Can anyone offer insight on these transformers?

[RayRay]

Hey Guys.
Upon trying to repair a power supply, I've established that it has multiple fried transformers.
Now, these are not your average, properly labelled transformers, but are PCB soldered transformers in small form factor (from the black/yellow kind) and they're labelled as follows:

nt1759nl
nt1670nl
f02801590 jy 1041
nt1669nl

on some of em, "eh limited" also appears, of which I was unable to find anything (nothing on the specific models either)
Can anyone offer any assitance?

[Andy Watson]

"Black and Yellow" !  ? 

Dig around on this site. There's some, very limited, info:

https://audiocare.nl/categorieen-/246-nt1759nl-transformer.html
https://audiocare.nl/categorieen-/296-nt1670nl-transformer.html

[RayRay]

Yeah, black and yelow, like the ones on this pic:

https://www.avforums.com/attachments/1656062660826-png.1714632/

There's the traditional transformers & the pcb mount ones.
Problem is that the second kind is near impossible to replace if it goes bad, and manufactures dig em it seems.
That audiocare site isn't very useful unfortunately, but thanks for your help!

[eurgenca]

AHHH that one. Are you sure that all black/yellow box's are transformer?

[Ian.M]

It is *RARE* for switching transformers in a SMPSU to fail, as if a fault occurs elsewhere in the circuit either the line fuse blows or the protection circuits in the controller usually shut it down before transformer damage occurs.  When they do fail, there is usually extensive catastrophic damage to other parts, and even traces blown off the board, and the PSU is usually beyond economic repair.  They are almost invariably custom wound for the application and any markings are 'house' and batch codes, rather than something searchable.  Spares, if available at all, will only be from the equipment manufacturer.

[Jason Henry]

It seems you're dealing with damaged transformers labeled as nt1759nl, nt1670nl, f02801590 jy 1041, and nt1669nl, with some mentioning eh limited. Unfortunately, specific information on these models is scarce. Consider consulting the manufacturer or exploring similar replacements for the repair.

[tunk]

A few photos of the board and transformers may help.

[Haenk]

These are all custom transformers, and likely the manufacturer will not tell you the specs.
If you are really sure, these are all dead (which would be a one-in-billion case) and it is some absolutely one-of-a-kind-impossible-to-replace PSU, find someone to unwind, count, rewind. That would be expensive, of course. Make sure, you check every single component, the transformers don't fail for no reason.
Otherwise, buy a new PSU.

[coromonadalix]

same tought 

multiple fried ??  never saw that in my life,  maybe  the main one once or twice, but never all of them,   normally you have mosfets and or the driver ic  who dies, 

the fuse is the last to blow   loll

[fmashockie]

I agree with a lot of the other commenters here.  Failures of SMPS transformers are rare.  I've never seen one.

How have you determined they failed?  Easiet thing to do would be to test them for continuity.  But you need to make sure you understand the pinout of the transformer.  Sometimes pins are just there to hold the transformer to board (there's no winding attached).  Also you might be measuring across two different windings - they are not always laid out intuitively.

As others have said, most transformers are custom-made.  And the numbers on them are custom batch numbers.  The manufacturer of these transformers is unlikely to sell them to you because they have an agreement with the manufacturer of the pcb.  So they are propriety in most cases.  Also, they tend to only manufacture these transformers in large quantities so even if they would sell them, you'd have to buy hundreds of them.

Make sure you are 100% sure the transformers are bad before proceeding down this potential rabbit hole.

-Frank

[CaptDon]

By what possible means have you come to the conclusion they are all bad, local nuclear blast, house fire? Doubt any are bad. If they are all fried as you assume why waste the time and expense to service the power supply. Chances are you'll never get it to run again without blowing up more stuff.

[RayRay]

When you see large, amber-orange stains/blotches on the yellow tape of such transformers, that's a clear indication they're fried.
I've also tested em via the method explained on this video:



Just because you've never personally encountered fried PCB transformers, it doesn't mean it can't happen.
Anyhow, I guess this board's a goner.
Thanks for all of your responses.

[Ian.M]

That video is nearly totally worthless.  You cannot test a winding for the presence of a shorted turn fault using only a multimeter.  Continuity tests can only detect open-circuit windings and winding to winding shorts.

Even with a LCR meter so you can measure each winding inductance + an identical known good transformer to compare with, its difficult to detect some shorted turn faults.   

To have reasonable confidence that a switched mode transformer is actually good you need to do a ring test.  See https://www.testandmeasurementtips.com/whats-a-ring-tester-and-why-do-you-need-one-faq/
This was common practice for testing the line output transformer back in the days of CRT TVs and monitors, as their windings were potted into a housing for high voltage insulation, and there were plenty of other components in the line output stage that could cause similar fault symptoms, so burnt windings could be very hard to detect.  Even so, if an exact replacement for comparison wasn't available, it was frequently necessary to sneak a length of thin magnet or wirewrap wire through the core window to apply a shorted turn to confirm the ring tester was effective for that transformer.  If the ring test result was ambiguous but didn't change much with the external shorted turn, it most likely had one internally.

[RayRay]

That video is nearly totally worthless.  You cannot test a winding for the presence of a shorted turn fault using only a multimeter.  Continuity tests can only detect open-circuit windings and winding to winding shorts.

Even with a LCR meter so you can measure each winding inductance + an identical known good transformer to compare with, its difficult to detect some shorted turn faults.   

To have reasonable confidence that a switched mode transformer is actually good you need to do a ring test.  See https://www.testandmeasurementtips.com/whats-a-ring-tester-and-why-do-you-need-one-faq/
This was common practice for testing the line output transformer back in the days of CRT TVs and monitors, as their windings were potted into a housing for high voltage insulation, and there were plenty of other components in the line output stage that could cause similar fault symptoms, so burnt windings could be very hard to detect.  Even so, if an exact replacement for comparison wasn't available, it was frequently necessary to sneak a length of thin magnet or wirewrap wire through the core window to apply a shorted turn to confirm the ring tester was effective for that transformer.  If the ring test result was ambiguous but didn't change much with the external shorted turn, it most likely had one internally.

But if you don't get any resistance/continuity, isn't it conclusive enough? And again, they have burn marks on em, not exactly like this:
https://jestineyong.com/wp-content/uploads/2019/05/5-8.jpg
But similar (amber orange and black stains) indicating they overheated, so regardless of testing methodology, you can't possibly claim this is normal

[Ian.M]

You have to know *which* *pins* are supposed to have continuity to test them that way.  If you closely examine the transformer from underneath you may be able to determine which pins have windings connected to them, and you can then try to find the other end of each winding with a continuity tester, but that will only detect broken wires and if you have an idea of which are primary side vs secondary side, or there is a clear difference in wire size, you may be able to detect winding to winding shorts.  Shorted turns are far far more common as the insulation breakdown to cause one is much more localised.

As for brown marks, it can be hard to distinguish between those due to internal overheating and ones from adjacent parts burning out or overheating, or residue from varnish impregnation or flux residue.  If there are clear signs of distortion of the insulation tape wrap with the winding 'printing' through as a surface texture, or black char that doesn't wipe off with a drop of solvent on a rag, its probably actually overheated, but that's pretty rare.

[CaptDon]

100% chance those transformers were built to O.E.M. specs and absolutely not ordered off the shelf!! If you want to spend insane amounts of money getting replacements then talk to Pete at EPD Magnetics in Wendall North Carolina. He can unwind and rewind to exact original specs. He designs and builds to O.E.M. specs for major manufacturers and is excellent for one-off stuff. He used to be in attendance with a booth at the Dayton Ohio Hamfest every year. I think he also took over for Peter Dahl enterprises.