Specifications

3–25Troubleshooting
on the CCB at C12 and D12, especially if they are absent. Garble
can also result from failed termination resistors or parallel logic,
but this is rare.
6. The 68010 LED never lights. The 68010 has not run its first instruction.
a. The first two programs PROMs may be malfunctioning or
inserted wrong. Do the corrective actions listed in step 4.d.
b. Check the power supply voltages: look at the control panel
display. If it is not blank, the logic power supply is okay. If the
display is blank, turn off the printer. Reseat the power supply
cable on the Mech Driver board and the CCB/Mech. Driver cable
assembly W1. Turn the printer on. If that does not correct the
problem, check for logic supply voltage on the CCB board
between the positive end of C4 (location A5) and TP1 (location
A1).
c. On the CCB, inspect the PROM sockets, the 68010 socket (if
installed), and the oscillator module at location P6. Remove any
obvious dirt or conductive dust.
d. Test for voltage supplied to the 68010 LED. The LED may have
failed.
e. If the failure persists, replace the common controller board
(CCB).
7. The 68010 LED lights, but never turns off. Look at the control panel
display:
a. If the top line of the display is blank, the control panel is
probably unplugged or defective. Do the corrective actions listed
in step 5.a.
b. If the display has a single line of black squares on the top line,
the 64180 has failed. Turn off the printer, remove the CCB, and
check the 64180 PROM at location H8 for bent pins, pins not
inserted, or backwards insertion. Discard any PROMs that were
inserted backwards. Their transistors were reverse biased, and
even if they work their service life has been shortened by thermal
damage. Replace the 64180 PROM. Check that the 64180 is
correctly inserted and completely seated in its socket.