HP 8
Service Guide
Microprocessor Board
The following checks can be performed on
Microprocessor Board:
Check
Procedure
Visual
Inspect
board carefully for dry joints, unsoldered
joints, or broken components
Clock
an Oscilloscope,
check
that there is a clock signal
at the
pin (66) on the Microprocessor. The
frequency should be 16.78 MHz (8.38 during reset).
If a clock signal is not found check crystal
and
its
associated components. Also check C44, C49 and C66,
capacitors used in the VCO circuit
DIP Switches
HP-IB
Dividers
Check that the switches on SW1 are set, according to the
following table:
5-4. Settings for DIP Switch Sl
Note that Section 1 in the DIP
Switch
disconnects the
Microprocessor clock line, and incorrect setting, or a
faulty switch section disables the Microprocessor
If faults are suspected in connection with the HP-IB
Interface, check the ribbon cable that joins the HP-IB
socket to the Microprocessor Board. Using a resistance
meter,
check
for continuity along each of the ribbon
cable conductors
Dividers
and
divide the system clock
to produce a clock for the HP-IB Interface. Use an
oscilloscope to check operation. Pin 3 on U28 is clock
input (16.78 MHz). Pin 5 gives the first divide-by-2
output (8.39 MHz) and pin 9 provides the final clock to
the HP-IB IC, just over 4 MHz.
is a 3 V Lithium battery, type: Panasonic
V CR2477. Its HP part number is 1420-0394. It is
capable of in excess of 5 years’ operation. Using a
high impedance voltmeter measure across the battery
terminals. If you suspect that the battery is faulty,
change by unsoldering it from the PC Board.
Troubleshooting
