ICOM IC-718 PA Transistor Replacement

I don’t know how common it is for the finals to go soft in the ICOM IC-718 Transceiver, but in my case they had. It had been purchased used in 2009 and had been back and forth through another owner sometime in between then and now. Early on it had a electric shock problem that disabled the PLL board and this was serviced at a ICOM repair depot. Since then, it has been in my possession as a receiver. Output had been no more than 25 watts key down. I picked up from the web, the ICOM IC-718 service manual and took a number of weeks going over it. I also looked at the process in removing the PA board from the radio. The removal was easily done, photographs are needed before taking things apart.

Cooked output transistors

The 2N2904’s look quite black on the edges. Next was to desolder the transistor leads and lift them from the board.

2n2904’s removed

The transistor landing pads were cleaned up and the crud removed. Lead pads looked in very good condition. And were ready for installation of the new 2n2904 transistors.

First transistor in place

The board is placed back into the radio and fastened down. The new transistor is placed in its location and lightly attached in place so as not to move around. The orientation is double checked before making a solder task. The transistor is then soldered lead by lead, until cooled. The go easy on the heat, with each transistor connected to the heat sink chassis to take away excess heat but be careful regardless.

New Pills

Complete the procedure with the second 2n2904 and return the protector resistor and diode to their protection locations. If you have some heat transfer goop handy use it.

Attach all remaining screws, feed lines, power plugs in the chassis.

Power on the radio and check for normal receiving qualities that things did not change during the installation of the PA board. In my case, all was well. Align as the manual describes in the transmitter section. In my case all was well other than a minor adjustment of idle current, and a slight case of high drive on the PA. Test in stages, with 10 watts at a time into the dummy load and observe power output on the watt meter. Look for expected results and swr levels and check for heat on the transistor that they feel normal to a brisk touch test. In my case, I heat was low, and they appeared to be working fine. Power levels came up normally as test power was advanced. I keep key down very short.

In SSB, my signal looked good and carrier suppression was working good. I could pick up my audio, at 5 watts on the dummy load, so in my SDR receiver band scope the image looked good.

I attached the DX-88 antenna and set the output to 50 watts and answered a CQ from South Florida. The reception report was delivered as 57 and audio was of normal quality. I described my operating condition and signed off.

Well I was quite pleased. I did a minor power check key down at a power setting of H or 100 and all looked good on the watt meter. I closed up the lids and considered the bench test procedure completed.
This task is not for the faint of heart, but was straight forward. Make sure you have new parts on hand first, and look at all the schematics in the PA Board long ahead of time. Lifting transistors like this must be done with the board out and a good desolder tool on hand. I am not a fan of solder wick, as heat climbs quickly with it when one lingers and this just cooks traces and solder pads. The the pump desolder tool is cool and fast as soon as the solder has time to flow you hit the sucker and move off. Makes a nice clean lift, even if you have to pass a couple of times on the old transistor lead metal.

You can do it but you have to be ready to go slow and take your time. It is always a good thing to practice on a old PA of some sort if you can before hand.

Cheers

Shoeless Bruce VE4BDF

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