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IC28A.7
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1990-10-14
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Model: IC-28A
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 #: 28Oct86-012
Date: October 28, 1986
Subject: Improve RX sensitivity 1 dB
Procedure
1. Replace the following parts on the receiver board:
Current Part New
Part Identifier Part
18pf 50V C21 12pf 50V
8pf C23 9 pf 50V
39pf C108 56pf 50V
Jumper W5 Remove
Model: IC-28H
Bulletin #: 28Oct86-014
Date: October 28, 1986
Subject: Improve RF output power
Procedure
1. Add R113 between IC-6 pin 1 and ground on the main board.
2. Remove and replace the following parts on the main board:
Current Component New
Part Identifier Part
LA-233 L22 LA-235
12pf 50V C46 47pf 50V
33pf 50V C52 22pf 50V
22pf 50V C109 10pf 50V
Model: IC-28A/H
Bulletin #: 28Oct86-015
Date: October 28, 1986
Subject: Improve S-meter gain
Procedure
1. Remove and replace the following parts on the RX board:
Current Component New
Part Identifier Part
33K R37 27K
1.5K R45 2.7K
47pf C62 100pf
This modification will increase the S-meter gain by 5dB
Model: IC-28A/H
Bulletin #: 3Nov86-003
Date: November 3, 1986
Subject: Prevent birdies at 154.755 and 154.810 MHz
Procedure
1. Cut the land between Pin 1 of IC-1 (MV87001-G) and R102 on
the main board.
2. Install a 1 MicroHenry coil (1R0) between Pin 1 of IC-1 and
R102 on the main board.
3. Install a .01 uf capacitor between Pin 1 of IC-1 and ground.
4. Cut the land between Pin 5 of IC-1 and C27.
5. Install a 1 Meg resistor between pin 5 of IC-1 and C27.