silver mica disease

so-tingly wrote:

Turns out it wasn't SMD after all. 
Bad antenna connection and the cap I mentioned cleared it right up.
Thanks again and sorry for all the confusion with the correct meaning of SMD.

YOU KNOW EVEN THOUGH IT WAS SOMETHING DIFFERENT, your trouble shooting will help others to search for the same thing on their Radio repairs.

Thanks for posting your findings

Turns out it wasn't SMD after all. 
Bad antenna connection and the cap I mentioned cleared it right up.
Thanks again and sorry for all the confusion with the correct meaning of SMD.

Cliff, In every IFT I have ever seen with SMD, the capacitor in question is buried in the plastic of the base of the IFT. The solutions are to replace the IFT or cut out the base, removing the capacitor and replacing it with one of the appx. correct value, then realign the IF strip.
An eraser is a great idea,  , but not possible to use because the caps are cast in the base of the IFT.

Having worked with military circuits and cards to repair. This issue is also present and disables the equipment. You can look for bad components to no avail. Whats one thing to further look for is Silver Migration. 

Moisture is a big culprit. Also salt air. So most all circuit cards are conformal coated for those reasons. If you look at a card and holding it so a bright light shine through the back or front of the card you will see the migration as being very hard to  find as a lot of times it's Transparent. But it blocks some light from getting through, so you look for an area that is not the same uniform card color. In some cases it will show itself in a shadow tint of grey.


It’s caused by electrolysis between traces because the voltage polarity or in some cases, but mostly just a difference in voltages.
This is where you would use an eraser across the trace migration then repair the trace itself and if there is any corrosion that ate away the trace.  

Theres a lot more to this than I am willing to type in to continue     .

FrankB wrote:

We know what is being discussed.

In truth the word Migration is more accurate.

This site is peer reviewed.

I have always heard it referred to as Silver Mica Disease, not Silver Migration Disease.  Same thing. Potato Potatoe.
We know what is being discussed.

In truth the word Migration is more accurate.

so-tingly wrote:

Sorry if the title may be misleading but when looking it up, that's what most videos on Youtube refer it as.

YouTube is one of the few sites which I can think of which are less accurate than Wikipedia. Lack of accuracy is typical of sites which are not peer reviewed.

The title of this topic is incorrect. SMD is not silver mica disease - it is silver migration disease.

Well... I think I solved the problem. 
Come to find out it may not be SMD. I compared the suspect radio with a radio that has the larger IF cans. It got the same staticky hissing sound as the other.
I also added a .015uf cap to the antenna, even though the schematic shows none. The stations came in much more clear and the static was very low.
I think the weather and time of day were the culprits this time. Rainy, overcast and just plain old nasty weather.
Thanks for the help.

SM disease is a real PITA. The symptoms you describe are typical of it. If it is really SMD, the noise will continue to become worse and then no reception at all. At least that is what every one of the radios I had with SMD displayed as symptoms.

There are only 2 cures I am aware of:

 Replace the IFT's

Cut out the cap in the base of the IFT and either replace it with an epoxy silver mica cap,  or a surface mount cap if you can find one that will handle the voltage.

Outside interference can cause noise similar to SMD. Time of day, weather, etc. can easily make reception noisy. Hissing between stations is common, depending on the design of the set.
 Also these "new fangled so called energy saving" ballasts in lamps, SMPS in TV's and computers can really cause mass noise. Also alarm systems, fish tank thermostats, power pole insulators breaking down, ad infinitum. 

(SMD is one reason I offed my entire Hallicrafters collection, because every one of them had it).

Turning your radio in a different direction WILL change reception, as many of the radios have a built in antenna, and moving the radio has an effect on the directivity of the antenna.

HTH
Frank

I'm was playing a radio I long since repaired. A Silvertone 528
Within 2 days the stations have been coming in weak and there's constant static that sounds like frying eggs without the intermittent pop.
I've heard SMD before and I don't think it sounds like static with an intermittent pop or sudden loud crackling.
Sometimes a station will come in nice and clear but this static hissing sound happens between stations.
I'm also wondering if time of day or weather has something to do with it.
Also when I turn the radio in different directions the stations come in a bit more clear. I understand that's what happens with these old radios.
I've rebuilt IF cans before but its such a pain in the a--
Thanks for anything anyone has to offer.