The metal wire in the seat of the sensing disk and the mass of the blade (see figure below) must be electrically insulated from each other. Thus, if the continuity tester is used in the configuration shown in the picture, there has to be sound when touching the metal wire, no sound when touching any other part of the blade.
If the metal wire in the seat of the sensing disk and the mass of the blade are in electrical contact (rather than being insulated), when a DMT is executed the sound will be always on.
Please also examine pages 7, 37, 39 of the Bali Short Course 2001.
Similar electrical checks can be executed after having inserted spring, steel cylinder, sensing disk and quartz cylinder, using the layout on page 37 of the above reference, or even after having applied the membrane.
In case of short circuit (sound always on) possible reasons could be :
- A piece of metal is floating somewhere below the sensing disk (remedy: clean and blow compressed air)
- The inner longitudinal cable inside the blade (see p. 39 of the above reference) is broken and is in contact with the metal of the blade.
- The quartz cylinder has been forgotten – is missing.
Note that, if the spring or the steel cylinder are missing , then there will be no B (no sound in any position of the membrane).