SMD

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Re: SMD

Post by frank1956 on Sat Sep 27, 2014 8:23 pm

WC, Just curious. I have seen it mentions a few time and was just wondering if it was something that happen all at once or over time, and what to be on the look out for as I get more involved in radio's.

Frank
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Re: SMD

Post by Dr. Radio on Sat Sep 27, 2014 9:11 pm

Hi Frank,

There are (2) typical failure modes, one is the "Thunderstorm on a Sunny Day" and the other is the "mysteriously moving radio station", where a strong station suddenly seems like it magically got moved 1000 miles away, the volume in the radio drops drastically and the radio goes all but deaf.

Take the time to read my step-by-step if you haven't already. I go in-depth about IF transformers and their repair.

http://www.tuberadioforum.com/t1915-step-by-step-restoration-ge-t-106c-let-s-go-for-it
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Re: SMD

Post by frank1956 on Wed Oct 15, 2014 5:20 pm

DR. Radio can this type of IF transformer be repaired vice the slug type?



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Re: SMD

Post by 75X11 on Wed Oct 15, 2014 7:48 pm

I believe the SMD occurs in the capacitors that are used in some transformers. The fix would most probably be replacement of the caps. I can't see any in your pics, but someone else may know a secret place.
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Re: SMD

Post by Wildcat445 on Wed Oct 15, 2014 8:28 pm

Frank, I just saw your post. Sorry I did not answer sooner.

As far as I know, any slug-tuned IF transformer can have SMD. There is a silver mica capacitor in the base of the transformer than causes the problem. I have had between miserable and zero luck in repairing SMD. I hate the procedure. My eyes are not good enough, and my fingers not nimble enough to mess with the fine wires. Dr. Radio has the procedure for repair figured out, and his tutorial makes as much sense as any I have seen. Any radios that I have with SMD, exactly two in my entire lifetime, are shelf queens until I find a parts set, or a parts source for replacement IF transformers. I asked awhile back if anybody repops IF transformers, and, if not, why not. I saw your PM about a fix, but that does not sound like something I would fool with, either. My personal feeling on this is that if I can't get the parts to effect a correct and known dependable repair, I will do nothing.

WC

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Re: SMD

Post by frank1956 on Wed Oct 15, 2014 8:35 pm

75X11 wrote:I believe the SMD occurs in the capacitors that are used in some transformers.  The fix would most probably be replacement of the caps.  I can't see any in your pics, but someone else may know a secret place.


75, I believe the caps are located in the top of this IF transformer 2nd picture??
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Re: SMD

Post by frank1956 on Wed Oct 15, 2014 8:42 pm

WC, I know what you mean by eyesight, steady hands etc. That is why I have not attempted it myself yet.

Frank
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Re: SMD

Post by Dr. Radio on Wed Oct 15, 2014 9:26 pm

Hi Frank,

That looks like a RATEL brand transformer. (Radio/Television Products Corp.)

You are correct, the caps are in the top of the assembly. You may have one or more in the bottom end as well, but your pictures didn't include any bottom views (as if you were microscopic looking down at the base of the transformer from the INSIDE.

Regardless, the one you have apart looks horrible. See that dark area on each side on the top? That's tarnish. Those "shapes" used to be bright silver color. Also, pay close attention to that excellent picture you took of the top.....see that little blotch of dark between the two capacitor halves? That's the evil migration right there shorting out the two circuits.

That's why you would be having so many issues with your radio(s).

You'd have to do a little creative mounting there for the traditional dipped mica replacements I used in the GE thread.

I really want to do a very in-depth web page on my work and research involving curing silver mica troubled IF transformer--especially with one of my pioneering processes using modern surface mount technology and post it here as well as ARF.

But who has time??!!!!
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Re: SMD

Post by 75X11 on Wed Oct 15, 2014 9:33 pm

You guys ain't too much older than me and I have to solder components to circuit boards that would be as big as a grain of rice cut into thirds.  You just need the right tools.  And patience.
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Re: SMD

Post by Dr. Radio on Wed Oct 15, 2014 9:46 pm

75X11 wrote:You guys ain't too much older than me and I have to solder components to circuit boards that would be as big as a grain of rice cut into thirds.  You just need the right tools.  And patience.



I can relate. Sort of. I'm 34 and work at a manufacturing/design/engineering firm. We have to do hand repairs on components down to a 0201 footprint level (google it for pictures).

I'm going to try to do as many "giant" (in the electronics world) IF can repairs as I possibly can before my eyesight and hands are kapoot!
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Re: SMD

Post by 75X11 on Wed Oct 15, 2014 9:52 pm

A Luxo Wave magnifier amd a panavise with ency weency pace iron needle tips keep me going with this stuff.
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Re: SMD

Post by 75X11 on Wed Oct 15, 2014 10:01 pm

I did google it. I didn't know the size classifications as we use vendor supplied components. You have bragging rights. But definitely. Very Happy
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Re: SMD

Post by Wildcat445 on Wed Oct 15, 2014 10:29 pm

I may have to make other arrangements sometime in the future. For right now, I will rob IF cans out of parts sets or do without certain radios being fixed. Perhaps some enterprising young man (hint, hint) will start a business of repairing IF transformers for old guys with bad eyesight. It seems to me that by the time I buy all that exotic equipment, I could have paid somebody to just repair SMD for me. When I was your age, 75, I did not even wear glasses, except for reading.

WC

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Re: SMD

Post by 75X11 on Wed Oct 15, 2014 10:39 pm

Here I am, 58 and I'm still getting that when I was your age jazz. Very Happy
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Re: SMD

Post by frank1956 on Thu Oct 16, 2014 1:44 am

DR. Radio the last picture is the bottom view of the IF transformer. There does not seem to be any on the bottom.

Frank
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Re: SMD

Post by frank1956 on Thu Oct 16, 2014 11:02 am

Here is another pic with the mica caps removed from the top portion of the IF Transformer. The one to the left was on the bottom of the one to the right. As I stated earlier I do not see any on the bottom, just these two.

Dr. Radio my question, is since from what I can tell  there are only two, does it mean if I decide to repair this I would have to use two new mica capacitors? i.e. 220pf @500 volts?

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Re: SMD

Post by Wildcat445 on Thu Oct 16, 2014 11:52 am

I am rapidly getting in over my head. Sorry for hijacking your thread, Frank. If you learn how to fix SMD, I will send you some IF cans to fix for me.

WC

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Re: SMD

Post by 75X11 on Thu Oct 16, 2014 12:38 pm

Mica caps would be the types to use, and you are right on matching the original values. The mica caps are generally used for higher frequency applications.
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Re: SMD

Post by Dr. Radio on Fri Oct 17, 2014 8:40 pm

Frank, I hope you took notes or careful pictures of how each mica sheet assembly went together...

You have a fun one there. The 3rd cap adds rebuilding complexity. The 3rd single-by-itself cap shares commonality with one of the main cap legs. Typically this is used to drain any "remnants" of the IF signal to ground to ensure clean audio before the next stage. I'll have to study the schematic on yours, but typically the "IF filter" cap is around 100 pF.

Ideally you would have wanted to disconnect the coil wires but leave the caps alone in place to get a capacitance reading before proceeding with disassembly.

The main two caps look equivalent in size from my screen, so you could assume they are of the same value.

You can take an old wooden clothes pin and modify it to be used as a jig to clamp on the cap substrates and provide electrical connectivity to a capacitance meter. That's a post for another day though...

The bottom line is, it is critical to get the right configuration of connections between caps and coils inside (or as some do, mount caps externally on the legs). Having the exact right cap values is not absolutely critical, but the closer the better for less tweaking.

You want to use silver mica caps (due to their incredible stability and tight tolerance).
Others can argue, but I have always used micas with the 500 volt ratings.
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Re: SMD

Post by frank1956 on Sat Oct 18, 2014 8:52 am

Dr. Radio, I might have bit off more then I can chew on this one, beside the fact that I did not take pictures and jumped way ahead of myself is an understatement.

Frank
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Re: SMD

Post by 75X11 on Sat Oct 18, 2014 10:30 am

If that is the type of damage that causes the smd, and the capacitor is constructed in that manner, If I found damage like that I would gently lift the tabs holding the plates in place to keep them as flat as possible taking pictures of the disassembly to be able to re-orient the plates and tabs and I would try taking the plates and lay them on a flat sheet of bond paper on a flat countertop and use either a very soft toothbrush or a cotton swab or a short bristled acid brush and some 91% isopropyl alcohol and gently scrub the silver surfaces so the excess is flowed onto the paper, then move the plate to another dry flat surface and rinse the silvered surface and underside.  I would then dry the plates with a hair dryer.  I would then swab off the tabs til they were clean and hair dry that area.  I would then reassemble the tabs and plates as they originally were and do it without allowing any skin contact with the plates or tabs.  Rubber gloves and or tweezers would do for this.  In most cases I have found 91% isopropyl alcohol to be a very effective non abrasive tarnish remover and it could be a fix in cases like this. One further thought on this, if this were to be a successful fix, there is a product that is sold as a wrapping paper called VPI that inhibits tarnish and is used to wrap components for long term storage. I wonder if a small square of the paper placed over where the cap is assembled could prevent a reoccurrence of the SMD (tarnish).

I just offer these suggestions as a possible remedy for this sad robber of otherwise functional restorations and the considerable effort that goes into them. I've fortunately not had this happen yet, but this would be my plan of action.
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Re: SMD

Post by neali on Sat Oct 18, 2014 6:32 pm

Dr. Radio wrote:
75X11 wrote:You guys ain't too much older than me and I have to solder components to circuit boards that would be as big as a grain of rice cut into thirds.  You just need the right tools.  And patience.



I can relate. Sort of. I'm 34 and work at a manufacturing/design/engineering firm. We have to do hand repairs on components down to a 0201 footprint level (google it for pictures).

I'm going to try to do as many "giant" (in the electronics world) IF can repairs as I possibly can before my eyesight and hands are kapoot!

So far I have avoided 0201 or 01005 components, but I regularly have to deal with 0402. And I am 54, so you aren't getting any sympathy from me. Very Happy But I have done some IF SMD repairs. Not really that tough but using 100 pF or 120 pF discrete caps, the radio always needs a re-alignment.

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Re: SMD

Post by Ragwire on Sun Oct 19, 2014 11:18 am

Wildcat445 wrote:Frank, I just saw your post.  Sorry I did not answer sooner.

As far as I know, any slug-tuned IF transformer can have SMD.  There is a silver mica capacitor in the base of the transformer than causes the problem.  I have had between miserable and zero luck in repairing SMD.  I hate the procedure.  My eyes are not good enough, and my fingers not nimble enough to mess with the fine wires...WC
I am about there with you on that. I have had some success just breaking the connections to the old internal caps and adding my own externally under the chassis. Far easier than trying to put them in the can. It's still a crap job, but I have gotten it done a few times this way.
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Re: SMD

Post by frank1956 on Sun Oct 19, 2014 11:25 am

Ragwire, I just did one under the chassis, it worked just fine, was able to align my radio with the help of the forum in another thread I posted. Will eventually have to do the other IF transformer. I might try my hand at trying to re-build at least one IF transformer to see if I can do it.

Frank
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Re: SMD

Post by Ragwire on Sun Oct 19, 2014 10:32 pm

I think you can do it. It's just a sucky job you may not want to do twice. Laughing
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Re: SMD

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