Sadness = Silver Mica Disease (SMD)

Post by **Sherman** » Mon Oct 16, 2023 6:58 pm

Sadness is discovering your radio has silver mica disease.

Post by **Baltasar** » Mon Oct 16, 2023 6:59 pm

Bite the bullet, Sherman.

Post by **Sherman** » Mon Oct 16, 2023 7:00 pm

Rebuild 6 IF cans?

Post by **Baltasar** » Mon Oct 16, 2023 7:01 pm

Clever boy. Life is full of disappointments. Do what you have to do.

Post by **Sherman** » Mon Oct 16, 2023 7:02 pm

OK, Mr Balti.

Post by **Bullwinkle** » Thu Oct 19, 2023 6:23 am

Do them one at a time, maybe one per week to make it not such an overwhelming task. Start from the RF end and work your way towards the audio. If you are a good boy you might get lucky and cure it on the first one you do. Or not. Get 'er done, my stable needs cleaning too.

Post by **Sherman** » Thu Oct 19, 2023 12:19 pm

I did the first one, the front-end FM IF can. Radio still works and I thought I was gonna get lucky but it started thunderstorming again after 5 hours. So now I'm gonna do the front end AM IF can. Note that these two IF cans have windings in series, so if one is bad it will affect both FM and AM. I knew from the signal tracer that one or both of these two was a problem. There may be more downstream too.

Post by **Baltasar** » Thu Oct 19, 2023 12:58 pm

Par for the course. Keep going!

Post by **Curly** » Thu Oct 19, 2023 9:45 pm

polishing the silver
until one day your like where is the silver
she be gone

Post by **Sherman** » Sat Oct 21, 2023 11:46 am

For sure. Started on the 2nd IF can (AM front end). Got the wafer removed and re-installed the can with just the coils. Then I measured the wafer capacitors to the best of my ability. Then I ordered equivalent mica caps from Digi-Key. So a week to do each can is forced by having to measure and order the caps. You have to cleanly remove the wafer intact so you can measure the caps. And you have to remove SMD with an eraser and blade before you measure. Of course we're going to have to re-align the rebuilt IF can slugs (per manufacturer instructions) after she be gone.

new_guy · Post by **new_guy** » Wed Oct 25, 2023 6:06 pm

Hey Sherm, what's going on with T1A? No progress?

Post by **Sherman** » Wed Oct 25, 2023 6:07 pm

French toast Digi-Key shipping is like molasses. Never forget, patience is a virtue.

Curly asked me what is the point of virtuousness. Do you know?

I'm pretty sure Frankaboy knows the answer.

Post by **Albert** » Wed Oct 25, 2023 6:41 pm

It's simple.

https://fs.blog/tit-for-tat/

Get serious.

Post by **Sherman** » Thu Oct 26, 2023 3:56 pm

Makes sense, thank you Albert.

Guys, the caps arrived and I completed the T1A AM front-end can. Everything still works so I have to wait 5 hours to see if it starts thunderstorming again. If so, we move on to T2.

One interesting thing is that one of the resistors associated with T1A was 350 ohms when it should have been 220. That is way out so I replaced it. We're supposed to have 5% tolerance. It coulda been noisy too as it was carbon comp. Keep your fingers crossed.

And guys I can't say too much right now but there is something very exciting going on here in DG land. Stand by!

Post by **Rocky** » Thu Oct 26, 2023 3:58 pm

Shhhhhh!

Post by **Sherman** » Fri Oct 27, 2023 11:09 am

I completed T1A and it improved things but it's still not fully fixed. Now, instead of the crashing thunder I get just a little hiss and occasional pop after several hours. I tackled T2 this morning and luckily had the needed micas on hand. Finished up T2 and the radio still works. Waiting now to see if it goes bonkers after a couple hours.

new_guy · Post by **new_guy** » Fri Oct 27, 2023 11:10 am

Your persistence is admirable.
:bravo:

Post by **Sherman** » Fri Oct 27, 2023 6:26 pm

Things are looking good. No hisses or pops so far after T2. Maybe we should do T3, T3A, and T4 just for futureproofing. This thing can outlive all of us.

My notes to share because I care: It's not so much about silver migration as it is about deterioration of the interfaces between the mica wafer silver surfaces and the contact pads. Mechanical motion, thermal heating/cooling, vibration, and environmental exposures corrode and abrade the interface, deteriorating the pad-silver electrical connection.

Post by **Curly** » Fri Oct 27, 2023 6:31 pm

Albert wrote: ↑
Wed Oct 25, 2023 6:41 pm
tit-for-tat

if my girl had tats on her tits it wud be over

Britney · Post by **Britney** » Fri Oct 27, 2023 6:42 pm

That's what I was thinking.

Post by **Sherman** » Sat Oct 28, 2023 11:47 am

It ran all night with no issues. I'm gonna hold off on doing any more cans. A person that knows much more than me told me that aligning the FM limiter/discriminator is tricky. The FM IF cans I re-built can be re-aligned very easily but you get into a can of worms when you mess with the limiter/discriminator. We'll cross that bridge if we ever get to it. I'm gonna re-align the IF cans I touched today. Actually AM sounds fine as is, but FM is a bit off.

Wonder Woman · Post by **Wonder Woman** » Sat Oct 28, 2023 11:52 am

Britney · Post by **Britney** » Sat Oct 28, 2023 12:01 pm

Poor worm!

Worms are people too.

Post by **Sherman** » Sun Oct 29, 2023 10:26 am

Q: What did the maggot do at the baseball game?
A: Wormed the bench.

So guys, I went ahead and did T3, the 3rd FM IF can. Radio sounds better on FM but I still need to do full alignment. I'm probably not going to bother with T3A, the 3rd AM IF can, because AM sounds fine and I plan to use this for FM playing.

Here is a photo of the wafers showing how they look. Sorry about the focus, my phone sucks. The one on the left is T2. It was cleaned with an eraser to remove most of the black tarnish. But you can see the degradation where the metal pads were contacting. The one on the right is T3. Just total crapzilla.

new_guy · Post by **new_guy** » Sun Oct 29, 2023 10:32 am

OMG, what were those Zenith engineers thinking when they designed this stuff?