

Wow they must get HOT! I have my wires in a terminal block so maybe, like you say, that's the answer...........Jim

[wjbzone]

I looked it the box through the fan hole last time it happened. I could smell it burning. There was a flame shooting out the side of the chip looked about 3/4" long. It blackened the Diode next to it.


It's blackened the diode before, it all worked fine when I replaced the socket and chip.

Its always the same two pins that are burned out.

Bill.

[pacosoide]

If you are repeatedly burning the same chip, you may have some component drawing excess current from it. Measure the resistance from the pins to the positive of the power supply. See if there is a difference between that measured resistance and a similar pin on the other 5804 chip. Maybe your stepper is the problem, maybe the limiting resistor. All things considered you are cooking the chip because there is too much power drawn from it beyond what it can dissipate. Joe.