[keebler303]

My x axis fuse for the DC side (FU12) keeps blowing. It blows as soon as I turn the machine on. Anybody know where I should look for trouble? could it be a shorted transistor? It doesn't sound like that would blow the fuse but it might.

Thanks
Matt

[NC Cams]

After paying a small fortune to watch a CNC repair guy, here's what I learned:

Get a fist full of fuses and start unplugging stuff in the X axis circuit. When you quite blowing fuses, you found the root cause of the problem.

Simple process of elimination (which anybody could do if they can read a schematic of the wiring) was the way the high priced help found it...

If it is a driver card, especially one with ah H bridge in it (typical way they reverse polarity on DC drives) a shorted bridge would essentially shunt DC + straight to DC- and toast fuses almost immediately. Ditto that if a Schottky protection diodes in the drive short.

First thing to do is remove the power feed to the servo amp on that axis. If that solves the problem, figure on having the amp serviced... otherwise, keep hunting...

Contact me off line so I can send you my bill for consulting - no matter what it is, the amount will be cheaper than what it cost me to learn that exact same lesson....

[machintek]

Fuse 12. Must be a BOSS 3 through 6. There is a lot on that circuit, including a bridge rectifer, transistors, and diodes. Any one of those could be shorted. But all of those are semi-conductors which means you can look for a voltage drop across the junction. If no voltage drop, it may be shorted. Reverse the test leads and see if it still conducts. Process of elimination.

George

[split63]

My x axis fuse for the DC side (FU12) keeps blowing. It
Matt

The X-axis drive board pulls current through the stepper and through FU12. Those boards are on the back door panel of the control unit. Try swapping the X-axis drive board with the Y and see if the Y-axis drive fuse blows (FU13). If so, you have a bad X drive board.

If it does not follow the board then look to the four transistors that are mounted on the door (Q1-Q4) for the X-axis, one or more is probably shorted.

:cheers:

[keebler303]

i found the x5 wire to my SMS board was broken off. looked like a cold solder joint that vibrated loose. could this be causing my problem? I will fix it and try again. I swapped the x and z boards and the x board works in the z so its not the board. working on pulling out the transistors now.

Matt

[keebler303]

it runs!

I reconnected the X5 wire to the SMS board and I found the root of the problem. Atransistor was shorted, externally. the common wire that runs between the four transistors had arced to one of the other pins on the transistor. I was getting ready to pull them out when I noticed a little spot that looked like it had arced. I got the leads bent away from each other and it runs now.

Thanks for all the great help guys.
Matt