[justartingout]

I am currently enrolled in a Technical College for Machine Tool Technology. I am a workstudy for my shop instructor, and one of my duties as such is to see if I can fix machines when they break, but this ones got me stumped.

It was working fine one afternoon, but the next day when we tried to home, the Y motor moved faster than normal for a couple inches, then the Y DAC overflow error came on the screen.
I read the thread about EZ-TRAK SX not reading the hard drives, and it was mentioned that it may be the BMDC board. We have another EZ trak that requires an external keyboard to press f1 on startup, but it works fine after that, and this one was opted to be the donor. After unplugging both machines, I removed the BMDC from the probematic one, and replaced it with the donor, it then homed the Y, but gave me the same problem with the X. After putting the original BMDC into the donor macine, it also overflowed in the Y. Now, both BMDC's are in the original machines, and the first machine overflows in the Y, while the donor is back to normal.

Any help on this would be greatly appreciated, and if you need more clarification, let me know.

Thanks, Dan

[machintek]

A DAC overflow means the control asked the axis to move and did not see a response. In other worked you have a bad position loop. This usually means a bad encoder. But it could also be a bad cable or a bad connection somewhere and/or a bad BMDC (but you eliminated this).
FYI: A encoder can be good and count but a machine can still not home if the marker pulse has stopped working in the encoder. The machine looks for the switch and then the marker pulse. If you start the homing process with the machine on the home switch, it will back off and come back on the switch. If it never reverses direction after coming off the switch, the switch or wiring is defective.
If an encoder shorts out or a cable shorts out on a pre-cutler hammer control machine, it will fry the L1 on the BMDC. Starting with the cutler hammer control, there is a circuit breaker on the 5VDC so this should not happen.
If you know how to get to DOS, with a full size keyboard, go to the root directory, type in PFM.exe and return (enter), cursor down to tuner, hit enter again, and you will be in a tech screen that is very helpful in diagnosing problems.
The other machine needs the CMOS battery replaced. It it has the half size mother board, it may have a Dallas Real Time Clock chip instead. That also can be replaced. Google it.

George

[DGeoLab]

Hi to all,
We had the same problem here. I found that the lamp in the encoder
had burned out. When I replace the bulb - that problem went away.

Now unfortunately I get and error when trying to home that "power on failed"

Any Ideas?
THanks,
David

[NC Cams]

Must be contageous. Check this out for more info with identical problem:

http://www.cnczone.com/forums/showthread.php?t=20721

[Al_The_Man]

I found that the lamp in the encoder
had burned out.

Holy Cr*p, how old are those encoders?
I haven't heard of lamps in encoders since the Ferraniti-Packard days.
Al.

[NC Cams]

BTW, the machine that you have to push the F1 on may have a CMOS battery going bad.

It may also have a HDD/FDD card going south. IF the HDD/FDD goes bad, the M/B can get hurt as well - happened to ours.

If you lose the M/B, you're in for a ration of grief that is frustrating and potentially expensive... Been there, done that...

[hotrob1]

I've heard of people replacing the motherboard and resolving the "DAC overflow" problem. Is this common?

-Hotrob1-

[machintek]

DAC overflow is a condition where the control calls for movement of an axis and does not see it move.
NOT mother board related.

George

[hdjeffrey]

coming back from christmas vacation ,fired up lathe and z dac overflow! read in some threads to swap servo motors and see if the problem followed the motors, it did not! then swaped out limit switches ,still the same , i guess its a process of ruling things out !

[NC Cams]

Read between the lines in post number 8 - limit switches have nothing to do with encoder outputs.

BIgger hint - check encoder output with an oscilloscope.

BIGGER HINT YET. make sure the encoder cables pin out from servo back to AXISBOB card.

IF you do encoder check with scope at AXISBOB, you do all checks at once.

If encoder input is going to the BMDC, that could mean BMDC service is needed. ONly EMI does that.and it is somewhat costly.

If you eliminate problems by swapping out the wrong stuff, you may not get results anytime soon. Swapping of servo motors does nothing to validate cables or internal wiring issues - repeated cable flexing and /or oil soaked cables does nothing for their durability over time. Even externally "pristine" wiring that has had the hell flexed out of it may not still be conducting properly. Better yet DO A FULL PINOUT OF THE CABLE UP TO THE AXISBOB ribbon connector into the BMDC.

ALl this pinout crap takes a while but you can figure it out.

[Dagon]

had the same problem, wasn't the encoder or motor, cables ect.. finally swapped out the x and y drives, and the problem followed the drive.. according to Hardinge, you can swap x and y, but not the z drive for troubleshooting. Once the problem is found, you should return them to original positions as they are tuned for that axis..
Anyway, went to hardinge and after a bit of a search, found and purchased a new drive amp and all is well.
Hope this helped.

[NC Cams]

As I recall, any error that is associated with the amp can come back to the BMDC via one singled OR'd signal from any of the amps via the one error path. THis is usually thru wire 28 fed to pin JP 10-1 on the AUXBOB card. Check your schematic for detials.

THis means that ANY amp error, be it over volt, over current, move asked for/not made that occurs due to an amp fault of ANY kind will be displayed as DAC overflow. In light of the easy of changing/swapping amps, I"d be inclined to swap amps first with ohter stuff to go thru the musical chairs routine thereafter.

[machintek]

A axis drive fault creates a axis drive fault. But if the motor does not turn, you get the DAC overflow. A dead drive can create a drive fault. The absence of a axis ready signal can create a axis drive fault.
I was just called in to a TC-22 with a unspecific drive fault. Actually 2 of them about 3 hours from each other. Turner supply, the BPT dealer here in Alabama told one customer that all 3 axis drives were bad. Customer called me in. I found only a bad spindle drive (yaskawa) which came up as a drive fault. I found this by isolating the fault lines.

George

[NC Cams]

Servo amp repair hint.

For some reason, the optoislators can take a dump on the MSI driveas - Look down on the component side of the drive and the left corner opposite the drive fets iw where they are located - 2N37 as I recall is what they are/were.

For a couple bucks you can find some that are much more robust and solder in your own. Did that on mine and put them in gold plated IC sockets. This hour long fix with about 5 dollars worth of parts can save you HUNDREDS in repairs - that's all a noted refurbisher of MSI amps does to "refurb" them. OVer amp and under votage are sent out as an OR"d signale from each amp, the amp signals are then OR"d into the BMDC.

THe "or'ing" of the signals is why you need to separate the fault line from the BMDC - if you just check the line, you'll falsely think that all three amps are bad. ANd to think some guys just might fall for that line.

[hotrob1]

The previous error was a faulty drive. Since they remove the info from the chips I had to purschase new drive.

Second problem turned out to be faulty contactor with neither drive getting any input voltage. Simple fix, but working now.

Hotrob1

[MechanicalJim]

We ran into this problem on our BP EZ Trak just the other day so I pulled the Y feed motor off along with the belt and the pulleys and found the two precision thrust bearings at the front of the shaft were completely destroyed... So I ordered new ones and I'm gonna see if it solves the problem...

[pathwizard]

I know this thread is quite old, but I'm struggling with similar problems.
Noted above about 5V short "will fry the L1 on the BMDC", how do I know if my machine has a circuit breaker. If it does, where is it and how do I reset it? My machine is year 2000 Series 1, V2XT. I did briefly short the 5V line and it now reads 0.6V.
Thanks for any help.