Mitotoyo Absolute Solar Caliper Malfunction

[macalla]

I have a Mitotoyo Absolute Digimatic Solar Caliper model 500-475, maybe 10 years old.

It suddenly started mis-measuring in a pretty random way.  It's a 8" caliper, but opening it up all the way measures just over 6" It seems to return to 0 reliably though.

I don't see any debris in the tracks and I cleaned the exterior with alcohol already which didn't help.

One thing worth mentioning is that the front glass popped off recently for no good reason. Right now I just have it taped down till I have time to reglue it. This was a few weeks ago and it's been working fine until yesterday.

Anyone have ideas?

[sean0118]

My first thought was maybe the internal battery was going bad and swelling up, which could explain why the cover fell off too. Except looking at photos online it seems it has a really small coin cell or maybe a super cap, so that's probably not the issue.

What sort of sensor do these use? Is it optical?

[amyk]

Does it read everything as 0.75 what it should be (which would be highly unusual), or does it seem more like it's skipping counts at certain portions of the scale?

[macalla]

It does seem to skip counts at distinct points on the scale, I've also seen it flip from a positive number to negative number, possibly at the same points.

Don't really know what the kind of sensor it uses.

[macalla]

just checked it again; it doesn't skip so much as go backwards at certain points.  Also noticed that E shows up as the last digit sometimes

I'm guessing this measures the resistance of the black strip under the sensor?

[jpanhalt]

Re: sensor

I had thought they were capacitive, but the Mitutoyo manuals seem unclear:  https://www.mitutoyo.com/wp-content/uploads/2015/08/D-Section-US-1003-Calipers.pdf

Both attachments are for "500 series."  The first says, "capacitance;" the second says, "electromagnetic induction."  It may depend on a specific part number.

BTW: I have had my Mitutoyo 6" digital caliper for a long time (> 20 years) and have never had a problem like you describe.  Mine is just battery powered.

[macalla]

ahh, thanks. The first one is for the solar type that I have.

[floobydust]

24 years ago... QA guy at work binned a Mitoyo 500 6" because the jaws were apparently worn a few thou from measuring pipe diameters. Yup I scooped it up because the tips were still accurate and fine for PCB work 

So... the other day I spilt iced tea on it (and the PC keyboard) and had to take them totally apart.

There are youtube videos, but basically unscrew the battery compartment, top two hex setscrews for the tension bar, and the four screws on the backside, three were under the label so I used a razor blade to pry up a corner to expose each screw without removing the entire label.
Inside used IPA and q-tip to clean the sensor array, slide, keypad. I did not pull out the LCD.
If the tension bar is set loose, the head wobbles, it can also give jumpy numbers. Or if the PCB sensor (it looked capacitive quadrature) array is dirty readings will jump around.

They still work great.

[YetAnotherTechie]

Error and skipping is a sign of low battery, open it, clean, replace the battery. Don´t pull the sticker from the main scale.

[macalla]

well i took it apart, cleaned everything, reassembled.

problem gone.