LL1538 broken?

[living sounds]

I've got two LL1538, both from different members of this forum. I'm trying to get a JLM Baby Animal running with one of them but couldn't find the problem. Now it seems that both these transformers could be broken. When measuring the resistance between the secondaries (pin 5 + 6) I get nothing, open circuit. Should be 880 ohm. I already destroyed a nice 990 during fault finding and payed good money for these transformers...

What to do? Open them?

 

[living sounds]

Connecting the transformer to my converters it passes a signal, but what gets through is severely high pass filtered. Only one of the secondaries seems to carry a signal. Broken, right?

 

[Kingston]

Yes, broken unfortunately. I had a very similar issue with two LL1540 transformers. Signal would switch into this "high pass mode" you describe if input level was low enough.

I didn't have the skills to fix them and opening a Lundahl transformer is not exactly trivial. Strangely enough both of my transformers still had perfect specs...

 

[zebra50]

It's weird but I think it has to be breakdown of the very thin coating of insulation that covers the wire.

 

[Kingston]

Oh yeah should have mentioned, both of my transformers (now zebra50's actually) were very old and worn even on the outside. I seem to recall they had been extracted from some eighties broadcast desk line input modules.

 

[sahib]

Sometimes  the wire is soldered to the pins very critically and if you overheat the pins during removal they can fail. I have recently wrecked a Lundahl and a Neutrik. Normally I had no problem of removing them but this time they were pretty tightly soldered and when I measured both after removal one side showed open. I took both apart to repair and all I can say is don't bother.

So, my macho days with ordinary solder pump are now over and I am about to invest into a good desolder station.

 

[MatthisD]

Strange that they both have this problem. Are you getting 44ohms for each primary, there is only one secondary start and one secondary end pin on this transformer so did you mean only one primary carries a signal?

If the wire snapped at the pin then I wouldn't think it impossible to extend the wire and re-solder it to the pin as long as you can get the case off. Sahib might be right though the secondary wire would be very thin.

You can get an idea from the photo with the tweezers;
http://www.lundahl.se/sidor/photo_gallery.html

 

[SkunkFunk]

I've managed to damage carnhill and lundahls this way. Never tried to fix the lundahl, but the carnhill was a piece of cake. As there was no mu-metal can on it, i could see the wire that was loose. Soldered on a short extension wire, checked that it worked and covered it in hot glue. Maybe you can try to remove the can and see if the broken wire is visible.

 

[sahib]

Here is what you'll find.

Wire is indeed very thin and soldered directly onto the pin. I can't even see it. The potting agent being hard makes it very difficult to dig it out too as you'll probably break the wire further.

Now I have a Lundahl inductor.  ;D

 

[MatthisD]

Which model is that? if you don't plan to do anything with it can you PM me a price you'd take for it, I would use the lams and bobbin for diy'ing.

 

[sahib]

It is LL1540. I also have a Neutrik NT4 too.

You can have them free. Just pay the shipping.

I'll pm my paypal e-mail.

 

[living sounds]

Thanks everyone!

I peeled one of them apart, couldn't find the wire in all that gummy stuff. Defintely no connection. Couple of pictures for you:

 

[living sounds]

Nr. 2

 

[MatthisD]

You could break the wire by digging around and not realise with wire that thin. Try to melt the goo, let it drip off rather than scraping it and hopefully you can see the wire. CJ might have done one of these lundahls but I haven't seen a thread about one.

 

[living sounds]

You could break the wire by digging around and not realise with wire that thin. Try to melt the goo, let it drip off rather than scraping it and hopefully you can see the wire. CJ might have done one of these lundahls but I haven't seen a thread about one.

Thanks, I'll try heating it with the soldering station (no heat gun).

 

[living sounds]

So I tried it with heat, no chance. Couldn't even locate the wire.

 

[bruno2000]

I had some Lundhal transformers several years ago that were damaged when I pulled them from another board, but was able to repair them by re-heating the pin very hot, and pushing it back into its hole.  Then checking for connection, and securing it with a little dab of hi-temp epoxy.  They are still working today.
Best,
Bruno2000

 

[zebra50]

I would use the lams and bobbin for diy'ing.

I don't think Lundahl use bobbins. The ones I have seen are wound over very thin tape, in layers. Old-skool style, but with very thin tape. You can still use the lams of course.

Cheers

Stewart

 

[MatthisD]

Thanks, I'll try heating it with the soldering station (no heat gun).

Heat gun would be the way to melt the compound and get it to drip off rather than burning it with an iron. Not sure how the outer insulation will cope with the heat.

 

[MatthisD]

I don't think Lundahl use bobbins. The ones I have seen are wound over very thin tape, in layers. Old-skool style, but with very thin tape. You can still use the lams of course.

Cheers

Stewart

It looks like that in the photos, that must keep the production cost up.