6 Instruments and conventions for performing diagnosis and repair
3.4) Conventions
By convention, when a measurement has to be taken between
two points, for example a b , the arrow point indicates
where to apply the red tip of the multimeter (a),while the black
tip is applied at the other end (b).
When a double arrow appears between two measuring points
(e.g.: c d ), the voltage to be measured is alternating
(normally at 50 Hz), therefore it does not matter in which order
the multimeter terminals are applied.
In drawings and tables, when a voltage measurement appears
referring to terminals of components such as DIODES, BJT,
MOSFET and IGBT, the multimeter is used in "diode test" mode
(these measurements are always taken with the machine swit-
ched off and normally give values in the range + 0.10 … + 0.90
Vdc). In this case the following symbol is affixed beside the
value to be measured
Junction measurement (multimeter in "diode test" mode)
The following symbols will be used in the same way:
AC or DC voltage measurement (multimeter in voltmeter
mode)
Resistance measurement (multimeter in ohmmeter mode)
Current measurement (ammeter clamp or shunt + multi-
meter in millivoltmeter mode)
Frequency measurement (multimeter in frequency meter
mode)
The measuring conditions (power source on/off, MMA/TIG ope-
rating mode, etc.) are always clearly indicated beside the values
to be measured.
In the tables the various auxiliary power supply voltages are
marked with the initials V1, V2, etc. to permit identification
when present in several boards. When a power supply voltage
derives from another one, the second takes the name of the first
with the addition of a letter in increasing order (e.g.: V1a, V1b,
etc.). In these cases, all the derived voltages have the same earth
in common.
The connector terminals are indicated by the name of the con-
nector followed by a slash and the number of the terminal; for
example CN1/2 indicates terminal 2 of connector CN1.
Unless otherwise specified, all the measurements must be per-
formed with the boards fitted, together with their connections.
Remember that the first of the tests to be perfor-
med is the VISUAL CHECK!
The visual check reduces troubleshooting times
and directs any subsequent tests towards the
damaged part!
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