OPERATION
4-15
DRIVE SOURCE
1
2
34
A
B
Figure 4-7 Board Sectoring
• Connect the Drive Source Leads 10-20mm apart near one corner of the board
(Sector 3 in the illustration).
• Run the Trace Probe along the lines AB, then CD to determine if current is flowing
out of Sector 3 into the other sectors. If current is detected along these lines then it is
flowing into another sector. If so, alter the position of the Drive Source leads to a
different sector and repeat.
• Continue to move the Drive Source until no current is flowing out of the sector where
the Drive Source is connected. The position of the short is now somewhere within
that sector.
• Repeat the above process within that sector until the fault is isolated to within a
20mm square. Use of the circuit diagram, combined with knowledge of the current
path can often identify a likely place for a short (eg two adjacent IC pins).
Bus Faults (Stuck Nodes)
Where a static fault exists between two points that have no parallel capacitors, TRACE can be used to
locate the fault.
TRACE is usually unsuitable for locating Vcc loading faults, as power supplies are likely to have high
value electrolytic capacitors connected. These will produce misleading results because the capacitors will
conduct AC current from the Drive Source.
Bus lines have little or no capacitance so when one device is known to be holding the bus down, current
tracing is often the quickest way to isolate the fault.
The sectoring technique described previously is effective in most cases. However, it may be that the fault
is already known to be in one of five or six memory ICs, in which case there is a quicker method:
Artisan Technology Group - Quality Instrumentation ... Guaranteed | (888) 88-SOURCE | www.artisantg.com
To Next Page
Loading...
