icom 2800 gain problem

[matt s]

Knowing there are a bunch a hams here I thought I would see if anyone knows a fix for this.

The gain (volume) knob on the vhf side of my 2800 is no longer functioning. It appears to be a type of resistor and the resistor part is blown out leaving the vhf side to only have one volume level (LOUD!).

I did take the head unit apart thinking that the knob itself was the culprit but the knob is integral into what appears to be a rheostat type resistor on the circuit board.

So the question is how hard is this going to be to fix? Can I even find the right parts for a discontinued radio like this?

Thanks in advance.

(I will try to take a photo or two of the inside)

 

[matt s]

Here is a shot of the knob in question. It's soldered on to the board in several places.

 

[gary in ohio]

Your going to need to call Icom and find out if you can even buy the part. If your comfortable with a soldering iron then replacement shouldn't be that hard

 

[matt s]

thanks Gary, that's pretty much the conclusion I came to after taking it apart a little further. Looks to be soldered in 5 spots, would just need the part. That may be difficult as the radio was discontinued some time ago.

 

[matt s]

Called Icom and they are shipping the part. $2.

Now to find someone with better soldering skills than me!

 

[Tennmogger]

For 2 bucks you can't go wrong. However, from your description of the failure (loud volume all the time) the problem is probably loss of connection to ground on the low side of the potentiometer. The pot acts as a voltage divider. It works like this: the high level audio comes in to one end of the resistor. The other end of the resistor goes to ground. The wiper (moved by the knob) adjusts the wiper between the (electrically) 'upper' end of the resistor and the lower (ground) end. The wiper therefore changes level from 'high' signal to 'low' signal. If the ground end gets a bad solder joint from movement of the pot, the voltage divider no longer functions (because there's no "low') and you get high volume and little adjustment. There will be a little volume adjustment because the pot is still in series with the signal path, but there's no ground to allow pulling the signal to 'off'.

Touching a soldering iron to each of those connection points might fix the problem. Use a touch of fresh solder (with flux) to enhance flow. Note that several of the connection points are just mechanical mounting points and might take a little extra heat/time, but those might be loose too, probably the original cause of the failure.

Bob WB4ETT

 

[Mash5]

Most pots have very low reliability (at least by automotive standards). If you have the right part just swap it. With the part in hand and the radio apart it's a 5 min job with the right tools. I have found that 3/4 of being "good at soldering" is having a good iron. Find a local HAM and fix it right. Up there in Alaska I would think you would want to get it right before heading out in the bush. Heck if it were my rig and the parts were $2 I would do all three just for good measure.

 

[matt s]

Thanks all. Tempting as it is to try to touch up the ground soldering, I am going to have a local electronics shop put in the new pot. It's worth the extra few bucks to have it done well. Now I just need to find the time to drop the dang thing off for the repair.

 

[xtatik]

i have found that 3/4 of being "good at soldering" is having a good iron.

fact!