HP Portable PLUS - Repairing the Serial Interface

8·30 Troubleshooting
Portable PLUS Computer
Table 8·10. Repairing the Serial Interface
Use this procedure if the diagnostic tests indicate a problem with the serial (RS-232) interface. If
you make a repair at any step, repeat the RS-232 test to see if the circuit is repaired; if it's good, go
back to the main diagnostic procedure in section 8.2.1.
Note: The RS-232 scope routine switches the interface circuit on and off while it's running.
The signals described in the steps below should be those observed while the circuit is
'on:
SUPPLY
PflOllL[H
SUPPLY
VOLT AGES
GOOO
CONTROL.
'5I GH "'LS
0000
Step
CONTROL/STATUS
~OelE"
1. Note the outcome of the RS-232 diagnostic
test.
2. Start the diagnostic module 'RS-232 Oscil-
loscope Routine' with the RS-232 test
connector installed. (Alternatively, use the
service disc scope routine.)
3. Monitor V + 232 while the RS-232 scope
routine is running:
A2U19 pin 14. (Use a
scope,
not a dc meter.)
4. Monitor V - 232 while the RS-232 scope
routine is running:
A2U19 pin 1. (Use a
scope, not a dc meter.)
DATA PAtH
PR08LiEJoI
Response
If any of the CTS, DSR, DTR, RTS, Carrier De-
tect, or Ring Detect lines are indicated bad, go to
step 2
If the Transmit or Receive Data lines are indi-
cated bad, skip to step 6.
If 'Power Supply Stuck On' is indicated, go to
step
2.
If V+232 is at the same voltage as VBAT, go to
step
4. (If 'Power Supply Stuck On' was indi-
cated, repeat the RS-232 test instead.)
If V + 232 is bad, check continuity to the battery.
If V-232 is more negative than -6 Vdc, go to
step 5.
(If 'Power Supply Stuck On' was indi-
cated, repeat the RS-232 test instead.)
If V - 232 is outside its range, skip to step 8.