The dreaded "Silver Mica Disease"
Posts: 825
Threads: 113
Joined: Aug 2012
City: The Villages
State, Province, Country: Florida
Hello everyone,
Well, I think I have it. I'm working on a Zenith 7H822 AM/FM radio. I've done the tubes, caps and resistors. When I first turn it on I get a crackling that sounds like lightning on AM only. After a few minutes it goes away. Does it sound like I have it?
If so, how do I determine which IF can has the bad one? I saw a thread on this phorum a while ago that shows how to replace them, but I guess I could just replace the can (I have some spares). I just need a way to locate the bad one.
Thanks.
http://www.nostalgiaair.org/Resources/309/M0025309.htm
Eric
The Villages, FL
Member: Philco Phorum, ARF, ARCI & Radiomuseum.org
Posts: 157
Threads: 7
Joined: Feb 2013
City: Osceola, IN
Sounds like you have it Eric. To test I believe you can put a voltmeter on the secondary of the transformer. If you get a 0 or low negative reading you are OK. If you get a positive voltage reading you've found your culprit.
Posts: 214
Threads: 16
Joined: May 2010
City: Kokomo, IN
I have a Zenith AM/FM radio that has the same problem if that is what it is maybe I will fix mine to.
(This post was last modified: 01-15-2014, 11:37 AM by vinzer.)
Posts: 825
Threads: 113
Joined: Aug 2012
City: The Villages
State, Province, Country: Florida
Thanks, Jontz. I'll check it out. I'll let you know how it turns out.
Eric
The Villages, FL
Member: Philco Phorum, ARF, ARCI & Radiomuseum.org
Posts: 157
Threads: 7
Joined: Feb 2013
City: Osceola, IN
Vinzer, I love your updated location! As a Northerner who heads South of Indy semi-frequently I won't miss driving through town on the old "bypass".
Posts: 16,220
Threads: 562
Joined: Oct 2011
City: Jackson
State, Province, Country: NJ
Eric
This disease is only cured by shots. In the backside. Once a day, early in the morning. Until you stop hearing scratching sound.
Posts: 825
Threads: 113
Joined: Aug 2012
City: The Villages
State, Province, Country: Florida
Thanks Morzh, I think I can learn to live with it. Kind of like a bad back. 
Eric
The Villages, FL
Member: Philco Phorum, ARF, ARCI & Radiomuseum.org
Posts: 1,106
Threads: 88
Joined: Jun 2011
City: Tacoma
State, Province, Country: Washington
If you have one bad can, good idea to replace the caps in both, since if it isn't already, the other one will go soon.
Posts: 825
Threads: 113
Joined: Aug 2012
City: The Villages
State, Province, Country: Florida
Thanks Brenda, I thought about that.
Eric
The Villages, FL
Member: Philco Phorum, ARF, ARCI & Radiomuseum.org
Posts: 4,804
Threads: 54
Joined: Sep 2008
City: Sandwick, BC, CA
It could also be a dirty tube socket, especially in a set using loctals or miniature seven pin tubes.
Regards
Arran
Posts: 825
Threads: 113
Joined: Aug 2012
City: The Villages
State, Province, Country: Florida
I found the problem!  First of all I have to tell you that I'm working on more than one radio right now and the problem was with an Airline AM/FM Model# 15BR-1535B not a Zenith. It was pretty simple really, once I found it. There was one of those black capacitors, a .02mf, with 5 color bands on it that connects across the a/c line. I thought that it was the kind that doesn't have to be replaced...WRONG!
The more I do, the more I learn.
Thanks everyone for your help. Maybe what I learned can help someone.
Eric
The Villages, FL
Member: Philco Phorum, ARF, ARCI & Radiomuseum.org
Posts: 1,106
Threads: 88
Joined: Jun 2011
City: Tacoma
State, Province, Country: Washington
Posts: 157
Threads: 7
Joined: Feb 2013
City: Osceola, IN
Glad you found it Eric! It presented almost exactly like silver mica, but just goes to show how hard it is to tell what's wrong when you are working on a radio, let alone just guessing from the internet. Congrats!
(This post was last modified: 01-16-2014, 07:35 AM by jontz.)
Posts: 16,220
Threads: 562
Joined: Oct 2011
City: Jackson
State, Province, Country: NJ
Eric
Let me get it...you DID NOT replace all capacitors? Big mistake if this is the case.
Another thing is, of all things this very capacitor HAS to be taken out and replaced with X-grade capacitor (line filter).
And, if it is before the power switch on the Mains' side (as is often the case) - place a 200K resistor across.
Posts: 825
Threads: 113
Joined: Aug 2012
City: The Villages
State, Province, Country: Florida
Wow Morzh, ease up!  As I stated, I thought this was the type that "didn't go bad". Like the mica caps. Anyway, like I said, "The more I do, the more I learn".
I believe in learning by my mistakes.
Eric
The Villages, FL
Member: Philco Phorum, ARF, ARCI & Radiomuseum.org
Users browsing this thread: 10 Guest(s)
|
|
Recent Posts
|
|
6TPZ and 5TPO Radio Help
|
| 1 - 0v - correct
2 - 0v - correct
3 - 0v - --------------------- both 3 and 4 should be the same. Check L2 for being ope...morzh — 05:15 PM |
|
B&K 1077B no video
|
| I'm going to get back into it tonight. but I disconnected the 2 main resistors off this supply going to different parts ...TV MAN — 04:04 PM |
|
6TPZ and 5TPO Radio Help
|
| Sorry. The test points are as follows:
1 - 0v
2 - 0v
3 - 0v
4 - 12v
5 - 0v
6 - 11.9v
7 - 12v
8 - 12v
9 - 12v...R3Sons — 02:09 PM |
|
6TPZ and 5TPO Radio Help
|
| OK, so 18 and 19 as they should be.
What is "everything else?"
Try to be more specific in your descriptions:...morzh — 12:44 PM |
|
6TPZ and 5TPO Radio Help
|
| Yeah, I'm still on 5TPO. Sorry, my bad, points 1 and 2 should be points 18 and 19 (easy mistake :think: ) X7 is shown ...R3Sons — 11:42 AM |
|
Philco 40-120C Filament Wiring
|
| Hi folks, I'm in the process of restoring a Philco 40-120C and I'm finding the wiring to be a bit puzzling. According to...bluecap — 11:28 AM |
|
462ron
|
| Hi Levi, here’s just a thought. Most radios run the oscillator higher than the dial setting. Say you set your radio to 1...462ron — 10:10 AM |
|
1930s Stewart-Warner Tombstone Radio need help identifying model number
|
| Another Update: I found a couple of damaged coils inside this radio that might have something to do with why this radio ...captainclock1988 — 10:51 PM |
|
6TPZ and 5TPO Radio Help
|
| If you are still on 5TPO, you lost me there. What X7? What Points 1 and 2?morzh — 08:37 PM |
|
6TPZ and 5TPO Radio Help
|
| Quick progress report:
X7 is broken. Only one leg soldered, the other missing and the diode is cracked.
I've replaced...R3Sons — 05:05 PM |
|
Who's Online
|
There are currently 5510 online users. [Complete List]
» 2 Member(s) | 5508 Guest(s)
|
|
|
|
 
|
![[-]](https://philcoradio.com/phorum/images/bootbb/collapse.png "[-]")
