Is this transformer bad? (Measurements inside)

[orientalsniper]

Hello all, I have never tested a transformer before, this is the reading (out of circuit) I got:

1-(2-6) = open
7-(2-6) = open
1-7 = 0 ohm

1-8 = 4 Mohms
1-9 = 7 Mohms

7-8 = 0.5 Mohms
7-9 = 3 Mohms

I attached picture of transformer with the pins sequence. It's an IT-003 inverter transformer.

If it's bad, do I have to find an exact replacement? I have lots of dead PSU's laying around, the transformers are not the same, how do I solder them to test on the inverter board?

Problem with monitor is going dark after 2 seconds (the backlight, power LED is still powered on).

[budm]

Re: Is this transformer bad? (Measurements inside)

Looking at your picture, Pin 1 & 7 are for the Primary winding, it will have very Low OHM.
Pin 8 & 9 are for the high Voltage winding, typical value can be from 500~1K Ohms range.
Compare the readings of this transformer with the other one that is the same as this one.

[orientalsniper]

Re: Is this transformer bad? (Measurements inside)

Hey, thanks for your reply, I don't have another similar inverter transformer, what I meant was that I had tons of transformer for power supplies.

Can I use those? They don't even have the same amount of pins.

[munja]

Re: Is this transformer bad? (Measurements inside)

1 & 7 are primary winding 0,2-0,5 OHMs,8 & 9 are secondary winding and value can be 500-1,5 KOHM .....your transformer is bad.....between primary and secondary is infinite resistance

[budm]

Re: Is this transformer bad? (Measurements inside)

Nope, you have to get the same one.
What kind of monitor is this that uses only one small inverter transformer?
Inverter transformer output voltage is around 1500V start and then drops down to about 800~1000V once the lamp is on.

[orientalsniper]

Re: Is this transformer bad? (Measurements inside)

It's an LG W1943. Forgive me if I'm wrong, so if 8 and 9 are secondaries, they should be shorting right?

Because, measuring pin 8 against pin 9, I'm getting 0.9 Kohms.

[budm]

Re: Is this transformer bad? (Measurements inside)

"Because, measuring pin 8 against pin 9, I'm getting 0.9 Kohms." That is about right.
It may have lamp problem, power supply problem, inverter circuit problem, etc.

[orientalsniper]

Re: Is this transformer bad? (Measurements inside)

Thank you both! I will order a new transformer.

[budm]

Re: Is this transformer bad? (Measurements inside)

Thank you both! I will order a new transformer.

I doubt that it is bad transformer. The mega ohms reading may be due to your hands are on the probes and it shows your body resistance.

[stj]

Re: Is this transformer bad? (Measurements inside)

try it wih a cfl instead of the original lamp(s)

[orientalsniper]

Re: Is this transformer bad? (Measurements inside)

I doubt that it is bad transformer. The mega ohms reading may be due to your hands are on the probes and it shows your body resistance.

My bad! I misread your reply, you were right, that was my body resistance, primary against secondary reads infinity.

I don't think it's the lamp, because I'm having same problem with my inverter tester (turns off after 2 seconds).

Here's photo of tester: http://i.imgur.com/iyWbEBR.jpg

Thank you. At least I know transformer is good, so I can keep testing the other components.

[stj]

Re: Is this transformer bad? (Measurements inside)

the 8pin chip on the right is the fet that drives the transformer,
the big cap on it's side try's to stop the circuit effecting anyting else.

how does that tester work?

[orientalsniper]

Re: Is this transformer bad? (Measurements inside)

The little lamp above the words "Inverter Tester" is a small lamp. I plug it into inverter boards and it should light up.

About the 8-pin mosfet, pin 2 has 3V for only 2 seconds. and the big capacitor has 12V always. I'm checking the schematics for more information.

[stj]

Re: Is this transformer bad? (Measurements inside)

the controller chip is shutting down drive to the fet.

[orientalsniper]

Re: Is this transformer bad? (Measurements inside)

By controller, I assume you mean the inverter driver:

Should I replace the IC or bridging 3V to pin2 of FET should be enough?

[budm]

Re: Is this transformer bad? (Measurements inside)

Check the resistance between the Source and the Drain pin of the power MOSFETs that drives the inverter transformer to see if it shows any resistance.

[orientalsniper]

Re: Is this transformer bad? (Measurements inside)

I think mosfet is fine, N channel is 10 Mohms and P channel is 3 Mohms. (Resistance between Source and Drain according to: )

[orientalsniper]

Re: Is this transformer bad? (Measurements inside)

My bad! I was testing in circuit, out of circuit, N channel has infinite resistance, so I guess the mosfet is the one with issues, can I jump any pin without replacing this mosfet?

[stj]

Re: Is this transformer bad? (Measurements inside)

no jumping of anything.