HP Portable PLUS - Using Oscilloscope Routines

Portable PLUS Computer
Troubleshooting 8-33
Table 8-11. Repairing the Modem (Continued)
Step
4. Monitor the modem clock signal while the
modem scope routine is running: A3U11,
pin 8. (Use a scope.)
5. Monitor MSOUT at A3J2, pin 4 while the
modem scope routine is running .
6. Monitor MSIN at A3J2, pin 6 while the
modem scope routine is running.
1
7. Swap the modem PCA, then recheck the
operation. (Alternative: trace signals
through the circuit using
the schematic dia-
grams in figures 12-5 and 12-8 and replace
faulty components.)
Response
If the modem clock oscillates at 4.6 MHz while
the circuit is
• on: this signal is good; go to step
7.
If the modem clock doesn't oscillate at 4.6 MHz,
replace
A3U11.
If this signal does /lot toggle, trace it back to
A2U16, pin 25 on the motherboard PCA. If
MSOUT still does not toggle, replace A2U16 (or
the motherboard
PCA).
If MSOUT at A3J2, pin 4 does toggle, check
MSOUT at buffer A3U1 , pin 12. If A3U1, pin
12 does
/lot toggle, replace A3U1; else check the
demodulator A3U3, pin 21 to verify that it also
toggles.
If not, replace A3U3 or the modem
PCA.
If MSIN toggles, trace the signal back to A2U16,
pin 45 (on the motherboard PCA). If the MSIN
signal at
A2U16, pin 45 does not toggle, replace
A2U16 or the motherboard PCA.
If MSIN at A3J2, pin 6 does not toggle, check
the signal at the gate of A3Q2.
If MSIN at the
gate of A3Q2 does /lot toggle, replace demodu-
lator IC A3U3. If this signal does toggle, replace
A3Q2 or the modem
PCA.
Replace the motherboard PCA or modem PCA,
as indicated.
8.3 Using Oscilloscope Routines
You can use osciIIoscope routines to isolate and verify problems while performing component-level
repair
on the Portable PLUS, including troubleshooting a unit that doesn't turn on . This section de-
scribes the procedure for setting up and using the scope routines.
In order to use these routines, you'll
need the following equipment (as listed in chapter 1):
• HP 180C/1801A/1820C osciIIoscope (or equivalent).
• HP 10004 osciIIoscope probe (or equivalent).
• Diagnostic module (part number 45711-60910).
• Keyboard extension cable (part number 45711-60907).
•
LCD extension cable (part number 45711-60908).
• RS -232 test connector (part number 00090-60914).