plasma tv power board fuse keeps popping

[daryck88]

hi i have a power board model number lpx55 and the fuse keeps popping when i plug it in. any help would be great thanks...

[cashkennedy]

Re: plasma tv power board fuse keeps popping

If its the main fuse on the primary side of the power supply you might want to use a multimeter to see if the + and - of the bridge rectifier is not shorted. With the power disconected, see if the resistance is really low between the + and - pins.

Bellow is a picture of a bridge rectifier, they almost all have markings showing what each pin does.

[daryck88]

Re: plasma tv power board fuse keeps popping

If its the main fuse on the primary side of the power supply you might want to use a multimeter to see if the + and - of the bridge rectifier is not shorted. With the power disconected, see if the resistance is really low between the + and - pins.

Bellow is a picture of a bridge rectifier, they almost all have markings showing what each pin does.

how do i test them on what marking do i put the leads on and what reading do i look for on the tester and does there have to be power to the unit

[selldoor]

Re: plasma tv power board fuse keeps popping

Are you having a laugh or what? you now have 3 threads for the same set.
You have been told already how to test a Bridge rectifier - the answer will not change.

AND Cashkennedy answered your last 2 questions in the post above.

With the power disconected, see if the resistance is really low between the + and - pins.


You need to read the answers?

[daryck88]

Re: plasma tv power board fuse keeps popping

If its the main fuse on the primary side of the power supply you might want to use a multimeter to see if the + and - of the bridge rectifier is not shorted. With the power disconected, see if the resistance is really low between the + and - pins.

Bellow is a picture of a bridge rectifier, they almost all have markings showing what each pin does.

i get in between 1080 and 1090 on both of them.

[cashkennedy]

Re: plasma tv power board fuse keeps popping

Thats too borderline for me to acurately say, but other people here know more then me. If you had gotten under 200 ohms i would say the primary side of the power supply had a short somewhere in it.

You can also further test the bridge rectifier by taking diode readings and resistance between each pin.

such as - to ~ , + to ~, ~ to ~ for resitance

diode readings are more complicated and might need to be taken with the bridge rectifier removed from the board? Im not 100% sure on that. either way you have to take diode readings in every possible order, as in red on - and black on ~, then reverse them and test black on - and red on ~.

[daryck88]

Re: plasma tv power board fuse keeps popping

Thats too borderline for me to acurately say, but other people here know more then me. If you had gotten under 200 ohms i would say the primary side of the power supply had a short somewhere in it.

You can also further test the bridge rectifier by taking diode readings and resistance between each pin.

such as - to ~ , + to ~, ~ to ~ for resitance

diode readings are more complicated and might need to be taken with the bridge rectifier removed from the board? Im not 100% sure on that. either way you have to take diode readings in every possible order, as in red on - and black on ~, then reverse them and test black on - and red on ~.

now it just read 1035 for both could fluxuation mean there no good

[cashkennedy]

Re: plasma tv power board fuse keeps popping

With cheap multimeters it can be hard to make a reliable conection, as well as get a consistent reading. Thats not so alarming that i would assume its your problem.

Testing the bridge diode for a short doesnt tell you that the bridge diode is bad, it tells you that the primary side of the power supply has a short.

The way a power supply works is the AC is converted to DC and then the high voltage DC is ran through a 1 side of a tranformer, all this occurs on the primary side. On the secondary side the power appears in the transformer and then is filtered. Most power supplies have a thick white line on the board deviding the primary from the secondary, and the line will run through the middle of the transformers. the transformers have no way to cary shorts from the primary to the secondary. So if you have a short in the primary you know a part on the primary side is bad. And a short obviously from anywhere in the primary is going to instantly blow your fuse.

Typical parts to fail in the primary are the mosfets, bridge diode, or the ic's. But other things can fail.

[daryck88]

Re: plasma tv power board fuse keeps popping

With cheap multimeters it can be hard to make a reliable conection, as well as get a consistent reading. Thats not so alarming that i would assume its your problem.

Testing the bridge diode for a short doesnt tell you that the bridge diode is bad, it tells you that the primary side of the power supply has a short.

The way a power supply works is the AC is converted to DC and then the high voltage DC is ran through a 1 side of a tranformer, all this occurs on the primary side. On the secondary side the power appears in the transformer and then is filtered. Most power supplies have a thick white line on the board deviding the primary from the secondary, and the line will run through the middle of the transformers. the transformers have no way to cary shorts from the primary to the secondary. So if you have a short in the primary you know a part on the primary side is bad. And a short obviously from anywhere in the primary is going to instantly blow your fuse.






Typical parts to fail in the primary are the mosfets, bridge diode, or the ic's. But other things can fail.

do those pieces you mentioned burn out by themseleves or can an other part from the tv burn them out?

[cashkennedy]

Re: plasma tv power board fuse keeps popping

Parts in the primary side of the power supply burn out usually from bad part design / quality (as with almost all the problems with modern electronics ), or from power surges / dirty power, or from being too hot.

Ive never personally seen it occur, but perhaps if a tv is consistently using too much power it would be able to wear out the parts on the primary. But almost all the boards have fuses themself, which should prevent the other individual boards from drawing too much power.

[daryck88]

Re: plasma tv power board fuse keeps popping

Parts in the primary side of the power supply burn out usually from bad part design / quality (as with almost all the problems with modern electronics ), or from power surges / dirty power, or from being too hot.

Ive never personally seen it occur, but perhaps if a tv is consistently using too much power it would be able to wear out the parts on the primary. But almost all the boards have fuses themself, which should prevent the other individual boards from drawing too much power.

all the other fuses on the other boards are fine im kindda confussed with all this stuff and just want to buy a new board but dont want to burn it out.not sure wat to do.

[selldoor]

Re: plasma tv power board fuse keeps popping

Testing a Bridge rectifier.

I really thought you had sorted this having seen the video and been told but I will go through it again step by step.

If the Bridge rectifier is still on the board find the pin designations (probably as in the picture in post 2)

Get a felt tip pin and follow the pins through the board and mark the board
+ a c -
0 0 0 0 (This line is just to represent pins)
1 2 3 4
Mains power OFF
Set your meter to measure 2000 ohms.

Place positive (red) probe on the + pin. 1 above
Place negative (black) probe on the ac pin 2 above.
Write down the result. ohms

Place positive (red) probe on the ac pin. 2 above
Place negative (black) probe on the + pin 1 above.
Write down the result ohms

Place positive (red) probe on the ac pin. 2 above
Place negative (black) probe on the ac pin 3 above.
Write down the result ohms

Place positive (red) probe on the ac pin. 3 above
Place negative (black) probe on the ac pin 2 above.
Write down the result ohms

Place positive (red) probe on the ac pin. 3 above
Place negative (black) probe on the - pin 4 above.
Write down the result ohms

Place positive (red) probe on the - pin. 4 above
Place negative (black) probe on the ac pin 3 above.
Write down the result. ohms

You can cut and past the above and write in your results.

I have not re read your other posts but here you say you have tested all
the fuses on the other boards - were these glass tube fuses or have you checked the smd fuses,if there are any, some of which may be on the back of the boards. However none of the other boards would make your PS board
blow a fuse as soon as it is plugged in.

[cashkennedy]

Re: plasma tv power board fuse keeps popping

I was never actually formally told how to test a bridge rectifier. Plain bill just posted a picture of 4 diodes in a circle (what a bridge rec actually is), and was like figure it out!

In response to your question on whether replacing the power board is likely to help: yes, theres at least a 90% chance that your problem is in the primary of the power supply, but you might have other problems in the set, and the price to fix parts on the primary (if you can solder), is usually really cheap and easy vs buying a new power board. So if you dont have a soldering iron, or know someone with one, then your best bet is probably to just buy a power board.

[selldoor]

Re: plasma tv power board fuse keeps popping

@CK
Hi - for info, the film I mentioned is here http://www.youtube.com/watch?v=dqkT6hF0O3E.

The results you should get are + to ac high ohms one way nil opposite (as with a diode) - to ac the same. Ac to Ac is just checking for a short.
You can see the results on the meter right at the top.

In circuit, the results are not as clear cut due to other components but usually it is high ohms one way and low ohms with the leads reversed.
If results show up a short or results are close together it would need to be
removed for out of circuit test.

[daryck88]

Re: plasma tv power board fuse keeps popping

Testing a Bridge rectifier.

I really thought you had sorted this having seen the video and been told but I will go through it again step by step.

If the Bridge rectifier is still on the board find the pin designations (probably as in the picture in post 2)

Get a felt tip pin and follow the pins through the board and mark the board
+ a c -
0 0 0 0 (This line is just to represent pins)
1 2 3 4
Mains power OFF
Set your meter to measure 2000 ohms.

Place positive (red) probe on the + pin. 1 above
Place negative (black) probe on the ac pin 2 above.
Write down the result. ohms

Place positive (red) probe on the ac pin. 2 above
Place negative (black) probe on the + pin 1 above.
Write down the result ohms

Place positive (red) probe on the ac pin. 2 above
Place negative (black) probe on the ac pin 3 above.
Write down the result ohms

Place positive (red) probe on the ac pin. 3 above
Place negative (black) probe on the ac pin 2 above.
Write down the result ohms

Place positive (red) probe on the ac pin. 3 above
Place negative (black) probe on the - pin 4 above.
Write down the result ohms

Place positive (red) probe on the - pin. 4 above
Place negative (black) probe on the ac pin 3 above.
Write down the result. ohms

You can cut and past the above and write in your results.

I have not re read your other posts but here you say you have tested all
the fuses on the other boards - were these glass tube fuses or have you checked the smd fuses,if there are any, some of which may be on the back of the boards. However none of the other boards would make your PS board
blow a fuse as soon as it is plugged in.

i only get a reading when i put the red lead on the positive leg and the black lead on the negitive every other configuration gives me nothing.

[cashkennedy]

Re: plasma tv power board fuse keeps popping

Nothing as in, more then 2000 ohms so your multimeter displays a 1 ___ , or nothing as in 0 ohms?

[daryck88]

Re: plasma tv power board fuse keeps popping

Nothing as in, more then 2000 ohms so your multimeter displays a 1 ___ , or nothing as in 0 ohms?

0 ohms

[cashkennedy]

Re: plasma tv power board fuse keeps popping

Thats not the failure state i would expect, but if your really getting 0 resistance between both AC leads, then you either have a bad bridge rectifier, or a short in the very few parts that are before the bridge rectifier (usually theres the power cord > fuse > a few inductors > then the bridge rectifier. )

You could unsolder the bridge rectifier and do some proper testing on it out of circuit. http://www.ehow.com/how_7918714_test...rectifier.html