Model: IC-751A Division: Amateur Note: This service bulletin is meant for technical per- sonnel with experience working on solid state com- munications equipment. Damage caused by im- properly installing this modification may cause ICOM to charge for subsequent repairs to the product. ICOM does not warrant this modification. Bulletin #: 28Oct86-08 Date: October 28, 1986 Subject: Gain improvement of noise blanker in narrow mode Procedure 1. Replace R42 (currently 150K) on the main board with a 100K resistor. Bulletin #: 28Oct86-09 Date: October 28, 1989 Subject: Passband tuning improvement Procedure 1. Replace R335 (currently 1M) on the main board with a 3.3 M resistor. Bulletin #: 22987-001A Subject: Correction for IC-751A service manual Corrections 1. Changes to section 6-3 Adjustment Points BFO Frequency Current Correction Step 2 LSB Mode L34 L33 Step 3 CW Mode L33 L34 Switch Settings Current Correction Step 9 RTTY Mode S1 S2 S2 S1 Step 10 S2 S1 Bulletin #: 13889-010 Date: May 1, 1989 Subject: Reduce intermodulation from FM stations (70-108 MHz) and TV stations (165-245 MHz) Procedure Write to ICOM's customer service department for a copy of this service bulletin. Bulletin #: 13889-010 Date: May 1, 1989 Subject: Can not change modes (USB, LSB, FM, AM, or CW) Procedure 1. Locate the green wire labeled W148 that goes from one side of the board to the other. Re-crimp the connections on the end of this wire. Bulletin #: 87-002 Date: December 2, 1987 Subject: Improvement of transmitter intermodulation distor- tion figure in the 18 MHz band Procedure 1. Remove the covers from the radio. 2. Replace the following parts on the indicated boards. Current New ICOM Designator Part Board Part P/N C27 10pf Filter Board 12pf 500V 918-01516 C29 47pf Filter Board 12pf 500V 918-01516 Q4 PA Section 2SC2904 906-00434 Q5 PA Section 2SC2904 906-00434 3. Readajust and verify the PA idle current (set to 100 ma) and PA drive current (set to 600 ma) are correct. 4. Replace covers and check all functions. Bulletin #: 5889-001 Date: February 27, 1989 Subject: Some 751As exhibit a slight chirp on CW when operating in SPLIT mode. Information: This modification speeds up the transmitter "start time" circuit on the main board Procedure 1. Remove the top cover from the radio. 2. Remove R32 (currently 180K) and replace it with a 82K 1/8 watt resistor (ICOM P/N 915-01123). 3. Replace the cover and return the radio to service. Bulletin #: 12589-001 Date: April 1, 1989 Subject: Power amplifier oscillates at 1.9 MHz Procedure 1. Remove the top and bottom cover from the radio. 2. Remove the PA Section screws and Remove the PA section from the radio. NOTE: Make sure that the location of each wire going to the PA section is noted so they may be reconnected properly when the PA section is reinstalled. 3. Remove the filter board from the radio. 4. Replace the components listed below on the filter board. Current New ICOM Part Part P/N L2 LR137 LR147 924-02138 L2 LR137 LR147 924-02138 LR35 LR136 924-02206 C1 15pf 18pf Dip Mica C3 2700pf 2200pf Dip Mica 918-01822 C4 220pf 120pf 500V 918-01559 C5 1500pf 1200pf Dip Mica C56 330pf 918-01575 Note: Add this part to the foil side of the board 5. Reinstall the filter board in the radio 6. Reinstall the PA section in the radio. 7. Replace the covers on the radio.