Standard Communications mt930b, Service Manual

Page: 71 / 155

Maintenance
MT930B Service Manual Page 6-39
•
Pre-emphasis: 525
•
Frequency Deviation: 27.6 MHz p-p
• Condition 3: Video signal: PAL
•
Pre-emphasis: 625
•
Frequency Deviation: 16.0 MHz p-p
• Condition 4: Video signal: PAL
•
Pre-emphasis: 625
•
Frequency Deviation: 24.0 MHz p-p
Adjustment Procedure:
1. Set the UUT to receive mode, connect a video analyzer to VIDEO #1 and
COMPOSITE OUT, and measure the video characteristics.
Use 27 MHz for IF BW when using settings for Conditions 1 or 2, and use
36 MHz for Conditions 3 or 4.
When de-emphasis is 525 under Conditions 1 or 2, use 4.2 MHz for the filter.
When de-emphasis is 625 under Conditions 3 or 4, use 5.5 MHz for the filter.
When the video level is set for Conditions 1 or 2, adjust so the bar level is
100 ± 1 IRE
When the video level is set for Conditions 3 or 4, adjust so the bar level is
700 ± 7 mV.
2. Set the video analyzer to DG/DP, and check that the latest specifications are
satisfied when average picture level (APL) is set to any of 10%, 50%, or
90%. Check both C and Ku bands.
3. If the specifications are not met in step 2, readjust IF filter PH01. Effective
adjustment locations follow:
a. Use LF76 and LF77 when IF BW is 36 MHz under Ku-NOR (or C-INV).
b. Use LF36 and LF37 when IF BW is 36 MHz under C-NOR (or Ku-INV).
c. Use LF56 and LF57 when IF BW is 27 MHz under Ku-NOR (or C-INV).
d. Use LF16 and LF17 when IF BW is 27 MHz under C-NOR (or Ku-INV).
In all cases, check the video characteristics by turning both of the corre-
sponding coil cores in the same direction either CW or CCW. The rotation
angle should generally be 45 degrees or less. If turned more than this, re-
check the pass-thru characteristics of the IF filter.