Specifications

4–25Troubleshooting
f. If the printer prints garbled data or slews uncontrollably, put the
printer into hex dump mode and analyze the binary data. One cause
of garble is the host interface or cable is not transmitting all the data.
When this occurs, the Centronics or Dataproducts interface receives
a 1 on every unconnected data line. Uncontrolled slewing is often
caused by enabling PI (Paper Instruction) when the host lacks a PI
signal. (PI shows as “p” on the hex dump.) Some DEC RS–232 and
Dataproducts interfaces only send 7 data bits. In this case, the eighth
bit will be received as one.
In RS–232, a common cause of garble is the interface configured at
the wrong baud rate or parity. Sometimes the host sends 1.5 or 2 stop
bits; in this case, the printer’s “1–stop–bit” setting will accept both
1.5 and 2 stop bit data. Sometimes the data may “fade” or “persist”
from one character to the next. This reveals a problem with
Centronics or Dataproducts terminating resistors on the CCB at C12
and D12, especially if they are absent. Garble can also result from
failed terminating resistors or parallel logic, but this is rare.
5. The DPU 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 3.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 DPU LED. The LED may have
failed.
e. If the failure persists, replace the common controller board (CCB).