Anyone ever successfully repair a blown yoke?

[YellowDog]

I haven't tried a yoke, but I did fix a transformer once. There were 4 or 6 strands broken so I used continuity to determine which was the outermost pair and then determined which of the remaining strands were connected. I then bridged from one of the outer pairs to one of the other pairs to the remaining pair to the last of the outermost pair. I used heatshrink tubing and then just left them out rather then risk damaging the enamel by tucking them back in. It looked fugly but the transformer worked when I was done. This sounds very similar except that the transformer is a yoke.

There was also a web site I bumped into (and of course can't remember where now) that detailed how somebody remanufactured a yoke by rewiring it from scratch. That might be overkill, but if you can find that site you might get some tips.

Here is a site that talks about using a ring tester on coils like transformers and yokes: http://www.articlealley.com/article_11526_45.html

And from our own JROK: http://www.jrok.com/xfer/xystuff/

Good luck.

ken

 

[KevinMullins]

What about fingernail polish?

Maybe.
That is kinda along the lines of what I was thinking .... something that would easily brush on and cure hard to coat the wire. (maybe the fingernail clearcoat strengthener stuff of sorts)
A yoke shouldn't get hot enough to bother it.....

 

[modessitt]

Well, I connected the strands that had continuity to a terminal, and my ring tester said it was good to go. My meter read 40.3 ohms instead of the 44.1 of the original. Hooked it up and I get this:

The bottom edge is parallel to the tube edge, so the yoke isn't crooked. The chassis hasn't been rebuilt yet, but the geometry isn't perfect. Of course, it's better than what it was....

 

[mecha]

got those metal wedges on there? shouldn't that help the corners out?

PS: this is amazing. lol

 

[modessitt]

I pulled the 5501 yoke off and put the 5515 yoke on in the same position. Rings in the same position.

After leaving it on for while the bottom curved up and looped back towards the top, like a piece of paper that curled up at the bottom...

 

[slots]

Could you use something like this on the repair.
http://www.kpg-industrial.com/products/insulating_varnish/

 

[hindered]

Subscribed.

 

[cadillacman]

mod actually fixed a yoke. Needs some tweaking but he actually did it. Effing amazing!

 

[modessitt]

I don't know if I can fix it completely. Some of the busted strands are way up under the edging of the plastic around the yoke, and it's all glued or epoxied in place, and i don't think I'll be able to get to them in order to try to connect them all. Apparently it doesn't like not having those strands connected, or perhaps my quick fix needs to be improved a bit....

 

[modessitt]

Let's bring this thread alive again, shall we? Updates coming in 2 or 3 new posts. If you're interested in this topic, pay attention now.

When we last left you, I had found a couple of the fried strands that had continuity to each lug, connected them, and got this result:

Well, I wasn't happy with this result, even though I now had vertical deflection. The distortion was too much for any self-respecting arcade hobbyist to live with - even for a medium-res monitor. Plus, after it was left on for 30 minutes, the distortion got worse and the image started to fold back on itself.

I had no luck finding another yoke to buy, but I did find someone who had a spare they let me borrow, so at least I could do chassis repair. Unfortunately, this person wanted to keep it as a spare and would not sell it. My customer still needed a yoke.

So, tonight I sat down and decided to see if I could fix it "better"....

 

[modessitt]

Okay, the first thing I did was disconnect the two strands I connected before. I was able to pull part of the standoff frame away from the copper wiring by cutting into the glue that held it in place. This gave me access to some of the very short strands that were right under the edge there.

Next, I grabbed a pencil Exacto knife and a flat-head screwdriver. I stuck the flathead under each strand end, then used the Exacto blade tip to scrape away the enamel coating on each copper strand. Then I tinned each end and attached a short section of insulated wire to each. I did the same to the strands on the other side of the burn mark. In total, I had 5 strands that were broken (that I could see). I then numbered each strand with my labelmaker, counting 1-5 on one side of the break, and 6-10 on the other side.

Now to find the continuity between each strand tip and the lugs on the yoke. These were my results:

Strand 3 <--> Left Lug
Strand 1 <--> Strand 9
Strand 2 <--> Strand 6
Strand 4 <--> Strand 7
Strand 5 <--> Strand 10
Right Lug <--> Strand 8

So, I wanted continuity from each lug, going thru all strands. I made up an arbitrary order based on my numbering order and came up with this:

Left Lug -> 3 -> 6 -> 2 -> 7 -> 4 -> 9 -> 1 -> 10 -> 5 -> 8 -> Right Lug

So, I would be connecting 3 & 6, 2 & 7, 4 & 9, 1 & 10, and 5 & 8 - which I did. I then used some of my wife's Red Wine enamel nail polish to coat the solder connection all around, making it look like I bled all over the yoke.

Okay, now I needed to see whether or not this repair was better than the first. Before, I was reading 40.3 ohms across the vertical yoke, rather than the 44.1 ohms I had been told was correct. Well, I now had an original undamaged yoke handy, so I hooked up my meter to the vertical yoke to see what it's supposed to be:

So, lets see what my "repaired" vertical yoke is now reading:

HEY! Look at that! I'm feeling pretty good now. I had to take a few minutes to go strut in front of the wife and announce, "CONFIDENCE IS HIGH! I repeat, CONFIDENCE IS HIGH!" Of course, I then had to explain what I was doing, and how difficult it was. She patted me on the head, gave me a cookie, and sent me back to test my "fixed" yoke.

(Stay tuned for a thrilling conclusion....)

 

[jehuie]

I had to take a few minutes to go strut in front of the wife and announce, "CONFIDENCE IS HIGH! I repeat, CONFIDENCE IS HIGH!" Of course, I then had to explain what I was doing, and how difficult it was. She patted me on the head, gave me a cookie, and sent me back to test my "fixed" yoke.

Ah hahaha. I can relate to that pat. This is great stuff here man.

 

[modessitt]

Okay, now to test my repair. I was a little worried that I'd have problems with either:

1) The insulated wire wouldn't let it work properly because it wasn't tightly wound like the original, or was too long, or the wrong gauge or whatever.

2) The voltage thru the yoke would burn off the insulation

3) The enamel wasn't on properly (or was the wrong type) and sparks would fly.

Well, before we test, we've got to have a control. So, I put the undamaged yoke on the tube and got this slightly blurry pic (damn camera):

Looking good. A little convergence issues on the corners and a little warping, but probably due to the yoke or rings not being on perfectly. Not worried about that at the moment. I'm just hoping that my repaired yoke gives a similar result.

So, I put the repaired yoke on and get this:

WOOHOO!!!!

It's been running for 30 minutes now and still looks just as good! Looks like I have successfully repaired a blown yoke. I'm sure it's owner is going to be VERY happy.

Hopefully this will inspire someone in the future. As for me, no more med-res monitor repairs unless I have a good yoke handy.

Peace...

 

[jehuie]

Impressive. Congrats. How difficult was it to solder to those small wires after you scraped off the insulation?

 

[modessitt]

Impressive. Congrats. How difficult was it to solder to those small wires after you scraped off the insulation?

Eh, not bad. I tinned them, then tinned my insulated wire, stuck the iron tip in there with a small blob of solder on the tip and quickly merged them. Had a fan blowing to help cool them down fast so they wouldn't separate while they cooled...

 

[Magog]

I mainly looked at the pics, here is what I gathered.

Sour Cream magically repairs monitors!

Just kidding very interesting, and way to stick to it. It is nice when something becomes a "mission" and it goes well.

Did your wife get the "confidence is high" reference?

 

[demogo]

Very cool, Mod!

Congrats!

 

[andykmv]

you are the man!

 

[dezbaz]

Well done, fantastic outcome

 

[modessitt]

Did your wife get the "confidence is high" reference?

Nope...