Author Topic: Replacing Transformer  (Read 557 times)

0 Members and 1 Guest are viewing this topic.

Offline cplusplus

  • Contributor
  • Posts: 7
  • Country: us
Replacing Transformer
« on: February 15, 2020, 02:54:00 am »
I have a transformer that has a blown fuse inside that I can't get to because the laminated core is welded shut. I've attached it's schematic.

Is it correct to say that there is a single primary winding and three secondary taps that are center-tapped? I'm unsure of what is going on for the fourth tap on the top of the primary side. The voltage leaving there is around 15v and they come straight out of the top of the transformer while everything else is through-hole.

Thank you for your time.
 

Online bob91343

  • Frequent Contributor
  • **
  • Posts: 646
  • Country: us
Re: Replacing Transformer
« Reply #1 on: February 15, 2020, 05:23:17 am »
It's just drawn that way for convenience.  Yes there are four secondary windings, each center tapped, and one primary.  If you can't get to the fuse, you are out of luck.

Having said that, you have nothing to lose by getting aggressive with the case and cutting it open somehow in hopes of getting to the fuse.  Be advised, however, that you are mucking with stuff that has safety considerations involved and you could be asking for trouble.
 
The following users thanked this post: cplusplus

Offline cplusplus

  • Contributor
  • Posts: 7
  • Country: us
Re: Replacing Transformer
« Reply #2 on: February 15, 2020, 07:45:35 am »
I meant to include that looking for the fuse was the first thing I tried. It must be pretty deep in there unfortunately.

I don't think I can find an equivalent replacement for this. It looks like my options are:
  • Use two transformers with two secondary windings external to the unit
  • Find someone to rebuild this transformer

I'm open to any suggestions or ideas I'm not aware of.
 

Offline Chris56000

  • Frequent Contributor
  • **
  • Posts: 529
  • Country: gb
Re: Replacing Transformer
« Reply #3 on: February 15, 2020, 01:17:00 pm »
Hi!

Could you give us a model no and / or a link to the Service Manual please?

The Chinese now offer a good range of "R Core" mains transformers suitable for 115/230V supplies in a very wide variety of power rantings and voltages, with two or more secondaries, and I'm sure I can draw up a repair suggestion from the Service Manual for you!

Chris Williams
It's an enigma that's what it is!! This thing's not fixed because it doesn't want to be fixed!!
 
The following users thanked this post: cplusplus

Offline cplusplus

  • Contributor
  • Posts: 7
  • Country: us
Re: Replacing Transformer
« Reply #4 on: February 15, 2020, 08:40:31 pm »
The SM is not uploaded on the internet unfortunately, but I have uploaded a more complete image I chopped together.
 

Offline james_s

  • Super Contributor
  • ***
  • Posts: 11064
  • Country: us
Re: Replacing Transformer
« Reply #5 on: February 15, 2020, 08:50:14 pm »
I repaired a transformer once that had the fuse blown by a lightning strike. It was on the top surface of the windings under just a few layers of tape, I did not have to do any major disassembly to get to it so you might try that first. My grandmother used the dishwasher for another decade after that and it was still in service when the house was sold after she passed away.
 
The following users thanked this post: cplusplus

Online bob91343

  • Frequent Contributor
  • **
  • Posts: 646
  • Country: us
Re: Replacing Transformer
« Reply #6 on: February 16, 2020, 11:03:40 pm »
There is no magic.  Just keep digging until you find it.

Another approach is to find the winding end that goes to the fuse and bring it out separately.  If there are many primary turns you can afford to go to a place on the winding instead of trying to find the end.

Of course the whole unit may not be worth all the effort.
 
The following users thanked this post: cplusplus

Offline andy3055

  • Frequent Contributor
  • **
  • Posts: 448
  • Country: us
Re: Replacing Transformer
« Reply #7 on: February 17, 2020, 01:51:18 am »
Can you post a picture?

Also, most often, the primary winding is the inner and the secondary is on the outside. According to the schematic, the fuse is on the primary and this means you may have to undo the secondaries before you get to it. That is if you can get the covers out!

But sometimes, the fuse is inserted close to the core but can be accessed from out side top or bottom.
 
The following users thanked this post: cplusplus

Offline cplusplus

  • Contributor
  • Posts: 7
  • Country: us
Re: Replacing Transformer
« Reply #8 on: February 17, 2020, 02:57:39 am »
Another approach is to find the winding end that goes to the fuse and bring it out separately.

Exciting news. There are several through-hole posts on the primary side of the transformer. While examining it, I noticed that there was an additional wire around two posts next to each other. I ran a jumper between them on the bottom of the PCB and got power again on the secondary side! I ran it for nearly an hour with no issues other than the transformer itself becoming a little warm. How can I make this safer since I can't get to the fuse inside?
 

Offline coromonadalix

  • Super Contributor
  • ***
  • Posts: 2211
  • Country: ca
Re: Replacing Transformer
« Reply #9 on: February 17, 2020, 03:27:28 am »
Normally if you bypass the thermal fuse  .. the simplest thing is : to have an primary fuse in case of ........  i would add one in the primary circuit if the schematic is the right one.


Done that in the past, never had any problems.
 

Offline Electro Detective

  • Super Contributor
  • ***
  • Posts: 2442
  • Country: au
Re: Replacing Transformer
« Reply #10 on: February 17, 2020, 09:38:20 am »

I'd be very curious/wary if jumping it bypassed a fuse, or tapped the transformer differently  ???

i.e. running warm may result in running cold eventually  :(

 

Offline TERRA Operative

  • Frequent Contributor
  • **
  • Posts: 776
  • Country: jp
  • Voider of warranties
    • Near Far Media Youtube
Re: Replacing Transformer
« Reply #11 on: February 17, 2020, 09:40:23 am »
How about sticking in one of those thermal fuses like is used in fan heaters and toasters etc in place of the busted one?
Just stick it in place with some silastic in the corner between the inner windings and the core.
Any circuit design must contain at least one part which is obsolete, two parts which are unobtainable, and three parts which are still under development.

https://www.youtube.com/user/NearFarMedia/
 


Share me

Digg  Facebook  SlashDot  Delicious  Technorati  Twitter  Google  Yahoo
Smf