No Video or Unstable Raster

Normal startup boot chime, the LED is on, and the hard drive starts up. The display, however, is solid gray.

Possible Cause

Possible Fix

Corrupted PRAM.

- Reset parameter RAM. Hold down <Command> <Option> <P> <R> during startup before "Welcome to Macintosh" appears.

Corrupted system software.

- Boot off the system CD that came with the unit. Do you see a normal screen display now? Yes: Reinstall system software. (You must use the system software CD that came with the unit to get the correct version of Mac OS.) No: Go to next step.

The PMU chip or logic board needs to be reset.

  • Press the PMU chip on the logic board with the AC power cord disconnected. (See "The PMU Chip" and "Resetting the PMU on the Logic Board" mentioned earlier in this chapter.)
  • Connect the power cord and power on the system again.

Do you have power to the system now? Yes: Test the unit with MacTest Pro and return the computer to the customer. No: Plug in the AC power cord and reset the PMU chip again. Do you have power to the system now? Yes: The battery is likely bad, check the battery. No: Go to the next step.

Bad video cable connection.

- Verify that the CRT video board cables, the RGB cable, and P701 (the deflection yoke cable on the power/ analog board) are securely attached. If the problem persists go on to the next step.

Bent CRT neck pins.

- Remove the CRT video board. Check that the pins on the CRT neck are not bent. Carefully reseat the CRT video board and power on the computer. Do you have video now?

Yes: Run MacTest Pro and return the computer to the customer. No: Go on to the next step.

Normal startup boot chime, the LED is on, and the hard drive starts up. The display, however, is solid gray.

Possible Cause

Possible Fix

Bad power/analog/video board

- Check for trickle power on the logic board (Refer to "Testing J9 for +5 V Trickle Power on the Logic Board" mentioned earlier in this chapter). Trickle power is present as soon as the power cord is plugged into the computer.

Did you measure +5 V trickle power on pin 1 of connector J9? Yes: Go to the next step.

No: Refer to the troubleshooting symptom "No Power".

Bad logic board

Check for DCO voltage at location C10 on the logic board (Refer to "Testing DCO (Down Converter On) Voltage at C10 on the Logic Board") mentioned earlier in this chapter). Did you measure approximately -1.2 volts?

Yes: Go to the next step.

No: Replace the logic board.

Bad internal RGB video cable.

  • Replace the internal RGB video cable that attaches to the power/analog/video board and to the logic board. The cable is screwed to the power/analog board, located near the AC power plug on the power/analog board.
  • If this doesn't solve the problem, go to the next step.

Bad power/analog/video

- Replace the power/analog/video board.

Bad CRT.

- Replace the CRT.

Was this article helpful?

0 0

Post a comment