Boss 5 Y axis problem?

[jeaBOSS5]

I have a Boss 5 machine that the Y axis started giving me problems today. In the middle of a G79 command during a dry run (not cutting metal) it crapped out. It will step in .001 steps, but in .010 steps is stalls. I checked the usual suspects: transistors are good, swapped the SMD boards around and still have Y axis problems. Any suggestions as to what to try next..some one told me to try putting the ACC board in upside down.. can I do this if so what will that do? Any help or suggestions is much appreciated.

John

[machintek]

The upside down ACC board swaps the X and Z parts of the board. The Y is still the same. Check the voltage at the fuse. You may have an open leg on the bridge rectifier. Do you have plug in fuses or screw in? The screw in have a tendency to develop a high resistance and cause problems. Have you checked the current at the fuse? Bad ACC or bridge rectifier. Chips or screws or washers falling down between the diodes on the board beneath the SMD or onto the terminal strip to the motors will also cause a problems such as yours.
Start with the above.

George

[jeaBOSS5]

George,

Thanks for the information and direction. I have Plug in fuses, I will check the voltage and current. How can I check the bridge rectifier? Where is the bridge rectifier located? Is there any particular component(s) on the ACC board that I could test?

John

[machintek]

If you look behind the electrical cabinet that the logic boards are in, you will see a heat sink sticking out. The brige rectifiers are in that heatsink. The white capacitor cabinet just below the tape reader is pulled out (not fully) and the heat sink is unscrewed from the back of that. Check the wiring schematic. The bridge can be checked by isolating it and using diode check or ohms on your DMM.

George

[jeaBOSS5]

George,

Thanks,
I have tested the Bridge Rectifier and it was bad. I replaced it and the machine seems to be running fine. But, I decided to check all my voltages and currents per the maintenance manual while I had everthing open just to make sure there was not anything else wrong that may have caused the blown Bridge. My line voltages are good, Input and Output to T1 are good, Input to T2 good output of T2 I have 55 volts between one set of 5,6 terminals, other two sets are good. I did notice other taps (7's and 8's) that I measure 58 volts between 5 and one of these, can I switch to one of these taps to correct the one set that is at 55 volts? 24Vdc terms 40,39 checked at 23.6, 56 vdc terms 74,76 checked at 54.6, terms 75,39 checked at 54.5.
X axis current 8.43 amps static 4.3 moving, Y axis 8.7 amps static 4.6 moving.
X axis Voltage Stable at 6.5 vdc after clearing limit switch goes to 8.4
Y axis Voltage Stable at 6.7 vdc after clearing limit switch goes to 8.6
According to the maintenance manual these should be 38 - 42 vdc is that correct? If so what could be causing this undervoltage? The machine seems to be running correctly. Will I cause any damage by running it like this?

Thanks Again,
John

[machintek]

I have never seen current values that high in a rapid move. Typically they drop to about just above 2 amps. At 4 amps, the motor magnetic fields are so weak that I would have to turn the rapid rate down on the RCK/ZCK to keep it running. The other possibility is that because your voltage is so low, the motors do not get to their max speed, hence current is high. What is AC volts into the machine?
You can more the wires on the number 6 tap up to get a higher voltage getting better performance. Do not exceed 63 VAC.
Yes, in theory when the drives are off, your voltage should go up on the DC fuses. Do you have the small SMS board?

George

[EDM_Fixer]

could be brush dust if this is a dc ..also clean your encoder ... dont leave a film from the alcohol, polish w/dry clean q-tip... either one or both can add in to what i'm hearin ...

[machintek]

Good advice but a BOSS 5 has stepping motors and no brushes. Worse yet it has an open position loop. There are no encoders. This was to save money way back then and since it had steppers, the control, in theory, could still tell an axis how far to move.

George

[fredhh47]

I have experienced similar problems on Boss 5 and 6 machines. The voltage readings may be caused by improper set up of the three phase wiring. The "wild" leg of the three phase should not be connected to the power supplies, but should only come into play when the 3-phase motor is started and the voltage on that leg is not critical. On my system, I can get anywhere from 180 to about 260 on the wild leg. I think my electrician warned that the wild leg should be connected to the main fuse that is closest to the side of the cabinet, but you can check your schematics to see where the power for your power supply module comes from. Also, I have had good readings from transistors that failed moments later. I use ECG53 or equivalents in all three axes.