What is SMD - Silver Mica Disease? What does it sound like? How do you repair it?

In this video, we look at what SMD is, what it sounds like, and how best to solve the issue. This will be a multipart series on the subject as we look at the electronic theory of how IF transformers work, as well as the actual circuitry of complex Intermediate Frequency Transformers, and the SMD issues that these IF cans can develop. Our radio for this experimentation and reference, is a Zenith 12H092 AM/FM/Phono Floor Console.
There is an introductory video on KZbin of this particular device , which you can watch here for more information on it: • Learn What's Up? with ...
Watch & Learn!
#SMD #SilverMicaDisease #Zenith #Tube #Radio #ElectroRestore

[@hestheMaster]

I will never forget the video that Dan Yahro aka Shango066 put out years ago showing the light flashes from inside the bottom of an IF transformer from silver mica disease. His cure was putting small trimmer capacitors across the removed mica plates and adjusting to get a balanced results. Was a long arduous process to say the least. Eventually replaced with silver mica capacitors which are very stable, precise valued and reliable capacitors. Sadly most manufacturers never do show the capacitance inside the cans in a schematic diagram which would help a great deal there. The primary of the IF transformers are connected to B+ and the secondary to B-, and not ground usually because the metal case is at ground. Good tutorial so far Paul.

[@ElectroRestore]

Yes I loved Shango's video! I had a lot of experience with SMD. However, I never actually seen it arcing like that one was! You are correct, I should have said B- rather than ground. It is held above ground by that resistor on the secondary side. I was more trying to contrast the potential differences between secondary and primary. Dan's video documented just how much potential difference could exist in SDM to actually jump across such a gap. Thanks for your kind words Steven! I appreciate the support you have shown my channel; now and in my earlier days!

[@franzliszt3195]

I saw that too. I really like the extra detail from ElectroRestor.

[@brucebuckeye]

You are a great teacher, sir. Thanks for this video!

[@johnwest7993]

And here I thought it meant Surface Mount Device. Thank you for the video. When I was young and working in a TV/radio repair shop I kept thinking that the crackling sound was from the air-variable cap plates rubbing, but I could seldom ever see any shorting plates. But the sound I heard was the sound your IF can caps made, so now I know.

[@ElectroRestore]

It can be caused by tin whiskers shorting the plates in the tuning condenser. I have actually had to use a strong magnifier glass to find and remove them. In regular variable capacitors, like trimmer caps, however, that does not happen. Because the mica chip is larger than the plates and no whiskers can cut through the mica to shorth them out. Glad you liked the video! Thanks for the comment!

[@izzzzzz6]

good info and well explained.

[@ElectroRestore]

Thank you!

[@stoptheirlies]

You don't want to start with the slugs at centre of the coils, that would be Max inductance you want them to be half way so you can either increase or decrease the inductance.

[@ElectroRestore]

There the center is half way! That was my point.

[@stoptheirlies]

@@ElectroRestore No, the centre is half way down the length of the coil but the centre position is max inductance, with the slug in the centre you have max ferrite between the coils, with the slug at the top or bottom you have min so if you want a position of being able to increase or decrease frequency you need to be between the two.

[@ElectroRestore]

@@stoptheirlies You are correct. The only way to increase or decrease the inductance, is to be either 25% down from the top, or 25% up from the bottom. That would be the center of the range rather than the center of the coil. I am use to tunable capacitors in antique radios and so it really would not matter if you was at max impedance because you tune with the cap values. For slug values (without SMD) I would just adjust for resonance with the slug and not worry about start or stop position.

[@franzliszt3195]

Look forward to the flow-on videos! I see an ohms on the schematic: 0.6 ohms and 9 ohms; what are those? Resistance of the coil or the impedance of the tank?

[@ElectroRestore]

@franzliszt3195, Yes they are the DC resistance of the coil wires. They are low because to DC, the coils are like just any other wires, only much longer. So they have some resistance. The IF transformer makers included them to their customers, because the anticipated failure would be an open or a short in the coils themselves. Measuring the resistance (DC ohms) should be in that ballpark. They did not supply the capacitance in most cases because they did not foresee any real chance of failure there. Great question! Thanks for asking! I will be uploading another video in this series soon; hopefully in a day or two!

[@franzliszt3195]

@@ElectroRestore thank you for the response. It is seldom that anyone makes what may be called a ‘definitive’ version on a subject. Most only go very a partial answer.