richards
06-25-2009, 03:39 PM
Yesterday I had the first major problem since I bought my PRT-Alpha in July 2004. The piggy-back controller that plugs into the main controller board finally failed. Because I was running a huge file (almost 40,000 lines), I assumed that I had encountered a memory problem, so I upgraded from 1G to 2G of memory. No joy.
Next, I re-grounded the entire machine (error message related to no-data communications). Still no joy.
Finally, long after Shopbot had closed for the day, I called and left a message. Because I assumed that I would be on my own until this morning, I decided to remove the original piggy-back controller and install a V201. That fixed the data communications problem, by I only had movement on the Y-Axis. Meanwhile, Frank called and walked me through the possibilities. I didn't check the clock, but it must have been close to midnight at Shopbot headquarters.
At 4:00 a.m. I got up and connected my oscilloscope to the controller and started looking at signals. Pulses were going into the Allegro chip, but on two axes, no pulses were coming out. I still couldn't see the obvious problem. Because the Y-axis had Active High pulses and the other two axes had Active Low pulses, I decided that the problem was caused by the polarity of the signals and decided that it was time to graft in a logic chip (or two) to make the pulses all active low (to interface better with the Alpha stepper drivers) and to bypass the Allegro chip. Before cutting traces, I decided to call Frank one more time to verify that the pulse polarity was correct. He asked me whether I had tried running the X and Z axes from the A and B ports. That solution hadn't even crossed my mind. I soldered in the necessary connection so that I could move the X-axis and within a few minutes, all axes were moving.
Frank saved the day and from the tone of his voice, he did it with a smile.
Many thanks, Frank. I owe you one.
(By the way, the machine seems to run much smoother with the V201 controller card.)
Next, I re-grounded the entire machine (error message related to no-data communications). Still no joy.
Finally, long after Shopbot had closed for the day, I called and left a message. Because I assumed that I would be on my own until this morning, I decided to remove the original piggy-back controller and install a V201. That fixed the data communications problem, by I only had movement on the Y-Axis. Meanwhile, Frank called and walked me through the possibilities. I didn't check the clock, but it must have been close to midnight at Shopbot headquarters.
At 4:00 a.m. I got up and connected my oscilloscope to the controller and started looking at signals. Pulses were going into the Allegro chip, but on two axes, no pulses were coming out. I still couldn't see the obvious problem. Because the Y-axis had Active High pulses and the other two axes had Active Low pulses, I decided that the problem was caused by the polarity of the signals and decided that it was time to graft in a logic chip (or two) to make the pulses all active low (to interface better with the Alpha stepper drivers) and to bypass the Allegro chip. Before cutting traces, I decided to call Frank one more time to verify that the pulse polarity was correct. He asked me whether I had tried running the X and Z axes from the A and B ports. That solution hadn't even crossed my mind. I soldered in the necessary connection so that I could move the X-axis and within a few minutes, all axes were moving.
Frank saved the day and from the tone of his voice, he did it with a smile.
Many thanks, Frank. I owe you one.
(By the way, the machine seems to run much smoother with the V201 controller card.)