HP Integral Personal Computer Service Manual page 137

8-..
Troubl ..... otl ... and DllIgnoetlca
T ..... 1-17. Trouble.hootinl the Prlntar ROil, RAM, and CPU (Continuad)
Step
4. Repeat the procedure for pins 17, 18, 19,
22, and 23 of U28 on the logic B PCA. In
each case, tum off the power, connect a
logic probe to the pin, then turn on the
power and watch for a pulse after about one
second.
I
Indicated Action
If a pulse occurs on pin 17 of U28 (DOT 11), an
internal ROM failure
is
indicated. Replace U28
on the logic
B
PCA.
If a pulse occurs on pin 18 of U28 (DOT 10), an
internal RAM failure is indicated. Replace U28
on the logic B PCA.
If a pulse occurs on pin 19 of U28 (DOT 9), a
timer failure is indicated. Replace U28 on the
logic
B
PCA.
If a pulse occurs on pin 22 of U28 (DOT 6), an
external RAM failure is indicated. Replace U27
on the logic B PCA.
If a pulse occurs on pin 23 of U28 (DOT 5), an
external ROM failure is indicated. Replace U32
on the logic B PCA (localized for some
languages).
Tldtle "18. Troubl . . hootlng the· Carrl ..... otor Circuitry
If you have trouble with the carriage, check that the ROM, RAM, CPU, power supply, switch panel,
and carriage motor are operational, then troubleshoot the carriage-motor circuitry as follows using a
logic probe.
(If
you have not already done so, prepare the computer to troubleshoot the logic B PCA
as
described in table 8-27.)
In each of these steps, always turn off the power before you connect or
disconnect a cable
or
replace a component.
Nota.
The operating system ROM must be installed in the computer during the tests that
follow, and paper must be installed in the printer.
Stap
1. Probe pins 4, 5, 6, and 7 of U28 on the logic
B PCA, each in turn, while you press the
top~f-form
button (the square, white but-
ton on the switch panel).
Ie Probe pins 8 and 10 of U29 and pins 8 and
10 of U30
on the
logic B PCA, each in turn,
while you press the top-oi-form button.
I
Inellcatad Action
If any pin fails to toggle several times~ replace
U28.
If any pin fails to toggle, replace the cor-
responding IC.
If the carriage moves with difficulty and then
stops after a few seconds, or if there appear to
be slight variations in the width of the printed
characters, check CRa, C26, CR9, and C27 on
the logic B peA for opens and shorts.
If
you re-
place an open diode, replace the corresponding
capacitor as well.