QT4P16T: one path has no output, switching does not execute, or USB is not detected. Where do I start?
Work in layers. For a dead channel, first bypass the switch with a golden unit to separate a switch fault from an instrument or cable fault, then measure insertion loss and inspect the connector on that path. For a switch that will not execute, check the command chain: serial parameters, protocol syntax, and status readback — and note that USB and RS485 must not both send commands. For a USB device that is not detected, check the supply and cable first: the unit draws about 200 mA at 5 VDC.
Key points
- Golden-unit bypass first: it separates switch faults from instrument and cable faults
- Measure insertion loss on the suspect path and inspect the connector
- Check serial parameters, protocol syntax, and status readback before replacing hardware
- Never send commands over USB and RS485 at the same time
- Confirm the 5 VDC supply and try a different Type-C cable and port
- If it still fails, record the board serial and return it with the log
Products this applies to
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