Service manual

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Figure 3-10. Overpower Circuit Troubleshooting
Fan Speed Control Troubleshooting (Figure 3-11)
Use extreme caution when troubleshooting the GPIB board when it is removed from the mainframe while
connected to AC line voltage. AC line voltage is present throughout the fan speed control circuit located on
the lower third of the board. Although removed from the mainframe, the GPIB board must remain
connected to the transformer cable, the fan cable, and the line switch cable. The safety interlock switch
must also be engaged.
Figure 3-11 is the main troubleshooting tool if the fans are not running or if they do not change speed. Note that a Agilent
6050A mainframe with three or fewer single-width modules installed will not turn fan #2 on. Fan #2 is turned on only when
there are four or more single-width modules installed.
If the fans are not running, or if they continually run at top speed, remove the GPIB board from the mainframe and use an
oscilloscope to check the waveforms in Figure 3-11. Start with the waveform at the fan and work back to the control circuits
to locate the defective part. The waveform at U243-1 is the normal power-on waveform.