Service manual

Troubleshooting Tables
4-11
Printed data are garbled. A printer cable is not fully seated.
Defective printhead.
Defective component in data path.
Reseat connector J304.
Replace printhead assembly.
1.Replace printhead control cable.
2. Replace CPU assembly.
Poor print quality or some dots not printing. Dirty printhead.
Loose ESD brush fibers.
Incorrect printhead or sensor cable
routing.
Defective printhead or printhead
cables.
Defective component in printer cir-
cuitry.
Clean printhead.
Remove loose brush fibers and clean
printhead.
Make sure there is slack in the printhead
cables.
Replace printhead assembly or printhead
cables.
Replace CPU assembly.
Some dots always on. Defective printhead.
Defective printhead or printhead
cables.
Replace printhead assembly.
Replace printhead assembly or printhead
cables.
Table 4-5 Printer
Symptom Possible Cause Corrective Action
Table 4-6 Keyboard and Display (LCD)
Symptom Possible Cause Corrective Action
Display stays blank or all
black. (M1770A/M1771A
only)
Contrast misadjusted.
Keyboard cable is not fully seated.
No power being supplied to keyboard assem-
bly.
Defective keyboard assembly.
Defective LCD assembly
Defective contrast control in CPU assembly.
Adjust contrast using the and . or
keys.
Reseat keyboard cable.
Test power supply. Replace if defective.
Replace keyboard assembly.
Replace LCD assembly.
Replace CPU assembly.
Keys won’t work. Unable to
enter data or operate controls.
Keyboard cable unplugged.
Keyboard circuit board defective.
CPU assembly defective.
Reconnect keyboard cable.
Replace keyboard assembly.
Replace CPU assembly.
Garbled data on display. Keyboard cable not seated correctly.
Keyboard flex cable connection is poor.
Defective LCD.
Defective keyboard assembly.
Defective CPU assembly.
Make sure cable from keyboard to CPU assem-
bly is properly seated.
Make sure flex cable is fully inserted and locked
in each connector.
Replace LCD assembly.
Replace keyboard assembly.
Replace CPU assembly.
Shift