Transformer fixing problem (220v input to 12v output)

[iori3310]

Hello to all.

I am new to this forum and I am very much hoping to have some helpful suggestions here. Also, if I post in the wrong section or post anything wrong, Please let me know.

So, here's my story. I was trying to fix an audio PCB amplifier board with lots of faulty issues (I will post the entire story of this in this forum). Then suddenly while checking the power continuation on the PCB board, something triggered on the transformer side and I saw a little spark. After that I checked with the multimeter and found out that there was no voltage output on the secondary winding side (12v output side)

. I opened the transformer part by part and checked that there was a small fuse named AUPO A4F 130° 2A 250V~

, soldered with one of the wires on the primary winding side. I check the fuse and it was cut off (checked with multimeter). As, I went to the market to replace the fuse but could not found the exact one. Rather replacing the exact one, the shopkeeper offered me similar cut off fuse named N 143 958 2A 145° C

. I checked this fuse and it seemed fine with the multimeter. While attaching the fuse with the copper wire I broke the other copper wire layout attached with one of the AC input wire on the primary side (white color wire from the transformer picture). Then I had to undo the whole copper wire winding of the Primary winding side. During this process I broke the copper wire couple of times and joined them by twisting the heads of the wires together like this

. Then fixed the broken AC input wire by attaching it with the previously broken copper wire by slightly extending the on the output side side. After that I put everything part by part as it was before. Then I attached the AC input wires to the primary winding side and saw that there was no voltage output on the secondary output side (12v output).

Now I am very much confused and disappointed. I think I did something wrong but I don't know what it is.

If anyone can help me please do so. I am very much worried about this project as it is to fix my audio speakers for the PC.

Thanks in advanced
Iori

 

[MaxHeadRoom78]

Measure the continuity of each winding.
Those buried fuses are a darn nuisance, just short it out and make sure you have a separate light fuse on the input to the transformer.
IOW, forget the temperature fuses.
Max.

 

[alec_t]

joined them by twisting the heads of the wires together

Did you strip off any enamel insulation before joining the ends that way?

 

[iori3310]

To Max:

Did you suggest me to remove the fuse and use the wire directly to the Input AC? And you have to explain how to add separate light bulb fuse. I am a little confused on how you suggested me that. I checked continuity on the secondary winding and it's okay (Multimeter beeps). But when I check continuity on the primary winding, my multimeter doesn't beep. And I don't know why. I checked the fuse and it's okay.

To Alec:
No, I did not do anything else.

Waiting for some solid suggestion here.

 

[alec_t]

No, I did not do anything else.

Then if the wire is enamelled copper (typical wire used in transformers), just twisting the wires together doesn't make an electrical connection. You would need to remove the enamel from the wire ends before twisting them together and/or soldering the wire ends together.

 

[MaxHeadRoom78]

As Alec says, makes sure you remove the enamel from the wire and connect/solder the ends together and if possible put a small heat shrink or other sleeve the join.
Check with meter for primary continuity.
A separate 3AG style glass fuse can be used externally in one primary lead, 0.5a to 1a should be ample.
Max.

 

[iori3310]

Hello.

Sorry for replying late. Here are my primary and winding wire types

as Alec said, I did remove enamel from the secondary winding wire and attached it with the output wire of 12v. But I cannot remove enamel from the primary wire winding because it is too thin to be rubbed by emery paper and gets broken.

Please help I am worried about the transformer.

 

[rjenkinsgb]

Twist the ends of the primary together, then very briefly pass a gas flame under the very ends of them (eg. a cigarette lighter) so the wire passes through the blue portion of the flame.

That should burn off the enamel and leave them ready to solder.

Or:
A lot of newer transformer wire actually uses "solder through" enamel, so if you just keep the soldering iron on the twisted ends and keep adding a small amount of solder (for fresh flux) every few seconds, you should find that the enamel melts back up the wire, allowing the solder to flow.