Hints. - When a board has been plugged, check that you have:
1. 13 plugs the right way and 13 upside down.
2. Check that all plugs are firmly in position.
Continuity and Short tests should be made before the job has been plugged.
A quick way of finding open circuits is to plug a trolley to the enigma
concerned. If a plug from the U/W is removed 2 lights should go out. If
only one extinguishes this must be in the same circuit as the one already
"D U/W" with its serial number must be clearly shown on the Job
and Checking Sheets and entered into Log Books. Operators should not strip D
Shorts on U/W Boards, - If, when short testing a machine which
is using D boards, a short is indicated between two enigmas, it is more
likely to be caused by two adjacent contacts touching on the U/W. Using the
trolley in the orthodox manner it is difficult to isolate the fault but this
can be overcome quite easily by a slight deviation. Having localized the
fault to two enigmas, isolate them by removing the coupling jacks and
proceed as follows:
Plug the top lead from the trolley to one end of the first
enigma, and the bottom lead to one end of the second. The only possible
continuity between the two enigmas is through The short and this will show
by lighting one lamp on the trolley. If straight drums are put on the first
enigma then the lamp will indicate the faulty letter on the U/W. By
reversing the trolley input and putting the straight drums on the second
enigma, the shorted letter on this enigma will be indicated. The plug of
the letter in question can now be inspected on the U/W in the usual way.