MX-200 M DRO trouble

Just for fun

Just for fun

Tim Young
H-M Lifetime Diamond Member
Joined
Oct 7, 2020
Messages
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I'm having an issue with my DRO. The Z scale sometimes will not zero out. It will show some random number, on the MM scale it will sometimes shows between 24,000 and 60,000 mm.

I have my DRO setup so I can enter a coordinates. Sometimes and really most of the time it works like it should. I have swapped the Z and Y scales (cables on the back) and the trouble stays on the Z axis on the display. Here is a video of the problem, from the first DRO head. Has anyone else experienced this?

This is the second DRO to do this, I little different numbers but still the random numbers. Would it or could it be interference from the VFD causing this @mksj ? It only happens on the Z scale on the display no matter what actual scale I have connected to it. I have the power coming from the VFD cabinet but really has nothing to do with the VFD other than the power switch.

 
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Tim, try switching the Z and Y connections on the back of the DRO head unit and see if the symptom travels with the change. If you discover the Z is fine but now the Y has issues, then the problem is somewhere in the scale/encoder part of the DRO (improper gapping or interference). If the symptom doesn't move, and you still have trouble zeroing out the Z axis, then it's probably an issue with the head unit itself.
 
Yep, I have already did that and the trouble stays on the Z axis of the display. This is the second unit to do this, just different numbers but same problem. That's way I'm asking can there be something else causing this?

They will work fine for a while and once they start acting up if I power it down and back up it will work for quite awhile again.
 
You say you've tried a replacement unit and get the same problem? If so then the units must be defective from the factory
I guess the two options are try a third unit or get your money back
-M
 
Check the distance between the read head and the magnetic scale. My z axis readout started acting funny and displaying huge numbers when that got out of alignment. I called PM and they provided me with the right distance (16thou). They were a great help in troubleshooting this quickly.
 
I swapped the Z and Y cables on the back of the DRO and trouble stayed on the Z axis scale. I suppose they could both be out of alignment and only effect the Z axis of the read head.

Once it zeros it reads correctly as far as I tell.
 
The DRO does not need for the lathe or VFD to be powered up to work. Leave the lathe (VFD) turned off. Connect the DRO power to an outlet that has power and then move things by hand. Then you confirm that the VFD, or anything else associated with the lathe, is not producing any electrical interference. You can move the lathe axis by hand to observe the DRO.

Dave L.
 
Just for fun said:
They will work fine for a while and once they start acting up if I power it down and back up it will work for quite awhile again.
Click to expand...
One can conjecture all kinds of reasons....
WAG: In some older electronics designs they actually use internal batteries to hold the memory values and then these fail after time goes by. I have an old TEK oscilloscope (very expensive when new) that has a soldered in battery that provides power to the RAM which holds all of the calibration factors. It fails after a few years. It is a really bad design as this battery is buried deep internally and a great deal of disassembly to get to and then is difficult to unsolder and resolder without loosing the data. However, in the DRO case this would seem unlikely given the time frame of the design and the fact that it only happens on one axis.

WAG: There is a solder board connection that opens as the DRO warms up or is simply intermittent. I had a brake indicator light on my old truck that would stay on. The mechanic tried lots of things and then gave up. It was a bad solder joint in the dash circuit board. I pulled the board and just touched a bunch of connections with a hot iron to reflow the solder and it got well!

Good Luck.
Dave L.
 
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