Tektronix WFM8200, Service Manual

Page: 54 / 85

General Maintenance
LCD Troubleshooting Perform this test if there is no display on the LCD, but the power supplies test as
nominal.
1. Connect an external XGA monitor to the “Display” output on the rear of the
instrument.
2. Cycle the power and watch the external monitor. If the monitor does not
display the boot up messages and normal operational screen, replace the
main board.
3. If the external monitor does show the nominal screen, check the gray ribbon
cable from the internal display to J17 on the main board. This carries the
XGA data to the display.
4. If the gray ribbon cable is OK, check to see if the backlight is on. Look into
the vent holes along the left side of the bezel while you cycle the power. You
should see the backlight come on when power is reapplied. It may help to be
in a low light area to see the backlight.
5. If the backlight is on, replace the front panel assembly.
6. If the backlight is not on, check the backlight power cable from the backlight
inverter (on the rear of the display assembly) to the main board J18. Also
check connector J18 itself for any solder issues.
7. If the backlight is still bad, replace the front panel assembly – although there
is still a small chance the problem is in the main board.
Audio Power-Up
Diagnostic Failure
It is sometimes dif fi cult to isolate the root cause of audio problems. Most audio
problems are due to faults on the audio board, but the audio board communicates
with the main board, so in some cases the problem may be there as well.
Audio Power-up Diagnostic Detailed Information. The Power-up Diagnostic does
the following:
Reads all of the AES decoder internal registers and veri fi es that what is read
is correct
Reads all of the D/A internal registers and veri fi es that what was read is correct
Performs an active-bit test on the A/D output clocks
Checks the serial EEPROM to see which of the analog inputs have been
calibrated
Tests the Audio DSP/FPGA interface
The main CPU detects if the DSP heartbeat fails. This condition will be
shown in the diagnostic log
4–14 WFM8200 and WFM8300 Waveform Monitors Service Manual