How to repair damaged Driver Boards/Cards

[edd]

Has anyone tried repairing a damaged Driver Board. I am on my thrid Y-Axis Driver board; at 225.00 a shot it is getting too expensive for my High School Shop Budget. The components for one can't run more than $30.00. It would save alot of time and money if I could isolate the bad component, remove and solder in a good one.
Has anyone tried doing this??? Any ideas.

[danhamm@abccom.bc.ca]

Yes! the SLA7026M transistor and maybe the 47ohm
5 watt resistor, the best method of removal is to snip the legs of the transistor, and remove them
1 by 1 so to not overheat the foil on the board,
after you have removed the transistor and resistor, check the foil on both sides of the board for continuity, jumper if required.
Allegro is the supplier,they are a popular power
tran, about $12.50 ea.

[Greg Gressel]

I just fried the SLA7026M transistor on my x axis. Earlier in the day I upgraded my y axis from the PK266-02A (2 amp 1.8 ohm) to the more powerful PK268-02A (2 amp 2.25 ohm) stepper. After hooking the new stepper in I tested the motor and it worked great. Later when I tried to move the x axis, pop and a puff of smoke from the transistor. My questions:
1) Would switching the 266 to the 268 cause another axis to burn the driver board.
2) Any other ideas on why this would decide to overheat and pop?
3) If I replace the transistor and/or the entire board is there a troubleshooting sequence to prevent me from immediately frying the new board.
4) Are there other components other the the SLA7026M that normally are fried when these boards go out.

Thanks in advance,
Greg

[danhamm@abccom.bc.ca]

Greg are you sure you have your axis right?
My PR96 2000 model has pk296A SG3.6 2.2 ohm per
phase steppers on both X and Y axis, my Z axis
has pk268.02A 2.25 ohm stepper "which I want to
change to a larger stepper"..
as to your question about what would make your
transistor pop usually its,bad connection or a damaged wire,I blew mine by not having the plug in plugged in far enough and it blows the transistor and usually takes the resistor with it..

[Ted Hall, ShopBot]

Hi All,

I'll try to respond here in a way that makes sense with respect to each of the messages ...

First, so that others are not confused, this specific thread is about the drivers on older PR tools, not PRT tools.

What the drivers do on all tools is control the current to the motors ... trying to provide current at a constant value over the various operating speeds of the motor. They do this by the technique of PWM (pulse width modulation) also known as 'chopping' the current flow to the motors. To do it, they actually rapidly sense their own current flow, and then compensate accordingly by chopping the flow. Their primary area of vulnerability in this is that they will respond to a rapidly increasing resistance with increased flow and thus increased heating on their part. They -do- know when the motor is not plugged in and the circuit is open and do not respond; however, when a connection is going bad, such as with a loose connection or in the process of being unplugged, there is a good posibility that they will be sucked in, overheat, and fry. Indeed, you can usually feel damage on their surface when this type of failure happens.

The most likely causes that we have seen are: 1) the motor being disconnected while the power is on (you can get away with this at times, but try it slowly 10 times and you will have a blown driver); 2) a motor connector that is partially pulled out, at the control box or the motor and thus momentarily creating a high resistance connection (this is why we suggest putting a strain relief on the motor wires at the control box so that the wires cannot be inadvertently dislodged); 3) a bad connection at one of the wires inside the WAGO connector (e.g. too much or to little exposed wire); 4) a broken or cold solder connection in the high current circuitry on the driver board.

We have not had particularly good luck unsoldering and reworking these boards. It is hard to get the driver chip out without damaging the board (particularly without a re-work station). FYI, we socketed the drivers in the first round of boards for the PRT tools with the idea that it would make replacement easier. However, it had the opposite effect we intended because the socket itself makes the connection considerably more vulnerable to arcing and a weakening of the connection.

The driver on the PR tools, which is based on the SLA7026 has actually provided very good service and our failure rate has been quite low given the heavy service that these chips get (we have about 2000 of them in the world). We would have used it again, except that in the summer of 2000 there was 6 month delivery backlog and we could not get them (now there is little problem getting electronics components of any sort).

Current PRT tools use the latest generation of Allegro chips, which we are soldering into the boards. We have added transient voltage surpressors to reduce the vulnerability of the drivers, but it is too early to know how effective they are.

On Greg's situation, I doubt that the new motor had anything to do with it ... perhaps a wire or connector for the X axis got jarred in the process ??

And to Ed's initial question ... I am troubled that you keep losing the Y driver ... this suggest to me that there is a wiring problem somewhere between the driver and the motor or something else that is making this axis vulnerable. (Note too, you don't want to be manually pushing it around ...). Please give us a call to see if we can get this worked out and solve the $ problem.

[Greg Gressel]

Latest update which supports Ted's message:
1) This is an older ball screw drive Pr-32.
2) Latest discovery. About a month ago I upgraded the power supply to 24V. (This was wire in correctly to the power wires only.) However, when I was looking at the driver cards I did find a difference between the axis that blew and the others. The resistor on the blown x axis was 330 ohm while the other two were 470 ohm. Also for whatever reason the 330 ohm resistor has a socket while the other two are soldered into the board. I'm wondering if the resistor being 330 with the 24V PS was the root cause.
3) I appreciate your suggestion around the loose wiring. I didn't make a connection at the time but when I took the cover off the box the connector was partially off the board. (I had just moved the box around to access the motor that I replaced.) This may have been the final straw.
4) Should I use 470 ohm resistors. I have seen other notes on this forum regarding the possible use of a 680 ohm resistor. What are the pros and con to each?

Thanks for the help
Greg

[Ted Hall, ShopBot]

Ahh Greg ...

Have a look at the Technical Bulletins under 'Messages from ShopBot' here (there's one on adjusting drivers for 24 volts). Those resistors set the current to the motor, but they interact with voltage of the PS. We recommend the 680 for 24-28 volts. This will keep you at about 2 amps.