HP Portable PLUS - Repairing the Display

8·26 Troubleshooting
Portable PLUS Computer
Table 8·8. Repairing the Display
Use this procedure if the VLCD supply voltage has already been checked and is good and the
system processors are operating,
but the display doesn't operate properly. If you make a repair at
any step, check whether the display seems to operate properly; if it does, go back to the main
diagnostic procedure in section 8.2.1.
....... OAD
LCD IJIfW..'
0000
Step
1. Using a scope, check for a 5-MHz signal,
50% duty cycle
(LCDCLK) at A2U23, pin 8.
2. Disconnect the keyboard cable from the
motherboard
PCA.
3. Using a scope, check for toggling output
signals
at A2U10, pins 12-16 and 18-20.
La) IJ8fW..I
0000
...........
'AIIJ.IIC
--
DAn
..........
0000
y
Response
If a good LCDCLK signal is present, go to step
2.
If signal is missing, verify that unit is turned on;
then check the signal at
A2U23, pin 8 again; if
the signal is bad, replace
A2U23.
If each signal toggles, go to step 4.
If any signal never toggles, check traces.
If A2U10, pins 16, 18, 19, and 20 are at OV, and
pins 12-15 are toggling, a software problem is
indicated-swap the motherboard PCA or
memory PCA to isolate the assembly.