Interdigital pause; with older exchange equipment, a pause was necessary between digits, to allow the central office equipment to advance itself. This pause is equal to the time it takes the dial to return to normal after completing the pulsing operation, and is equal to two blanks (see the space between the #1 and the fingerstop). British dials have three blanks in this area: this is because older British equipment required somewhat longer time to function.

Off-normal springs: The additional springs on a dial "short" the receiver circuit (except, that in earlier WECo dials terminals “W" and "BB" opened the receiver circuit). The off-normals operate when the dial is rotated, to prevent the clicks from being heard by the calling party.

Speed: Except for certain dials intended for use in PBX boards the usual speed for a dial is "10 pulses per second" (or about the time it takes to say 1002)... that is, the dial, when fully rotated, should take about I second to return to normal, when released. So called "high speed" dials (20 pps) can only be used with panel, electronic, crossbar or digital systems; and 10 pps dials MUST be used with (now rare) Step-by-step central office technology.

Dials, Repair, Maintenance

Generally, relatively sophisticated equipment is required for dial repair. GTE practices suggest dismantling the entire dial; this is hardly feasible today.

WD-40 can be used to free a seized dial, but its use is NOT recommended. WD-40 is not a permanent lubricant (it eventually evaporates), The manufacturers provide a number of practices on dial lubrication. but it was interesting to note that in Northern Electric's Repair and overhaul shops their own practices were ignored, The dial repair person simply used a toothpick, dipped about 1 /4" into a small container of sewing machine oil (3 in 1 for example). Each bearing point is lubricated, with care being taken to see that absolutely NO oil gets into the governor. DO NOT APPLY EXCESS OIL. (At this point, if the dial didn't turn at an approximately close speed, Northern simply junked it!

Assuming the dial rotates, the speed can be adjusted. The governor on the AECO style of dial is easiest to work on; if the dial is running slow simply bend the governor springs in slightly (a little at a time!) ... likewise, if running fast, vice versa. Nmbrs. 2, 4 and 5 type dials have a small screw in the governor case; loosen the screw and adjust the little dial to the left or right to adjust the speed; then retighten the screw. Late model WECo design dials are not as readily adjusted. It is necessary to remove the spring that holds the weights (on the governor) and open or close the arc, slightly; this may prove near impossible in some cases.

The shunt springs on a dial are best checked with a buzzer. An ohmmeter does not draw adequate current, and marginal off-normal contacts may test OK. With a buzzer and battery connected to (for example) the white leads of a #7D dial, the buzzer should buzz with the dial turned less than 50% of the diameter of the finger holes. 

If a dial dials wrong numbers, it generally means that too many pulses are being sent. It is important on 6, 7 and similar dials that the pulsing cam is on the correct angle; compare with a known good unit. On AECO dials, the location of the cam that operates the "blanking" spring is all important; an AECO dial actually pulses one additional pulse, but this last pulse is supposed to be shunted by the blanking spring. With an electronic switching center, the slightest interruption is counted as a pulse; thus the blanking spring must be accurately adjusted.