Maintenance
MT930B
Service
Manual Page 6-43
Audio VCO Adjustment
Adjustment Procedure:
1. Connect a DC voltmeter between pins 1 and 5 of J11, and observe the tun-
ing voltage.
2. Set the audio subcarrier frequency of #1 to 50 kHz, and adjust LB11 so the
tuning voltage is 2
±
0.1 V.
3. Set the audio subcarrier frequency of #1 to 9995 kHz, and adjust LB11 so
the tuning voltage is 10.5
±
1 V.
4. Connect a DC voltmeter between pins 1 and 5 of J41, and observe the tun-
ing voltage.
5. Set the audio subcarrier frequency of #2 to 50 kHz, and adjust LB41 so the
tuning voltage is 2
±
0.1 V.
6. Set the audio subcarrier frequency of #2 to 9995 kHz, and adjust LB41 so
the tuning voltage is 10.5
±
1 V.
7. Connect a DC voltmeter between pins 1 and 5 of J71, and observe the tun-
ing voltage.
8. Set the audio subcarrier frequency of #3 to 50 kHz, and adjust LB71 so the
tuning voltage is 2
±
0.1 V.
9. Set the audio subcarrier frequency of #3 to 9995 kHz, and adjust LB71 so
the tuning voltage is 10.5
±
1 V.
Audio Discriminator Adjustment
Adjustment Conditions:
•
Set the FM signal generator as follows and the input to JB01:
•
Carrier signal: 6.8 MHz
•
Output level: –9
±
1 dBm
•
Modulation signal: 1 kHz
•
Frequency Deviation:
±
16 MHz p-p
•
For each of AUDIO #1, #2, and #3, set as follows:
•
Subcarrier frequency: 6800 kHz
•
Output level: 100
•
De-emphasis: FLAT
Adjustment Procedure
10. Put the UUT in receive mode, and set the BW to 440 kHz for #1 and to
880 kHz for #2 and #3.
11. Connect the DC voltmeter (dual-polarity) between pins 2 and 3 of JA11, and
observe the voltage.
12. Connect the audio analyzer to AUDIO #1.
13. Adjust LA11 so the voltmeter reading is 0
±
10 mV.
14. Adjust LA12 so the distortion ratio is minimized.
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 ...