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Restoring Circuit Diagrams and Schematics

by Ken Bushell

Many times, when restoring telephones, the circuit label inside the phone will be found to be damaged, discoloured, marked or faded as per the illustration. These can be replaced by photocopying the original and repairing any damage as follows:

(1) For a dirty and damaged diagram, copy the label with a photocopy set to light, then copy the copy again but make sure to turn it 90o in the machine (this is to keep the image square as most machines do not copy square).

(2) Now copy the second copy (still in light) but set the machine to enlarge (double size is A4-A3, A5-A4, or 141%). Now copy again turning the image around again.

(3) Carefully white out any marks, etc., from this copy using liquid paper or similar (I usually thin liquid paper so that it does not build up too high). If there are large areas between lines which are dirty, these can be carefully cut out before copying again.

(4) Allow to dry thoroughly. Then, using a fine black pen, carefully draw in any damaged or missing lines or lettering. For this I use a Uni/pen 0.3 fine line with waterproof, pigmented ink as this ink does not run or soak into the paper.

(5) Now, photocopy down to original size (A3-A4, A4-A5 or 71%) using the normal exposure setting on the machine. Copy twice, turning to keep square. It should now look as neat and clean as the original.

(6) The paper can be given an aged look by dipping the paper in a tea solution.

All of the above depends on the photocopier used and some experimentation will be found necessary. This is the method I have used to restore many diagrams in all sorts of conditions.

With a little care, a very neat and tidy label can be made which will finish off your restoration job nicely.

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