Author Topic: Fixing my digital DRO scale -- and a caliper, too  (Read 2358 times)

Offline vtsteam

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Fixing my digital DRO scale -- and a caliper, too
« on: April 05, 2013, 07:56:33 PM »

About 5 years ago I bought 3 DRO scales intending to put them on an Atlas horizontal mill, but never got around to it. There were two 6" scales and one 12".  Yesterday I pulled them out of their boxes and was considering adding one or more to my newer mill drill, and maybe one to the lathe.  :dremel:

But after storage for several years, the longer scale had a problem -- one of the segments on the "inches" digit was always on (black). This made 5" and 6" indistinguishable, as well as 8" and 9". Other numbers were pretty good, but the confusion of these two sets would probably prove disastrous on the mill. Naturally it was the longest scale, and a replacement would now cost $100.  :bang:

I opened up the case and looked at the PC board (one IC only) and removing and replacing the LCD, and replacing the battery, nothing had changed. On another forum someone suggested cleaning the LCD contact and glass. I wasn't sure what this meant since the connector seemed attached to the LCD (the black strip on the back of the LCD in the photo above).

After fiddling around with it with a Q-Tip and alcohol, I noticed part of the connector appeared loose. Trying to carefully replace it with tweezers caused it to come off altogether.  :hammer:  Then I realized it was just a rubber conductive strip and not supposed to be attached to the glass at all. Phew! I took it off and cleaned it. Remembering to replace it with the little grooves up (barely visible in the photo above).

There were also some barely visible conductive coating lands under it on the glass. So that's what was meant by cleaning the glass! Sorry to say, cleaning with alcohol and attempting to shift the LCD connector slightly (also a suggestion) didnít fix the read-out ó so the general conclusion was that probably the driving IC was defective.

Thinking about it for awhile, I wondered if I could replace the circuit board with one from a cheap 6" caliper -- since the digital bodies looked almost identical. It so happened that I had a defunct caliper whose display had gone blank about a year ago. I wondered if the problem in that caliper couldn't be cured by cleaning its LCD and connector -- the way I'd done the DRO scale.

So, I took it apart, and simply removed the PCB (which looked almost identical to the one in the DRO) and plopped it into the DRO body). The glass contacts and LCD were already clean in that one.

SUCCESS!!!!  :ddb:  The DRO functioned normally.  Wooooohoooo!!

Well in for a penny in for a pound -- Fingers crossed.  I tried cleaning the glass and connector on the remaining 6" caliper body, and put the DRO's PCB into that one. Unfortunately the same segment as before was black. HOWEVER, it wasn't such a big problem in the caliper, because only 5" and 6" could be confused, and the only time it would be 6" is when the caliper was fully open -- any other time would be 5" or less -- so pretty obvious.  :ddb:

Now I have two repaired tools! And I think I might be able to turn off the remaining LCD segment in the caliper -- since it isn't needed, if I put tape over one of the contacts to the LCD that controls it.

It wouldn't work if the segments are multiplexed. Not sure about that. But if I can't do it that way, I can always put a dot of silver grey paint on the glass over the  offending segment to hide it. The bigger hammer method.  :wack:

Anyway, Just thought I'd pass this on in case someone else has a problem with a digital caliper or similar DRO scale. Get down to that rubber connector on the LCD and give it and the glass under a careful cleaning with rubbing alcohol. I bet many defunct calipers can be resurrected this way!
I love it when a Plan B comes together!