HP 8901B - Page 278

Model 8901B Service
(.ls> Keyboard Key Check
1. Key in 60.0 SPCL. As the Special Function code is entered, 60.0 should appear in the display.
This indicates that the Controller responds
to keyboard interrupts. If faulty, see @ and (\/s> .
While the SPCL key is down, 35 should appear in the display. After releasing the SPCL key, 99
should appear in the display. If another number appears, continue on.
2. Jumper A13TP3 (INT) to A13TP15 (GND). This defeats the keyboard interrupt.
3. Press the keys one at a time and compare the display with the key codes shown in Figure 8D-8.
If a code other than 99 appears in the display with no key pressed, the key corresponding to the
displayed key code is probably stuck down; see Service Sheet 25.
If a wrong code appears for one
or more keys, check the corresponding key and decoder; see Service Sheet 25.
El
NO KEY PRESSED: 99
[301
Figure 80-8. Key Codes for Key Scan
@ Keyboard Interrupt Check
1. Connect high-impedance, dc coupled oscilloscope to A13TP3 (INT). The voltage should read a
TTL high. Pressing any key should result in a TTL low which should remain low for
40 to 60 ms
after the key is released.
If faulty, see Service Sheet 25 and check the Keystroke Detector.
@) Front-Panel LED Check
1. Perform the F’ront-Panel LED Check on Service Sheets 26 and 27.
@ HP-IB Check
1. See Service Sheet 28.
Nonvolatile Memory Backup Check
1. Measure A13TP13 (BATT) with a dc voltmeter. The voltages should be between 2.7 and 2.9 Vdc.
Repeat the measurement with POWER set
to STBY. The voltage should not change. If faulty,
see Service Sheet
24 and check the Nonvolatile Memory Supply.
Hint: The switching point between the normal and backup memory is adjustable. See Adjustment
22-Battery Backup
in Section 5.
Service Sheet BD5 8D-59