[ICOM] IC-781 Gurus IT's ALIVE !!!

[Gary P. Fiber]

On 3/12/2012 9:24 PM, Mike Olbrisch wrote:
> UPDATE to the story of my IC-781 burning up while I was away at the dog
> show.
>
> About 2 weeks ago my some came over.  Since I hurt my back and couldn't get
> behind the desk to remove the IC-781, he did.  A few days ago I thought
> "Ahhh - what the heck".  I plugged it in, turned my head away to protect my
> eyes, and punched the power button.  IT CAME ON !!!  It seems the surge
> protector was what blew!
>
> So now that my back is all better, and I have the radio on the bench, I want
> to give it a good going over before putting it back in service.  It had
> developed a few problems, mostly due to lack of use I think.  Maybe some of
> you 781 GURUs can add a few things to check while I have it open.
>
> ADAM?  GARY?
>
> Here is what I have.
>
>
> #1.  RX is sometimes intermittent.  Tap the mic button, or turn the preamp
> or attenuator off/on and it works for a while.  Let it run a few days and it
> is fine.  The problem is ???
I would suspect a T/R or preamp relay has a bad contact. I don't have a 
print here but following the antenna into the receiver should show whats 
inline and likely lead you to the trouble.
> On humid days when I turn it on for the first few minutes (until it heats
> up) I hear an intermittent arching, I suppose it is coming from the HV CRT.
> This only happens on humid days.  The problem is ???
Can you identify the area the arcing is coming from? Might be the power 
supply though the CRT is more likely due to the higher voltage.
At Icom we replaced the entire CRT unit when defective. You might remove 
the top of the CRT unit and look around for arc tracks.
You can pretty easily remove the CRT unit and look at the circuit board 
both top and bottom once its case is removed.

 >>Many/most of the controls are dirty/noisy. I have a can of the 
"original" blue shower. the one that doesn't damage plastic. I also have 
DeoxIT D5 spray, and DeoxIT GN5 (formerly pro-gold) spray. Any 
suggestions? (I think the D5 is best for controls.) Anything else I 
might want to look at. I trust you guys forgot more than I know about 
it. I want to do this and get it right so the next 5 years or so are 
nothing but FUN! <<

I like the DeoxIT products other than replacing those controls I'd give 
them a spray. I once counted the front panel controls , buttons and 
there are 117 of them to deal with. If you remove the front face plate 
be careful when replacing it as it happened more than once a control got 
broken as it was not through the panel.

At Icom there was also some service of the power supply, changing out 
caps, etc.

Gary K8IZ




-- 
Gary Fiber K8IZ
GROL PG-19-6691 with shipboard radar endorsement
Washington State resident