Need Help! Bridgeport Series 1 Boss 6- Need help troubleshooting factory stepper drive system


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Thread: Bridgeport Series 1 Boss 6- Need help troubleshooting factory stepper drive system

  1. #1
    Activation process codymnelson's Avatar
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    Default Bridgeport Series 1 Boss 6- Need help troubleshooting factory stepper drive system

    Hello all,
    I have been reading on this site to try to get my Bridgeport Series 1 CNC back up and running, but I haven't been able to fix it yet.
    I was making a cut in the X axis when the table stopped moving. The control display still showed movement because it still thought the table was moving.
    I hit hold and restart on the control to cancel the rest of the move and then i retracted my Z- axis to get the cutter off the work.

    I ended up shutting the machine down after finding that I had lost both the X and Y axis motion.
    I found that the machine had blown fuses 12 and 13 which are the DC fuses for the stepper motors for X and Y axis respectively. I made a test lead and used my amp clamp to see what kind of failure i had. I have a 16 amp draw on X and a 13 amp draw on Y at about 30 volts. I only had those under power for a short time to find this out, and then powered it back down. Fuse 14 for the Z axis never blew, and its current when stationary measured 8 amps at 9 volts DC. I never left the jumper in long enough to try moving them. I did notice that they locked up as would be expected under power. The windings on all three steppers have similar ohm measurements and I cant find anything that tests as a short.

    I read and researched my problems here and ended up replacing all the power transistors on the back (side) door for both X and Y axis. There were 4 on each of the black aluminum rails. I un soldered, cleaned up and replaced the transistors and diodes and reinstalled them into my machine. I also had moved these around as a test prior to replacing them, and never saw a change in which axis had problems or worked, but I still changed them out since it seemed like the classic failure on this machine.

    I powered up the machine and found no change in behavior. I could not find any other glaring faults or places where the smoke got let out. I have 63V AC coming off T2 to each of the 3 axis bridge rectifier/reactor circuits. The AC fuses that are between the reactors and the bridge rectifiers are good. I have 24VDC control power at fuse 6, and I have 56VDC power on fuse 10 as well as at the reactors. I tried hooking up my X axis stepper to my Z circuit and it worked correctly and drew the correct 8 amps while stationary. I took that to mean my X stepper did not have a short in it and reconnected it back to the original drive circuit. I tried moving around the SMD boards and flipping the ACC board, but nothing would move the problem around. Z always works while x and y never do. I always powered the machine down to change and move components and pull/insert fuses as I have been doing these tests. I also compared voltage between wires 24,26 and 28 coming out of the bridge rectifiers, and with no fuse installed, all three axis were the same voltage at 84 volts. I never saw this high of voltage with a fuse installed. I guess you would call that the open circuit voltage, but regardless, it was consistent between the working and non working axis. I saw no AC power on wire 24, 26 or 28, just DC, so I think the bridge rectifiers are healthy.

    I went thru my maintenance manual and schematics and tried to understand how this system works. I now understand that the ACC control card inside the control cabinet outputs power to run a saturated core reactor for each axis. This is to reduce the current draw at stop by the stepper motors. In talking it thru with my neighbor who is an electrical engineer, he suggested looking at these outputs to the reactors with an oscilloscope.
    He lent me a scope, and I looked at terminals 17,18 and 19 for the ACC output to the saturated core reactors. Thru out this whole process my Z axis stayed functional, so I looked at it first on wire 19 and saw a waveform matching what the maintenance manual shows as expected. This made sense since it was working correctly and was only pulling 8 amps while stationary.

    I shut down, added my amperage test setup to X and then Y, and looked for a similar signal on wires 17 and 18, but found noting of the sort, just a small constant DC current. This means the ACC board is not doing its part to reduce current draw.
    I then looked at the ACC board and tested everything to the best of my knowledge. The transistors on the board were all dated from 1978, so I ended up replacing all 9 of the large transistors and all 15 of the smaller ones as well all on the ACC board.
    I tested circuits on that board and attempted to compare the readings i got on different segments of it trying to find any differences between x,y, and z circuits. I adjusted the voltage pots on the ACC board for x and y to the same value as Z was set to and got identical readings on voltage drop, resistance, and capacitance throughout the board.

    I reinstalled everything just now and I still have no change in behavior from my original failure. Z works, but X and Y draw too much current. I confirmed with the scope that the ACC board is still not outputting a signal to the reactors to cut the AC current to the bridge rectifiers. That is still my problem, but I don't know what else to look at to try to fix it.
    I feel like i need to confirm that the ACC board is getting all the inputs it needs to function, but i haven't figured out what they are yet. It looks like it gets a signal from each SMD board. I think the ACC card header pin numbers are 5-7 for X, 6-40 for Y, and 39-38 for Z. I don't know what to expect to see, but I will try to compare the good axis to the bad and go from there.

    I know this is a ridiculously long post, and I apologize for that. I am trying to share all the details of what i have done, but I fear i am still leaving out things i have tested.

    I could really use some help from anybody who remembers these old machines. I am running out of ideas, and I need to get it running to complete a job that I took on with it.
    I appreciate any suggestions or ideas. Heck, I even appreciate anybody who reads this whole post.
    Thanks! Cody

    Machine details-
    Labeled on upper frame as a Series 1 CNC. S/N inside the power cabinet is 7066. It weighs 5500 lbs and has the larger knee and table of a Series 2.
    I have a 2:1 ratio on the stepper motor pulleys versus 1:1, and i have a ZDI board instead of an XDI, which both make me think it is a Boss 6 versus 5.
    I do not have a drum switch for the spindle, it has the electric motor fwd/reverse contactor.
    It has the pneumatic speed control and brake actuator.

    Similar Threads:
    Cody Nelson


  2. #2
    QPOWIER's Avatar
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    Quote Originally Posted by codymnelson View Post
    Hello all,
    I have been reading on this site to try to get my Bridgeport Series 1 CNC back up and running, but I haven't been able to fix it yet.
    I was making a cut in the X axis when the table stopped moving. The control display still showed movement because it still thought the table was moving.
    I hit hold and restart on the control to cancel the rest of the move and then i retracted my Z- axis to get the cutter off the work.

    I ended up shutting the machine down after finding that I had lost both the X and Y axis motion.
    I found that the machine had blown fuses 12 and 13 which are the DC fuses for the stepper motors for X and Y axis respectively. I made a test lead and used my amp clamp to see what kind of failure i had. I have a 16 amp draw on X and a 13 amp draw on Y at about 30 volts. I only had those under power for a short time to find this out, and then powered it back down. Fuse 14 for the Z axis never blew, and its current when stationary measured 8 amps at 9 volts DC. I never left the jumper in long enough to try moving them. I did notice that they locked up as would be expected under power. The windings on all three steppers have similar ohm measurements and I cant find anything that tests as a short.

    I read and researched my problems here and ended up replacing all the power transistors on the back (side) door for both X and Y axis. There were 4 on each of the black aluminum rails. I un soldered, cleaned up and replaced the transistors and diodes and reinstalled them into my machine. I also had moved these around as a test prior to replacing them, and never saw a change in which axis had problems or worked, but I still changed them out since it seemed like the classic failure on this machine.

    I powered up the machine and found no change in behavior. I could not find any other glaring faults or places where the smoke got let out. I have 63V AC coming off T2 to each of the 3 axis bridge rectifier/reactor circuits. The AC fuses that are between the reactors and the bridge rectifiers are good. I have 24VDC control power at fuse 6, and I have 56VDC power on fuse 10 as well as at the reactors. I tried hooking up my X axis stepper to my Z circuit and it worked correctly and drew the correct 8 amps while stationary. I took that to mean my X stepper did not have a short in it and reconnected it back to the original drive circuit. I tried moving around the SMD boards and flipping the ACC board, but nothing would move the problem around. Z always works while x and y never do. I always powered the machine down to change and move components and pull/insert fuses as I have been doing these tests. I also compared voltage between wires 24,26 and 28 coming out of the bridge rectifiers, and with no fuse installed, all three axis were the same voltage at 84 volts. I never saw this high of voltage with a fuse installed. I guess you would call that the open circuit voltage, but regardless, it was consistent between the working and non working axis. I saw no AC power on wire 24, 26 or 28, just DC, so I think the bridge rectifiers are healthy.

    I went thru my maintenance manual and schematics and tried to understand how this system works. I now understand that the ACC control card inside the control cabinet outputs power to run a saturated core reactor for each axis. This is to reduce the current draw at stop by the stepper motors. In talking it thru with my neighbor who is an electrical engineer, he suggested looking at these outputs to the reactors with an oscilloscope.
    He lent me a scope, and I looked at terminals 17,18 and 19 for the ACC output to the saturated core reactors. Thru out this whole process my Z axis stayed functional, so I looked at it first on wire 19 and saw a waveform matching what the maintenance manual shows as expected. This made sense since it was working correctly and was only pulling 8 amps while stationary.

    I shut down, added my amperage test setup to X and then Y, and looked for a similar signal on wires 17 and 18, but found noting of the sort, just a small constant DC current. This means the ACC board is not doing its part to reduce current draw.
    I then looked at the ACC board and tested everything to the best of my knowledge. The transistors on the board were all dated from 1978, so I ended up replacing all 9 of the large transistors and all 15 of the smaller ones as well all on the ACC board.
    I tested circuits on that board and attempted to compare the readings i got on different segments of it trying to find any differences between x,y, and z circuits. I adjusted the voltage pots on the ACC board for x and y to the same value as Z was set to and got identical readings on voltage drop, resistance, and capacitance throughout the board.

    I reinstalled everything just now and I still have no change in behavior from my original failure. Z works, but X and Y draw too much current. I confirmed with the scope that the ACC board is still not outputting a signal to the reactors to cut the AC current to the bridge rectifiers. That is still my problem, but I don't know what else to look at to try to fix it.
    I feel like i need to confirm that the ACC board is getting all the inputs it needs to function, but i haven't figured out what they are yet. It looks like it gets a signal from each SMD board. I think the ACC card header pin numbers are 5-7 for X, 6-40 for Y, and 39-38 for Z. I don't know what to expect to see, but I will try to compare the good axis to the bad and go from there.

    I know this is a ridiculously long post, and I apologize for that. I am trying to share all the details of what i have done, but I fear i am still leaving out things i have tested.

    I could really use some help from anybody who remembers these old machines. I am running out of ideas, and I need to get it running to complete a job that I took on with it.
    I appreciate any suggestions or ideas. Heck, I even appreciate anybody who reads this whole post.
    Thanks! Cody

    Machine details-
    Labeled on upper frame as a Series 1 CNC. S/N inside the power cabinet is 7066. It weighs 5500 lbs and has the larger knee and table of a Series 2.
    I have a 2:1 ratio on the stepper motor pulleys versus 1:1, and i have a ZDI board instead of an XDI, which both make me think it is a Boss 6 versus 5.
    I do not have a drum switch for the spindle, it has the electric motor fwd/reverse contactor.
    It has the pneumatic speed control and brake actuator.
    Hi Cody, I read throught your description about the process of failure. I guess perhapse something blocked your table while it was moving along X direction.And then overcurrent occured. The fatal disadvantage of the stepper motor system is the open loop control mode. You'd better lead to close loop in the future. No matter what the close-loop stepper motor or servo motor would be OK. Servo would be better.

    I could try my best to help you with your problem. Could you provide some technical files, such as the CNC's specificaion(nameplate), operation manual, electrical schematics and so on?
    What's more. I need the PCB pictures of your controller.

    If the files are too large to post, you may send them to my email:
    oossppp@outlook.com
    Thank you



  3. #3
    Member mactec54's Avatar
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    Default Re: Bridgeport Series 1 Boss 6- Need help troubleshooting factory stepper drive syste

    Yes the Boss 6 are 2:1 Boss 5 are 1:1, It may have a different name other than Boss, most of the parts are the same though, this is common to get the problem you are having, most throw out the old junk and add a new control, you have done everything that normally fails, which leaves board level problems and unless you can find some cheap Boards trying to fix them is almost imposable as most of the parts are obsolete

    The Bridge Rectifier would be worth a look at , and the SMD Board may have a problem

    Mactec54


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    Default Re: Bridgeport Series 1 Boss 6- Need help troubleshooting factory stepper drive syste

    I made some progress in getting this machine working. More accurately, my neighbor made a discovery that gave me a direction to pursue. When I originally got this machine I was able to run it on native 3 phase for several years in the warehouse of my day job employer. It was a high delta, but still, it was 3 phase and it worked well. I ended up losing that job perk when i transferred. I brought it home and worked on getting it powered on single phase. I added a VFD for the spindle motor, which was the easy part. My machine has a 3 phase transformer. It has three sets of windings that all share a common core. I thought I had figured out a way to wire it to get 63v out of 2 of the three sets of windings. In fact, it worked that way for several months. I had coupled the x axis with the y axis and fed them both from one transformer. Again, it worked for a while, but it ended up being my undoing. Seeing what that transformer output looked like on my neighbors oscilloscope was enough to know that things weren't happy. While my meter showed a 63V AC output, the scope showed that the waveform as all messed up and not sinusoidal. Once we removed one of the axis, the waveform cleaned up. It seems like the two saturated core reactors were both trying to magnetically couple to the transformer, and it wasn't good.
    I ended up ordering a 2 KVA stepdown transformer and wired it up to the z axis so i can keep all three separated. I seem to be back up and running at this point. I am at least back to where I was. I still have to figure out why i was having trouble with rapids in the y axis. That was happening before the failure, and it still persists thru this episode. Based on what I read here, I need to verify that I dont have a mechanical binding issue first and go from there.

    I want to say thank you to all of you for the vast amount of information you have accumulated here on this site. It is greatly appreciated.

    Cody Nelson


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