Maintenance
Page 6-36
Service Manual
MT930B
AGC Adjustment
Adjustment Condition:
•
Input –30 dBm at 75
Ω
, 70 MHz CW to 70 MHz IF IN.
Adjustment Procedure:
1. Connect the spectrum analyzer to the 70 MHz IF (J204), and observe the
output level. Because the output impedance is 75
Ω
, be sure to account for
the insertion loss when using a conversion pad.
2. Turn on the AGC, and adjust R533 so the output level is –30
±
0.2 dBm.
3. Measure the DC voltage between J501 pin 3 and ground, and note this volt-
age (generally 6 to 8 V under normal conditions).
4. Connect the specified loop-thru cable between 70 MHz IN and OUT.
5. Input a –40 dBm signal and 75
Ω
at 1210 MHz CW to RF #1, and set to re-
ceive mode.
6. Adjust R574 so the DC voltage between JW05 pin 3 and ground is within
±
1 V, compared to the voltage read in step 3.
7. Connect a DC voltmeter between JW05 pin 11 and ground, and observe the
AGC voltage.
8. Set the input level for RF #1 to –60 dBm, and adjust R553 so the AGC volt-
age is 2
±
0.5 V.
9. Set the input level RF #1 to –20 dBm, and adjust R556 so the AGC voltage
is 8
±
1.0 V.
10. Repeat steps 7 and 8 two or three times.
11. Perform signal meter correction, using a separate procedure, and write the
corrected value.
Reference:
Unlike past SCC models, in addition to hardware (analog) adjustment, this model
also has software (digital) correction functions. Adjustment values for several
points are written after first adjusting to the specified operation points, using AGC
adjustment.
PLD Adjustment
Adjustment Procedure:
1. Apply a bit of solder to the cut land for testing pad to L301.
2. Connect J202 and J203 with a 50
Ω
coaxial cable.
3. Turn off the video modulation, connect a DC voltmeter to J301, and wait
about 10 seconds. Adjust R329 so the reading is within 0
±
0.02 V.
4. Set the video signal to sweep, and turn off pre-emphasis.
Summary of Contents for mt930b
Page 3: ...MT930B Service Manual Page i ...
Page 10: ...General Information Page 1 4 Service Manual MT930B THIS PAGE INTENTIONALLY LEFT BLANK ...
Page 22: ...Controls and Connections Page 3 4 Service Manual MT930B THIS PAGE INTENTIONALLY LEFT BLANK ...
Page 86: ...Options Maintenance Page 7 2 Service Manual MT930B THIS PAGE INTENTIONALLY LEFT BLANK ...
Page 90: ...Drawings Page 9 2 Service Manual MT930B 10264 Figure 9 1 MT930B Block Diagram 1 ...
Page 91: ...Drawings MT930B Service Manual Page 9 3 10265 Figure 9 2 MT930B Block Diagram 2 ...
Page 92: ...Drawings Page 9 4 Service Manual MT930B 10266 Figure 9 3 MT930B Block Diagram 3 ...
Page 93: ...Drawings MT930B Service Manual Page 9 5 10267 Figure 9 4 MT930B Block Diagram 4 ...
Page 94: ...Drawings Page 9 6 Service Manual MT930B 10268 Figure 9 5 MT930B Head Phone Schematic ...
Page 95: ...Drawings MT930B Service Manual Page 9 7 10269 Figure 9 6 MT930B RF PC Board Schematic ...
Page 96: ...Drawings Page 9 8 Service Manual MT930B 10270 Figure 9 7 MT930B Converter Module Schematic ...
Page 97: ...Drawings MT930B Service Manual Page 9 9 10271 Figure 9 8 MT930B Main PC Board Sheet 1 of 3 ...
Page 98: ...Drawings Page 9 10 Service Manual MT930B Figure 9 9 MT930B Main PC Board Sheet 2 of 3 ...
Page 99: ...Drawings MT930B Service Manual Page 9 11 10273 Figure 9 10 MT930B Main PC Board Sheet 3 of 3 ...
Page 100: ...Drawings Page 9 12 Service Manual MT930B 10274 Figure 9 11 MT930B Power Supply Schematic ...
Page 101: ...Drawings MT930B Service Manual Page 9 13 10275 Figure 9 12 MT930B IF Filter Block Schematic ...
Page 102: ...Drawings Page9 14 Service Manual MT930B 10276 Figure 9 13 MT930B Audio IF PB01 Schematic ...
Page 103: ...Drawings MT930B Service Manual Page 9 15 10277 Figure 9 14 MT930B Audio Out Schematic ...