ICOM IC-7800 PA UNIT MODULE USED-NEED NEW PA TRANSISTORS
This procedure requires significant disassembly of the radio, and careful handling of the various parts. You will require a work area approximately twice the footprint of the radio, as it has to be rolled onto its ends and also inverted at various times. Have several small plastic bags or containers to segregate the screws that you will be removing, so they can be returned to their correct areas within the radio.
- Remove both the top and bottom covers and place them aside where they will not fall or be scratched. On the bottom of the radio is a small fan. Once the bottom cover is removed, you will need to have at least one spacer under the radio, to prevent the whole weight of the radio coming to bear on this small fan.
- Remove the rear panel. Numerous screws hold this panel on, so keep them segregated from the rest of the screws you will remove. One screw, below and between the two RCA Connectors, is a self-tapper (sheet-metal screw)…make sure it goes back into this hole, and no other! The screws each side of the antenna connectors also come out, and once you have done this, the assembly that holds the antenna connectors will be free to hang on its cables. Remove the rear panel and place it aside. Now, carefully remove the ribbon cable from the connector on the antenna connector assembly. This is not imperative; however, if you decide to leave it connected, make sure that it is not supporting the weight of the board it is plugged into, or twisted in any way.
- Four of the screws that you removed from the rear panel held the rear of the PA Module in position, so you are already half way to removing this module. Now, go to the front of the Antenna Tuner Module. You will see two small electric motors, one above the other. If you look down below them, you will see two cast feet that hold the front of the Tuner Module to the radio. Remove the two screws ( If you have , or can make, a magnetised screwdriver with a longish shaft, this makes life much easier, so you can undo, and withdraw the screws ) and place them with the screws you are about to remove from the side panel of the radio on the RHS, right next to the Tuner Module. Remove all the screws from the radio side panel, and remove the panel, placing it out of harmï¿½s way. You will now be able to carefully remove the Tuner, outwards, away from the radio. There are three coax connections, and two control cables that you can carefully unplug, and a large ribbon cable on the top of the Tuner…as you carefully move the Tuner from the radio…go slow here…you will see all the cables that are plugged into it…remove them one by one. They go back in easily, and cannot be mixed up, due to length and connector type. If you have a Digital Camera, take pictures…lots…if you are at all worried about where things go.
- This applies to the whole procedure actually…as you can take a break, and know that the pictures you took will reveal where things normally go, should you get interrupted or have a memory lapse.
- Remove the Speaker Box, and place it on top of the Power Supply. There are four screws holding it in, two at each end that are quite obvious. Unplug the Fan Supply cable from the front LHS of the radio…it is a small white connector with Red/Black cabling that snakes down to the fan. Unwind it from the loom and see that it is free, so you can remove the PA Module after the rest of the procedure is carried out. If you now look into where the Tuner Module was located, you can see the PA Module, and there is now plenty of room to allow you to remove it…we are almost done here…you will see next to the end of the fan closest to the Tuner Module, two self-tapper screws that hold that side of the PA Module in place. Remove them.
- Now, go to the other end of the fan, and you will see another two screws…one down low and the other on a step in the mounting bracket, that is attached to the Power Supply Module. This screw is a metal thread, not a self-tapperï¿½make note of this. Remove these two screws. The PA is now free of the radio, and the only thing preventing its removal are 5 cables….two are RF and unplug easily…the PA Output cable at the fan end of the Module, and the PA Input cable, at the rear. The other cables are control and DC Cables…one cable down near where the RF Input cable is, the other next to the DC Input cables. They both unplug…gently wiggle them out. Now, you will need a screwdriver to remove the DC Supply Cables.