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DTI Challenge 2022

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I've had this DTI sitting in a drawer for easily 5 years. I got it at a flea market. Hard to read even what the dial says under the yellowed glass, Federal and then Model C21, and .0001".

From the overall condition, long storage and, now I see, missing screws, I'm worried the insides aren't in great shape....

Guess I'm going to try taking it apart. Maybe Bob is watching ....... I hope!  :borg:

Three screws held the bezel on. I didn't want to bend the hands by lifting it straight off, because the numbers ring would have interfered. But I was able to lift it at the short end of the pointer, then shift the whole bezel up and off the hand, and free of the body.

I removed the large pointer by slipping a pair of tweezers under it, closing them lightly, then lifting up so that each arm of the tweezers was lifting flat against it. It came loose with a little pressure, and I was glad the hand wasn't bent in the process.

The small hand was a little more difficult to figure out. I couldn't fit the tweezers under it. But two miniature flat bladed screwdrivers did fit under, and luckily, it was an easy sliding fit on its shaft.

I then took off the zero adjust cap at the top of the gauge, and removed the back of the DTI. There were only 2 screws of 4 in the back. The mechanism cage is brass, but the instrument case itself seems to be zinc die-cast.

The works looked better than I had feared. But the screw holding the brass plate on in the upper left corner was corroded some. It is located where the two missing screws in the outer case rim were. you can just see one of the resulting holes in the case, above it.

I was able to turn the other three screws without a problem. But I couldn't budge the corroded screw. I haven't applied too much force, as I don't want to strip the slot or twist off the screw. Not sure what to do here exactly. Maybe some kerosene (paraffin, UK) applied with a toothpick on the screw post joint under the brass plate....?

The movement seems to be pretty good, and from what I can see, undamaged. But it is slightly noisy -- and occasionally tends to not return to zero perfectly without a little help, so I think it needs cleaning.

I am a little nervous about opening it up further. I have visions of parts springing out all over the place, and/or not being able to replace everything exactly where it goes, and in proper relation/orientation.

I might give it a pause here, in case Bob chimes in.......... :scratch:

Were it me, at this point Id pop it in my ultrasonic cleaner to dislodge any gunge then rinse in distilled water or IPA and gently blow dry. With any luck it will also loosen the stuck screw.

Im assuming at this point the dial with its printed overlay is off as that should not go in the tank.

(My ultrasonic cleaner these days mostly gets used for cleaning my glasses on which it does a splendid job!)


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