Printronix P4280, Руководство по обслуживанию

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3–25 Troubleshooting
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 to set the interface to
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 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.