Acu-Rite III scale disassembly help needed

Y-axis scale isn't working on my newly acquired mill. Only 1 set of pulses
is getting to the box (white wire, top). Cable checked OK and wiring at
connection to scale checked OK. Only thing left is inside the scale.
The scale worked intermittently when I checked it out so I was hoping for an
easily found bad wire, but no luck.
Any advise or precautions before I remove the scale from the mill and open
it up?
BTW, the Acu-Rite III box wasn't working when I got it. Not dead, just no
good readouts, and sometimes it would take a preset, sometimes not. I
opened it up and found a dual voltage power supply, 5 v and 13.8 v. An
18000 uf 15 VDC cap keeps it going (20 yrs old) .
The 13.8 v is dropped to 10 v across a zener diode. All was well until the
display was lit when I did a zero reset. Then the zener dropped to 8.4 v.
Pulled the 13.8 v pin from the cap to the board and hooked up a 12 v supply
to the board. Steady 10 v at the diode and all worked well. Ordered a new
cap for $10 from mouser.com.
Any help is appreciated.
Regards,
David
Reply to
david
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I don't know which scales are used with the Acurite III, but I've been inside a few of the ENC150 scales for my Acurite MillMate and TurnMate DROs. Just use a little common sense and don't force anything--there's nothing mysterious or particularly fragile. On my scales the read head slips out the end after removing the end cap. There's a cute 5 degree-of-freedom linkage between the junction box and the sensor which allows the sensor to align itself to the glass scale. The seals will usually slide right out of the extrusion.
You may be shocked at how much crud is packed into the scales. Wipe or brush out the bulk of it, and clean the glass scale with paper towel and alcohol, doing your best not to drag chips over the scale. They're surprisingly tolerant of damage, but no point in pushing your luck.
I clean the reader heads by spraying with plastic-safe contact cleaner.
I did resplice one reader head to its cable on a scale I bought for $10. The tiny teflon wires from the sensor are a bugger to strip. A microscope is big help.
Acurite has downloadable manuals for many of their scales online. Check that the scale and reader head are properly aligned per the manual.
Ned Simmons
Reply to
Ned Simmons

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