identifying a transformer from a power board - Page 1
Forum section: electronics / repair

author: ewcc
author_rank: Contributor
timestamp: August 22, 2020, 09:34:30 am
content: Hi,I have a transformer that I got from a tv power board.It has the following printed on the side:QQS0444-001D2 03U ST 03-AMight anyone know what this transformer is?Primary side:Pin 1 is cut.Pin 2 and pin 3 are continuous.Pin 4 is not connectedPin 5 and 6 are continuousPin 7 and 8 are continuousSecondary:Pin 9 isn't connectedPin 10 and 11 are continuousPin 12 isn't connectedPin 13 and 14 are continuousPin 15 and 16 are continuousIf they are continuous, doesn't it mean there isn't a short and thusly should be ok?The reason why I'm asking about this transformer is because when it's in circuit, when I test out the secondary side voltage, I'm getting 0 or < 1 V when I should be getting around 24 V (for pins 15 and 16).Any help appreciated. Thanks!EdAddendum: I've found the schematic of the powerboard and have attached it to this message.

author: Nusa
author_rank: Super Contributor
timestamp: August 22, 2020, 09:48:20 am
content: Quote from: ewcc on August 22, 2020, 09:34:30 amA short is the definition of continuous. It does mean there isn't an open. It doesn't say anything about ok-ness.

author: ewcc
author_rank: Contributor
timestamp: August 23, 2020, 12:41:34 am
content: Quote from: Nusa on August 22, 2020, 09:48:20 amHi Nusa,Thanks. When I place it back into the board, and powered it, the secondary side is not getting any voltage whenit should (on pin 15) have 24V. So I believe the transformer is dead; though I'm not quite sure how come.Might anyone know how I can find a replacement?ThanksEd

author: MarkF
author_rank: Super Contributor
timestamp: August 23, 2020, 03:04:32 am
content: It seems unlikely that the transformer would be dead.Especially since you have continuity between all the coils and no shorts.You have a switching power supply and more likely the problem is on the primary side.It should be pretty easy to check the passives for anything obvious.I would guess the problem is more likely the switching controller (in purple).Probing switching power supplies with a scope is very dicey.Very easy to blow up you and your scope without the proper probes!

author: ewcc
author_rank: Contributor
timestamp: August 24, 2020, 02:10:07 pm
content: Hi MarkF,Thank you for helping me with a different view of the issue. The reason why I felt the transformer was dead because I measured 200+V in the primaryside (though now, I'm not getting 1/2 that amount) so something busted again) but measured zero in the secondary for all pins. So I had thought thatthe transformer died. With your additional help, I'll check the K950x 'things' (what components are represented by K? They're continuous..so I don't get it).The switching controller could be problematic since I'm supposed to measure 300+V but I only get 100 in the drain. It's a power IC; but according to my search, the STR Y6456 is an obsolete item. If this ic is indeed dead, what would be the best replacement? I've looked at digikey but I can't make heads or tails as to which power IC is the right one. Any help definitely appreciated.Will continue to work on this project. Thanks for the immense help.

author: MarkF
author_rank: Super Contributor
timestamp: August 24, 2020, 03:21:14 pm
content: I really can't help you much more with switching power supplies.I only know enough to be dangerous and that they are dangerous to work on.So, be very careful probing it.

author: TheMG
author_rank: Frequent Contributor
timestamp: August 24, 2020, 06:51:54 pm
content: Transformers in switching power supplies have very few turns compared to a mains frequency transformer since they run at such high frequencies (tens of kHz typically). Thus, the DC resistance reading of any of the windings is going to be very low, in the sub-1ohm range. Practically a dead short at DC.The only thing you can test for with a DMM is for open windings, and shorts between windings that should be isolated from one another. Most of the time, if an SMPS transformer fails it fails open from a break where the winding connects to the pin. Shorted failures are exceedingly rare except in very poorly constructed units (the kind you are likely to find in $2 USB chargers off eBay).Most faults with SMPS are failure of capacitors either on primary or secondary side or both, or semiconductor failures particularly the primary switching transistors and control IC.

author: ewcc
author_rank: Contributor
timestamp: December 07, 2020, 07:42:05 am
content: Quote from: MarkF on August 23, 2020, 03:04:32 amYou are correct. It wasn't the transformer that was busted, which is very thankful.There were a few items on that board that were bad.