Repairing pcb, help identifying transformer - Page 1
Forum section: electronics / repair

author: pj
author_rank: Contributor
timestamp: April 14, 2023, 11:35:35 am
content: Hi all,I'm trying to repair a pcb and would appreciate some help trying to identify a transformer part. The board drives a 24V DC fan, the fan output was obstructed and this seems to have damaged the board. I have identified that the transformer has a valid voltage at the input but nothing on the output so I'm assuming it has been damaged.From what I have discovered so far the pcb takes 240V AC, has some form of rectifier which results in 150V DC going into the transformer. The transformer has two outputs, 24V DC and possibly 5V.The only marking on the part is a label "3302-0010-01a" which doesn't seem to yield anything on google. Looking at the yellow colour I'm thinking it maybe a Wurth part as these all seem to have this yellow wrapping.Any help appreciated.

author: wraper
author_rank: Unknown
timestamp: April 14, 2023, 11:43:12 am
content: Quote from: pj on April 14, 2023, 11:35:35 amThese two things do not add up. First of all transformers do not take DC. Secondly this is a high frequency transformer which is a part of a switch mode power supply. Measure winding resistances first. What I assume, you made a garbage measurement between 2 separate windings (main and auxiliary) on the primary side. Also such transformers are custom made in 99% of the cases.

author: pj
author_rank: Contributor
timestamp: April 14, 2023, 11:54:53 am
content: Quote from: wraper on April 14, 2023, 11:43:12 amThanks I did wonder that! The windings have a low resistance on both side so maybe the transformer is ok after all.Considering I am seeing a DC input to the transformer maybe the problem is in some other component before the transformer. I will have to investigate the other parts.

author: jonpaul
author_rank: Super Contributor
timestamp: April 14, 2023, 12:00:21 pm
content: Usual cheap SMPS,Chack for blown switch transistor and driver IC. transformer is custome made and probably not the ssue.Chance to repair is nil, new one is $5..10 from Chinaj

author: pj
author_rank: Contributor
timestamp: April 14, 2023, 12:20:32 pm
content: Thanks for the tips, there is a $5 TOP256YN IC before the transformer. Looking at the datasheet it looks like my board does have a similar layout so I might replace this part see if it helps. All the other parts are diodes and capacitors that seem ok.Unfortunately this power supply is integrated into a bigger board that costs over $300 so if I can fix this part it will save some cash.

author: wraper
author_rank: Unknown
timestamp: April 14, 2023, 02:31:55 pm
content: Check if rectified mains voltage is around 340V DC. If it's not, you should look for that issue first. Just in case, do not order TOP256YN from China or ebay sellers. It's way too common they sell relabeled lower power versions.

author: pj
author_rank: Contributor
timestamp: April 14, 2023, 03:51:31 pm
content: Quote from: wraper on April 14, 2023, 02:31:55 pmThanks for the tip I have ordered some from digikey.If the mains voltage is 230V AC shouldn't the rectified voltage be more like 150V DC?

author: mariush
author_rank: Super Contributor
timestamp: April 14, 2023, 03:58:57 pm
content: 230v AC rectified to DC will produce a peak voltage of V dc peak = sqrt (2) x Vac - 2 x voltage drop on rectifier diode = ~ 325vIf the transformer is bad (maybe winding overheated and wire melted, of internal temperature fuse blew), you could determine what output voltage was supposed to be by looking at the feedback resistors and just use a third party ready made power supply and just connect the output of that board to the traces which have the output capacitor. of the original power supply.

author: pj
author_rank: Contributor
timestamp: April 14, 2023, 04:09:34 pm
content: Quote from: mariush on April 14, 2023, 03:58:57 pmOk thanks I understand now, the mains voltage is an RMS value not a peak.That's a good simple idea, I know the output should be 24V so I could pickup a cheap power supply and hook it in.

author: pj
author_rank: Contributor
timestamp: April 21, 2023, 01:05:12 pm
content: Thanks everyone, replaced the TOP256YN and board is up and running again