Specifications

4–26 Troubleshooting
6. The DPU 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 4.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 RTPU 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 RTPU PROM. Check that the 64180 is correctly
inserted and completely seated in its socket.
c. If the display reads “Diagnostic Test in Progress” and DPU LED
has been on for 20 seconds or more but is not blinking, it means
the 64180 cannot communicate with the 8032 on the Mech Driver
board. Turn off the printer, reseat the cable in J2 of the CCB and on
the Mech Driver board. Check the 8032 on the Mech Driver, its
PROM, and its clock jumper (E1–E2) for correct insertion, bent pins,
etc. Reseat the jumper and socketed parts. If the problem persists,
replace the Mech Driver’s PROM and the CCB/Mech. Driver cable
assembly W1.