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Hi everyone, I harvested this transformer from a Mitsubishi TV, it has two red wires on one side and two white wires on the other side, there is a tag that says 350P43902 witch I believe is the part number and 24F049HD witch I believe is the part name also it says TAM and M 9408. I want to know what this transformer does?  I tried to find the datasheet for it but had no luck looking online, so if anyone can help if they know what it is or where to find its datasheet online I appreciate it as I like to see what I can use it for, maybe somewhere in my flyback transformer project. Thank you.


It looks like the main power transformer, the output will be 12V or something like.


So if the red wires are thin and hook to thin multiple windings, and the white wires are thick and hook to a few windings of thick wire then witch one is the prim and sec? assuming its a step down.

You ought to know which wires are which because you said that you took it out of a TV yourself; what were they connected to originally?


Well the wires were going to the circuit it was hard to tell what was what but perhaps I didint pay too much attention at the time, im sure had i looked i would have seen sum pair going to a part of the circuit that has nothing to do with the mains.

Yeah, trace it back like that.
Next time remember to label the wires before you take them off. Or just cut them so you've got a stump left and then you know where they were connected.


Actually the end of each pair of wires has flares witch go into these plastic connectors where the wires were pushed in , one connector was labeled JA and the other JB , when i took the wires out i did mark them but the markings have rubbed out , I can almost make one out to be JA on the red wire I traced it back and JA goes on the main chasis board next to sum inductor looking device it has exposed copper coils that are wrapped around this white plastic looks like two barrel of copper coils next to each other in some housing, so i think maybe the red wires are suppose to be the mains primary but maybe not directly, also if I recall the white wires went to a small circuit that is at the but of the CRT or electron tube. I did keep all circuits but I cannot trace the white ones on the small circuit yet, maybe I was wrong about the white wires i just dont recall.

Yes I reckon the red ones should be connected to AC mains (carefully).


yep i found the white wires go to the same board but they seem to be further then where the power cable comes in so I do think it was red ones that go to main.

But I think it might be damaged or compromised,,,oh well too bad.

Yea, I did this to a transformer once, think I was 14.
I didn't do it again.


What you did: sum poping noises as the trans was cooking there was this sweet burning smell.


yep it cooked a bit and i think it must of damaged the primary internally cause I tried again doing the test on both sides and I get low readings so it possibly compromised the ratio.

You've melted a wire; the winding is broken like the transformer.


what do you mean like the transformer? we are only talking about the trans in the pic and yes it musta melted a wire somewhere in the primary and compromised the ratio from 120 to 12 to 120 and something else like 4 volts.

Ok I wish you answered me faster about why the light bulb was needed , now I think I know why,,,, I screwed up, I took the bulb off and closed the circuit,, ooops there was sum buzing noises, the needle went across and then sum poping noises as the trans was cooking there was this sweet burning smell so I quickly disconnected the power,, I tried it again with the bulb on the circuit but it was not lighting I think the trans is fried now my god these things burn so easly??.

So the bulb was acting like a current limiter or something, ok so I also think the trans was working before and the reason why the needle did not move was probably cause it was set for 150 Vac when it should have been set to 15 since most likely the trans was outputting 12 volts or something in that low range correct?

Basic rules of electricity always start with high scale on any meter.

Any XFMR can be a step up or step down if reversed .

It could have been that it was the low voltage secondary you put
directly across the line.

Yes the light bulb was limiting the current if you wired it wrong.

Experience is a strict teacher :-)

1)what is an XFMR? is it a trans? and wont it damage it if you reverse it and put high current on say the low voltage secondary? in theory it should step up but only if the low voltage side can accomodate the high current right?

2)I put the thinnest wires to the mains like you said, so you could have been wrong then?

3) I can understand how the light bulb would limit the AC when the current is going thru the bulb first then to the trans but what happens when the current is reversed and it is going thru the trans first then the bulb during the cycling? isint the trans geting hot about 50% of the time???? as I said I'm not to savvy about this stuff, electricity is like one of those enigmas to me and it cant be explained as flowing water not when its AC lol to complicated.

XFMR is short for transformer some guys call the MOT.

Except for a tiny amount the XFMR Power in = Power out
So a 12VAC 10A secondary will draw 1A at 120VAC on the primary
The step down xfmr reduces 120v to 12v ( 10:1 ) and at the same time
it transforms 1A to 10 Amps both ratios are 10 and 120x1 = 120 = 12x10...

2) I presume you looked at the magnet copper wires attaches to the
terminals of the xfmr.

3) AC current is identical in either direction, except when
semiconductors are used.

MOT are microwave trans,,have no idea what XFMR means?

when you told me to use the thinner wires I was looking at the leads not the coils, but yes when I look inside I see that the thinner red wires (leads) are hooked to thin magnetic or cooper wires making the coils on one side and the other side are thicker coil wires that are silver in color maybe aluminum or another type of uncoated steel wire.

your third explanation about AC still made no sense as far as what I was trying to understand,,, if current is passing thru bulb first then it makes sense since the bulb is taking most of the heat, but what happens when the current with all that heat is reversed on the cycle and passes thru the trans first ?? how can the bulb be getting all the heat when the cycle is such that the current passes thru the trans first?????

Silver is the solder.
Current does not transfer heat it only generates repetitive heat.

It the lamp impedance is small compared to the primary winding
the lamp will be dim and indicate safe to apply full line power..

On the other hand if the lamp impedance is large compared to the
secondary winding the lamp will be bright and do not attempt to
power it from the line..

heat is a product of voltage across a device and the current through it....

I can tell the difference between solder and wire, the thicker wire was not copper coated it was just bare steel looking wire like you find in 14 gauge electrical wire.

from what I understand, voltage is only the driving force and current is what I associate with amps or what creates heat , voltage will give shocks but amps will kill. I made 48Kv arcs with my FBT and they did not heat my electrodes at all, but when I had another type of arc witch had more amps it heated up one of the electrodes red hot.

the first time i hooked the lamp it was bright and it was hooked to the red wires witch were going to thin copper coated wires. According to you these were suppose to be the primaries.

when i hooked the lamp to the white wires witch were hooked to the thicker coil wires it was dim or less bright. So am i to assume that these white wires with thicker coils is the primary? than this would make it a step up trans right?
since primary has fewer turns and is hooked to 120v then sec has thiner more coils and is higher output volatge.

Consider a 12VAC transformer.

The Primary of a step down transformer
  • Wires to the mains 120 VAC supply input
  • Has the smaller gauge wire
  • Has about ten times more turns
  • Usually the inside winding
  • Has less current flow
  • Has the high voltage
  • Is the high DC resistance
  • The test lamp is dimmer on the mains

The Secondary of a step down transformer
  • Are the 12 VAC output wires
  • Has the larger gauge wire
  • Has about ten times less turns
  • Usually the outside winding
  • Delivers ten times more current
  • Delivers ten times less voltage
  • Is the low DC resistance
  • The test lamp is brighter on the mains

The magnet wires are Solid copper windings with an insulating material.
The ends are stripped down to bare wire  so it will accept solder on the
pre-solder tinned terminals.

I agree with everything you said and it makes sense.

Here are some things I want to point out on my trans:

1) both red and white wires say 22AWG , but the white wires are thicker? or is this just thicker insulation? what does this tell us?.

2) white wires seem to be attached to thicker exposed wires I could not see well inside but i do see about two exposed wires wraped around some whitish epoxy these may be just leads to the white wires or perhaps they are the coils.

3) red wires are attached to thin copper coils.

4) lightbulb is brighter on red mains wires.

5)lightbulb is dimer on white mains wires.

when i did the test i did what u said and attached the bulb and red thin wires to mains,, this gave bright bulb,,u now say not to do that? i later put bulb on white thick wires to mains and light was less bright.

so what can you conclude from this?


6 years ago

Test that transformer with a 40W lightbulb on the thinnest wires
and measure the voltage on the output
measure the input and compare the ratio.

If the bulb is not too bright try it with a 60W bulb
and if probable a 100W bulb.


1)Ok I did this test but instead of a light bulb I used one of those mains testers that have a small bulb that glows orange when the wires are live, the bulb glowed but there was no measurement on the voltmeter???? so is my transformer secondaries fried?.

2)My mains is 120V at 60HZ so put the voltmeter on 150 Vac as the only options are 15 ,150 and 1000, the display needle has up to 15 V only? so do I have to multiply this by 10 wherever the needle ends up provided I have it set at 150?.

3)I tested the mains directly with my voltmeter and the needle was close to 15 or 150 it seemed like I was getting around 130-140Vac ? shouldn't it be only 120? or is 120 more like an rms value so they give it more juice in order to accommodate a load while averaging around 120?

4)What would happen if I reversed the connections and plugged the white wires to the bulb and main?

5)Anyways I got no reading on the voltmeter what does this mean please?.

1) 4) 5) Can't help someone who deviates from Best engineering advice direction. Readings are meaningless.

2) times ten yes.

3) Measuring mains where you live at different times of day can vary all over
from 90 VAC to 140 VAC all readings are assumed RMS.

Its probably what L said.

Best eng advice lol ,,, ok ok so I used another bulb that came handy with those wires sticking out of it, so what is the diff? the bulb receives both amps and volts no?

what is L????

lol what makes you think hes a UK PHD? I assume ur joking

I have been here a few weeks, i guess im not familliar with the other thousands of users.

Now going back to my transformer, if it was working properly and was 120 to 12 v then am I correct in thinking that the mains can be directly hooked to the thin red wires and this will allow me to get a reading of 12v on my voltmeter witch is connected to the secondary thicker white wires?.

That is a small gas light bulb.
If you want answers you need to feed some current into the XFMR
and that is what the incandescent bulb does without the chance
that the XFMR wired to AC line will blow up in your face.

A neon tester shows presence of voltage only @3$% !!!!

Oh L is the other reply ok

Well I did this setup again using a 100W bulb and it worked but the needle only read about 1.5V?? I think its because the bulb was drawing to much and not allowing enough current to pass to the secondary, maybe if i tried with 40 W it will read higher but if it really is a 120 to 12V step down then why was it not working when I hooked it directly to the mains without bulb??? it was geting fried instead?

There is a distinct probability that when you smelled the sweet smell the xfmr
was damaged ( fried is the EE term ) and you now have shorted turns.

Then you mentioned the needle of your meter wanged over to the side, you now have a compromised system.

A 100W bulb is the strongest drive power.
The 40W is the lowest power first intended drive.

It was getting fried because the magnetic design of a 12VAC output cannot
support 120 VAC without saturating the iron core and driving the xfmr into a
hot toaster oven.

I think something got shorted and compromised because I tried the test in reverse using the sec wires as the primary and the bulb lit less brightly and instead of 1.5V I was getting 1 volt? I have no idea what is going on anymore, as I told you when I first had the trans I tested both sides for continuity and the Neel went all the way across on both pair of wires? is this normal?.

if 100W was strongest drive then why was I only getting 1.5v out when it should have been 12v??. Isint the strongest and most accurate test to simply hook the trans directly to the mains?.

I never said that I put 120V on the low 12 volt sec side??? I said I simply removed the bulb and hooked the primary directly in the mains that's when it fried , still don't know why this happened ? besides did int you say that trans can be reversed from step down to step up? I am the one who thought this would not work cause the low side is not made to handle it not unless I am using low voltages like say 12 to 36v like batteries ,,,However I did try this and the bulb glowed weaker and I only got 1 v instead of 1.5 .

In any case I think the whole thing is shot.

1)OK i didint know that , it looked like the little coils inside the bulb were drawing lots of amps? but the point is that it was working, power was still being routed thru the primary so there must have been volatge and sum amps going trhu so why was there nothing on sec side?

2)supposing I did the test with incandescent bulbs and still got no output on my voltmeter? but i had continuity on sec side when tested on voltmeter?

3)Also I thought trans are usually hooked directly into mains without need of some resistance is this no how they work? I guess the bulb was just there for safety, but why did it cook when i took the bulb off? I am quite sure we had the right wires going to the mains, I did like you said and used the smaller wires.

1)I am not to savvy about electrical stuff but I did a continuity test on the red and white wires of the transformer and both had good continuity the needle on my voltmeter went all the way across?

2) This made no sense to me, I thought if you apply a resistance across the wires like the coils of a transformer the needle will only go up slightly since there is resistance.

3) if both sides of trans are ok then why was there no reading on voltmeter when I was doing bulb test? does this mean that maybe the iron core is broken?

Thank you for the reply and the effort to do a nice schematic.

1) I think the slightly thinner wires are the red ones are these suppose to be the primaries? and the ones I should hook to the mains along with the bulb?.

2) So the thicker white wires are the secondaries witch I should hook to the voltmeter? I thought the thick ones were suppose to be the primary or the ones that receive the larger voltage?

3) Is the lightbulb acting like a ballast or some sort of safety resistance? because the higher the wattage the more current it will pull correct?

4) I need to be sure what I am hooking to what as I don't want to risk burning it or making a fire or does this even matter as long as I got a bulb on?

5) You think this is a step down transformer?

6) What is the point of this test? to tell me what the step down ratio of the transformer is?

7) Do I really need the bulb?

8) My voltmeter is analog and not digital will this be ok?

It seems that after my mishap I thought the trans was fried but it wasn't working because the circuit breaker on my power-bar tripped, so I retried it and the bulb worked again but unfortunately I still got no reading on my voltmeter even when set at 15Vac hmmm so I guess there is still something wrong with the trans.

iceng I would still appreciate it if you went over all my comments and answered every numbered question on them thanks again.

iceng can you please go over ALL my replies and answer every numbered questions?

thank you very much