Series 2 BOSS 6 Axis motion problem

[craig96us]

I am considering replacing the control with gecko's etc, but in the meantime, I really need to get my Y axis running again so I can make some parts!

The failure occurred during a 20 minute or so period of time when the machine was sitting idle.

Specifics:
I pulled the front belt cover off to expose the position indicator drive, and allow me to see any leadscrew motion... If I try to jog the Y axis, the leadscrew shows slight motion in one direction, then motion stops while I can hear the stepper motor whine increase in frequency... When single stepped, the axis moves a step in the same direction each time. Positive, or negative direction motion is the same. Two sequential steps feel pretty solid, the next two feel weaker when moving in the - direction. In the + direction, all of the steps feel a bit weak.

There are no blown fuses...

Is this a common failure, and if so, what components should I be looking at? I have a maintenance manual, so I should be able to locate parts/testpoints etc.

TIA for any tips anyone can provide!

[craig96us]

A little more info:
I flipped the ACC board with no change, and swapped SMD with Z axis SMD, and no change...

[harolda]

replace 4 transistors on the transistor pack on the back door

[puller482]

I had the same problem the transistors will fix the problem. I keep an extra block of transistors as a backup. They seem to use these from time to time.

[craig96us]

Thanks!

I will replace the transistors and let everyone know what happens!

Actually my troubleshooting so far has lead me in this direction, so this tactic is right on track with what I am finding on my own!

This forum is a great resource, and I am grateful for the advice. Bridgeport information, and repair advice is getting quite scarce these days!

/Craig.

[puller482]

Craig here is a link to some files if you scroll down thru them you will find some info on changing those transistors. Be sure to use the heat sink compound when installing the block back on the heat sink.

Good Luck
http://metalworking.com/DropBox/_2000_retired_files/

[machintek]

It is also possible that one of the 12 diodes on the board beneath the ACC card is bad. When on of these goes, it does what you have described. By putting a meter on the base of the transistor, I notice that they do not turn on and off crisply. Instaed they turn off half way then finally off fully. By the way, the ACC is symetrical and by turning it around, you switch the X and Z current circuit but not the Y. In twenty years of BPT service I have only found one blown SMD board.
I cut and pated another answer in part below. Just substitute Y for Z.
Put the machine in jog, setup, z axis and step. Press the minus button repeatedly. Each time you do watch the small shaft and dial benath the Z axis motor. Made sure that it does not step in the same direction for three steps and then reverse direction for one. This would indicate a shorted final drive transistor (2N6547). There are 3 groups of these on black aliminum heat sinks above the ACC board.
It is also possible that your voltage in is wrong, you have a bad bridge rectifier, your current is set wrong, you have a chip or washer between two diodes on the small board beneath the ACC card, a chip or washer in the motor terminal strip beneath the ACC card, or the wrong transistors, or a high resistance in the Z axis DC fuse (screw in type, tan in color), or your quill needs to be cleaned with kerosene and use Mobil Vactra number 2 for way oil. I also once had a bad opto coupler on the ZDI to the SMD. Drove me crazy.
That gives you a bit to check.

[craig96us]

I will check the diodes as you described. I am at work right now, so I can't fiddle with the machine until later this evening.
I found the post that you pasted in yesterday evening while I was searching for more information that might help me fix this thing! After single stepping the axis, and not seeing the backstep, I decided that I should post my problem and see if anyone could help.
Your description in that post, and obvious knowledge of the inner workings of the stepper drive circuits is what prompted me to post my problem here! Thank you very much for being willing to help and share!
Based on what I read here, I now know that I may have a diode problem, and replacing the transistors could be an exercise in futility. I will have to determine if the diodes, or the transistors are at fault before I start shotgunning parts...

I will post what I find!

Just for fun, I am attaching a photo that my wife took of me working on interfacing my laptop with the BOSS6 so I could transfer gcode programs etc...

[craig96us]

Originally Posted by puller482 Craig here is a link to some files if you scroll down thru them you will find some info on changing those transistors. Be sure to use the heat sink compound when installing the block back on the heat sink. Good Luck http://metalworking.com/DropBox/_2000_retired_files/

I was able to locate files that appear to be related to diode replacement here, but I didn't see anything about the transistor replacement... Perhaps you can give me a filename? There are a LOT of files in that folder!
Thanks!
/Craig.

[craig96us]

The link that puller482 provided lead me right to the transistor plate! I found one of the power transistors to be shorted. I will be ordering + replacing. The transistor plate is a bit of a bugger to get to, easy to drop the screws etc.
Thanks a lot everyone! I will be making chips again soon!
/Craig.

[machintek]

How did the interface go? There are a LOT of posts about that in this forum also.
In another post I give a legthy description of how these drives work with voltage readings etc. If I find it I will post a link.

George W.

[craig96us]

Originally Posted by machintek How did the interface go? There are a LOT of posts about that in this forum also. In another post I give a legthy description of how these drives work with voltage readings etc. If I find it I will post a link. George W.

The interface took some time to figure out, but once I had the pinout information for the amphenol connector, I made up a serial cable with a DB9 on one end, and nothing on the other. I pushed the individual wires into the correct locations on the amphenol! My intention was to get it working first, and connect more permanently once it was working. The hardest part of the whole thing was figuring out how to transfer files, and break off the connection once the file had finished transferring... I ended up using hyperterminal at 2400 baud. At the BOSS6> prompt, Hit K <enter> to empty memory, and put the BOSS into "Input" mode. Next I would use the send text file function in hyperterminal to push the Gcode across. Once the transfer was complete, I had to hit CTRL+Z to get the BOSS out of terminal mode. It was frustrating to discover that there is no flow control on the BOSS RS232, so I ended up having to run the interface at 2400 baud. Any faster, and it would drop random characters. Usually the first character of the gcode block here and there. At 2400 it is almost rock solid. I added a delay of 15msec between lines, and presto! I am still pretty disappointed that the memory is so small. The BOSS6 will only hold about 600 some odd lines of Gcode. Once I have saved my pennies for a set of Gecko 201's or 210's, I plan to replace the BOSS. In the meantime I will have to live with it's limitations. I also have a 4 axis Shoptask that I built a few years ago. I can use it for the few jobs that require more than 600 lines of gcode if I have to. However I really don't have a lot of interest in running jobs on the Shoptask now that I have experienced the obvious advantages of the Bridgeport!

/Craig