Tektronix WVR8200, Руководство по обслуживанию

Страница: 57 / 78

General Maintenance
Isolating Lissajous Display
Errors
The audio Lissajous phase display uses a serial data path between the audio and
main boards. A failure in this data path can be due to a problem on either board.
Perform the following tests to isolate the problem to one board or the other.
1. Prepare a test oscilloscope with the following settings:
Control Setting
Vertical Scale 2.00 V/div
Horizontal Scale 200 ns/div
2. Check the Lissajous bus clock by performing the following substeps:
a. Put the oscilloscope probe on pin 62 of connector J200 on the audio
board. Verify the signal is
≈ 3 V
p-p
and is a continuous 50% duty-cycle
squarewave.
b. If the signal at J200 is not as described in step a, the audio board most
likely has a failure; otherwise, proceed to step c.
c. With the oscilloscope probe, verify the signal at J26 pin 62 of the main
board is as described in step a. If it not as described, suspect the cable; if
it is as described, replace the main board.
3. Check the Lissajous bus frame and data signals by performing these substeps:
a. Put the oscilloscope probe on connector J200 pin 61 of the audio board
and verify the signal is
≈ 3 V
p-p
and toggles low at regular intervals.
b. If the signal on pin 61 looks OK, put the oscilloscope probe on pin 63.
Pin 63 is the data line and the signal will have a somewhat random look
depending on the audio source. Just verify that the signal is toggling and
is
≈ 3 V
p-p
.
c. If either signal looks bad at J200, the audio board most likely has a failure,
otherwise proceed to step d. With the oscilloscope probe, check the signal
at pin 61 of J27 on the main board. Verify the signal is
≈ 3 V
p-p
and toggles
low at regular intervals.
d. If the signal on pin 61 looks OK, put the oscilloscope probe on pin 63.
Pin 63 is the data line and the signal will have a somewhat random look
depending on the audio source. Verify that the signal is toggling and is
≈ 3 V
p-p
.
e. If either signal is bad, suspect the cable; otherwise replace the main board.
WVR8200 and WVR8300 Waveform Rasterizers Service Manual 4–17