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Troubleshooting
Common Places to Look for Excessive Emissions
Each product is unique. However, there are common areas to watch for in
almost any product. Such places include:
Inside the box:
Long traces carrying digital signals
Microprocessors
Memory chips (including cache memory)
Disk controllers
Buffers
Any cable or cable assembly within the product
Switching power supplies
Displays
Outside the box:
Areas of the enclosure that are close to PCB trouble spots.
Any gaps or openings in the enclosure; vents; areas near buttons, jacks
or displays.; cables going through such openings.
All cable connectors and all cords normally connected to the product.
In general, at frequencies below 200-300 MHz, undesirable emission is
produced by cables connected to or extended from the product. At higher
frequencies the sources typically lie inside the product. Often, excessive
emissions radiate from a cable even though the cable itself doesn’t generate
the signal—it just acts as an antenna.
For board-level troubleshooting and diagnostics use the 3M
™
ScanEM-QC
Electromagnetic Near-Field Probe Kit, model CTK015.
