4-1
SECTION 4 – OPERATION
LOCATING FAULTS WITH THE TONEOHM 950
4.1 Range selection
Different types of short circuit and loading fault require different location techniques. It is often possible to
find the fault in more than one way, but the following approach is recommended. In some cases a
combination of techniques may be required.
When selecting the range to use, consider the following questions:
• Is the fault a low resistance short (i.e. less than 200 mΩ)?
• Is the fault static or dynamic, i.e. is the fault always present (static) or only present
when the board is powered (dynamic)?
Track Resistance is applicable to locating static, low resistance shorts on single or two-sided boards.
If the fault is dynamic then use either Track Current or Track Voltage. Using Track Current provides a
direct display of the current flowing in a track, but on very low resistance (wide) tracks it may be
necessary to use Track Voltage.
• Are the tracks or cables associated with the short accessible?
If access is difficult (e.g. a wire harness or densely packed memory bank) the Current Trace Probe is
useful, as it can detect current without making contact.
• Does the short involve a plane in a multi-layer board?
If the short involves a plane, then the PLANE SHORTS range is the optimum range to use. However, if
the fault is dynamic it will be necessary to use either Track Current or Track Voltage.
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