Author Topic: Icom 745 missing upper bands (Read 7659 times)

KC4UMO · « **on:** February 28, 2008, 05:39:28 AM »

I went out in the shack yesterday evening after a two week absence. (sick and busy). Fired up my 745 and noticed that from 24 to 29 mhz was not working. flipped through the bands and went back and saw they were working. after a few minutes of playing around I found it to be intermittent.

The original owner never used those bands. He used mostly 40 and 80 meters CW. After looking through the service manual there is one relay that controls that segment of bands. In the matching network of the final stage.

When the problem occurs the s-meter falls to zero and sounds as if the antenna has been disconnected. All functions still work but no rf power out.

So appears I have to replay a dirty relay.

WV6Z · « **Reply #1 on:** February 28, 2008, 04:38:33 PM »

Buddy is it a \'permanently\' sealed relay or can you pop off the top and clean it up to be sure it\'s not a capacitor issue?

KC4UMO · « **Reply #2 on:** February 28, 2008, 05:08:22 PM »

Hi Tom,
Really this is just an assumption and may not be accurate. Another cause may be a cold solder joint.Really do not think it is a electronic componet due to the fact that it is intermitted. You can go through the band switch and here all the relays "click". 24 to 29 mhz is on the same band relay. According to print.

These are the little minature relays (sealed). So no chance of taking apart to clean.
I thinking that maybe the relay has become heavely tarnished due to the lack of use on those bands.

Thoughts?

WV6Z · « **Reply #3 on:** February 28, 2008, 08:31:49 PM »

Agreed, it sounds like you are on the right path to me Buddy...... keep us posted!

KC4UMO · « **Reply #4 on:** February 28, 2008, 08:57:26 PM »

May be late saturday before I get the chance to look at it. Have to work tommorow at straight time. They off set our work week this week due to rearanging the line I monitor. I have a few jobs on the side I need to work on saturday.

I will let you know how it goes though.

N4KMC · « **Reply #5 on:** June 07, 2010, 10:20:14 PM »

I have just purchased a 745 and it is doing the same thing on the 24 and 28 Mhz bands, I was wondering what you may have found out on this rig problem.

Thanks, John