Agilent Technologies 2948 manual A2 Digital Assembly to A5 Display Assembly Interface, Description

Model 8904A Service

A2 DIGITAL ASSEMBLY TO A5 DISPLAY ASSEMBLY INTERFACE

Description

A failure in the A5 Display Assembly can cause the entire instrument to hang up at power up. If this condition is suspected, measure pin 12 of A2U25 or pin 4 of A2U20 with a high impedance, dc coupled oscilloscope. TTL pulses should be seen with 1 ps high and 15 ps low. (The signal is normally a TTL high.)

To check the backlighting, measure the connection of the red wire at A2J8 with a high impedance, dc coupled oscilloscope. (A2J8 is located in the extreme front, right side of A2.) An ac waveform of 80 to 300 Vpp should be observed. The period should be approximately 2 ms. The amplitude will vary with brightness of the display and is adjustable. (See Adjustment 5, Display Backlighting and Contrast in Section 5 of the Operation and Calibration Manual. Display contrast is also adjustable.)

Note that high voltages are measured.

Ano load or short on the backlighting oscillator of A2 will damage the drive circuit.

NOTE

The display backlighting automatically turns off approximately 3 minutes after the last keystroke. Pressing any key will turn the backlighting back on.

Troubleshooting (DigitalDisplay Interface) 8-41