Service manual

51
Trigger Circuit Troubleshooting (Figure 3-8)
The Multiple Electronic Load can be triggered over the HPIB using the GET function, the *TRIG common command, or
the TRIG subsystem HPSL command. The TRIG subsystem lets you select either the ac line frequency, internal timer, or
TRIG command as the trigger source. There is also an external TRIGGER input on the mainframe for external trigger
inputs.
Troubleshooting the trigger circuit consists of sending commands or running programs that generate signal pulses in the
direction indicated in the following discussion (also refer to Figure 3-8). If a signal does not toggle where indicated, the IC
or gate that generates that signal is probably defective.
AC Line Triggers
First use an oscilloscope to check that the waveforms at U243-14 and Q211-11 are correct.
If the waveform is correct, send string "TRIG:SOUR LINE" and check the GPIB board as follows:
U208-9 (LSNK_EN) goes high
U247-11 (TRIG)
U219-13 (TRIG_OUT)
U215-11 (PRI_TRIG)
U219-10
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toggle at
line frequency
On the module Control board, check that:
U318 pins 1,2,3,9,10,11,13, all toggle at the line frequency.
Note: An ac line frequency of 60Hz produces a trigger period of 16.67ms; 50Hz produce a trigger period of
20ms.
Internal Timer Triggers
Send the string "TRlG:SOUR TIM" and check the GPIB board as follows:
U228-12 (TRIG_EN) goes high
U207-6 goes low
U219-9 becomes active
U215-11 (PRI_TRIG) pulses @ 1ms intervals
Note: On the module Control board, observe that U318 pins 1,2,3,9,10,11,13, also pulse at 1ms intervals.
Next send the string "TRIG:TIM 1" or "TRIG:SOUR TIM;:TRIG:TIM 1" and check that PRI_TRIG (U215-11) pulses low
at 1ms intervals.