TONEOHM 950 OPERATOR MANUAL
4-14
The DRIVE SOURCE LED indicates flow of Drive Source current. If the LED does not light, either the
leads are connected incorrectly, or there may be insufficient current flowing for the Current Trace Probe to
detect the resulting field.
• Hold the Current Trace Probe near one of the Drive Source leads. As the probe
approaches the lead, the LCD reading and the tone frequency should increase.
• Position the probe for a maximum reading against one of the Drive Source leads.
• Adjust the DRIVE SOURCE control to give a reading of 100 to 130. If the reading is
less than 100, leave the control at maximum (this occurs with high resistance shorts,
i.e. above 150 Ω).
• To alter the distance over which the probe detects current, adjust the DRIVE
SOURCE control.
Operation
Unlike the milliohm ranges, when using TRACE the probe does not gradually approach the fault, giving a
highest tone when it is reached. Instead the probe shows the path of the current. Since the reading and
tone are proportional to the detected field, it is evident when the probe is moving away from the current
carrying track.
When using the Trace Probe take care not to detect the magnetic field from the Drive Source leads
draped over the PCB.
When using TRACE, the following should be considered as a primary objective:
Find a position where the Drive Source leads can be clipped on the board under test, such that
the Trace Probe detects no field outside a 15 to 20mm square adjacent to the leads. This will
mean that the fault must be within that square.
Trying to locate the fault without moving the Drive Source leads is usually unsuccessful without some
familiarity with the PCB layout. A recommended approach is to move the injection points of the Drive
Source around the board to determine in which regions there is current flowing.
The board is first divided into four sectors (see Figure 4-7).
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