phillips lcd keeps blowing fuse

[TimT]

Re: phillips lcd keeps blowing fuse

meter set to 2 im getting 0 in standby the only reading im getting is when the backlight flashes. reading .077 the after the flash it's back to 0. tested this several times with readings ranging from .007 to .055 im thinking the flash is to quick for my meter to read. .077 was the highest reading. thinking this is closer to the true value.

[budm]

Re: phillips lcd keeps blowing fuse

OK, let's see what you get at the current sensing transformer.
The voltage reading on the MOSFET's indicated that they are not being driven after the backlights go out.

[TimT]

Re: phillips lcd keeps blowing fuse

I believe he wanted a full picture of the inverter board. thats in post 99

[selldoor]

Re: phillips lcd keeps blowing fuse

That suggests they are ok - at least to the point of not being shorted - as I said perhaps budm will comment on the voltages - please post the picture he requested.

[TimT]

Re: phillips lcd keeps blowing fuse

If I set the meter to 200 and test i get 1. only when I set meter to highest ohm setting do I get a reading.

[vinceroger69]

Re: phillips lcd keeps blowing fuse

good guide for testing mosets out of circuit
http://www.4qdtec.com/mostest.html

[selldoor]

Re: phillips lcd keeps blowing fuse

here are my results. tested transformers with power off, meter set to 2000 ohms using the + - probes on the pins all were 958. reversed probes all same 958.

selldoor the Mosfets are 50N04. tested powerd on - grounded to chassis. meter set to 200 dcv
results are in picture. thanks everyone!

OK Did all the transformers test the same?

I was expecting this test
Mosfets

If you have a manual range multimeter, set it to 200 ohms (two hundred). This is for 3 pin ICs only. You can test a mosfet (Q, IC designation) "in circuit" by (power off and unplugged)

a) black on pin 1- red on pin 2 - record ohms
b) black on pin 1- red on pin 3 - record ohms
c) black on pin 2- red on pin 3 - record ohms

If any reading is less than 30 ohms you might have shorted mosfet. Remove from circuit and repeat the tests to verify.

So I dont really know what to make of the voltages - perhaps Budm will comment.

Can you do apicture of the full boards as he requested - I tried to piece them together but dont think they overlap.

[TimT]

Re: phillips lcd keeps blowing fuse

here are my results. tested transformers with power off, meter set to 2000 ohms using the + - probes on the pins all were 958. reversed probes all same 958.

selldoor the Mosfets are 50N04. tested powerd on - grounded to chassis. meter set to 200 dcv
results are in picture. thanks everyone!

[budm]

Re: phillips lcd keeps blowing fuse

OK, you have all the correct signal and voltages, so check the transformer resistance will be the next test per post 96.

[TimT]

Re: phillips lcd keeps blowing fuse

sorry Budm when you posted this I had to check... it is a 10a fuse with 24v at both ends. I was going off my memory and it's failing me...

[budm]

Re: phillips lcd keeps blowing fuse

That white fuse is fed by the 24V power supply, and you are reading 10V, that does not sound right to me. You can see that the fuse is connected to those red wires for the 24v feeding.

[TimT]

Re: phillips lcd keeps blowing fuse

MisterD When testing all boards are bolted back down. selldoor the SMF near connector is a 10A fuse I tested it right at 10v. but ill need to recheck the rating. I cant remember the correct voltage but 10v is close.
pulled and cleaned inverter but no luck. as far as i know nothing has been replace on this board. power board is " new " from Encompass parts. budm no brownish color at inverter contacts looked clean.

[MisterD]

Re: phillips lcd keeps blowing fuse

As I posted in Post # 93, The Inverter Board has some mounting screws missing as I can see in the picture, these circuit boards need all the screws in place and tightened down to make a ground connection, please answer my question, did you install all of these screws and tighten them down? did you make sure every circuit board has all the screws and that they are all tightened down? please reply back to let us know. Thanks.

[budm]

Re: phillips lcd keeps blowing fuse

I saw those pictures in post 92, but I can figure it out a little better if i get to see the whole board also, I can see on small current sensing transformer on the board.

[selldoor]

Re: phillips lcd keeps blowing fuse

I am off to bed he has posted pics of the inverter board but has had to split into 4 in post92

There is one white fuse that I can see in pic 1 That should be tested.

The inverters are HS482 TM10BS I cant see any but the tm series seem to have the secondaries along one side - see pic.
Meter on ohms 2000 test S1>S2 and S3>S4 for each transformer and post results.
There are quite a lot of Mosfets (Might be 50N04 s )on the board - Q designation and they should be tested also.

[budm]

Re: phillips lcd keeps blowing fuse

OK, the 3v is = Backlights on, and that signal is correct. So now we need to find out why the lamps turn off even though you do have the necessary voltage (24vdc) and the BL_ON signals.
The problem can be bad caps (black electrolytics caps), transformers, lamps, bad connection on the board fingers that make contact with lamps.
I would carefully remove the board and clean the contacts pads real well on the inverter board fingers, also look real close at all the sockets where the board fingers are plugged into, see if there is any sign of heat (plastic housing has brownish color).
Can I also see the whole pictures of the inverter board?

[TimT]

Re: phillips lcd keeps blowing fuse

sorry, this does go into standby mode.. plugged in there is a " tick " but does not power up untill power button is pressed. more pictures

[MisterD]

Re: phillips lcd keeps blowing fuse

I noticed in your pictures of the inverter board that some of the mounting screws are missing, all of the screws must be in place and tightened to ensure a good ground connection from the board to the chassis, this can cause this type of problem. you should make sure all circuit boards have all the mounting screws in place and are snugged down tight. Also it appears that there is something hanging off where the SMF (F1) is mounted to the board, has this fuse been replaced? make sure that is not something shorting to another connection on the board, I believe I saw a previous post about the voltage readings being the same on both sides of this fuse, maybe you should do a continuity check by measuring resistance on this fuse with the meter in both directions. set your meter to ohms on 200 scale. just 200 Not 200k or 200m, just 200 ohms.

[TimT]

Re: phillips lcd keeps blowing fuse

When I plug this TV in it automatically starts up..no stand by. not shure if thats normal for this TV. I can turn it off with the power button I think that may put it in stand by?

when plugged in I hear the " click " from power board. bl SW is 0 then in about 3 seconds it jumps to 2.99 to 3.00v " this is when the backlight kicks in for a split second " it stays at 3v untill I turn the TV off with power button then bl SW is back to 0. I can turn it pack on with power button with the same results.

here are 3 pictures of inverter board. I will post another picture of the other board. and a picture of the way I tested this. Thanks for your help! on the picture labeled connect the connector 4p is getting 1.6v if i remember correctly.

[budm]

Re: phillips lcd keeps blowing fuse

OK, this TV uses:
PWM-SEL pin for lamp brightness control, it is being used by this TV.
BL-ADJ is the analog signal control for the lamp brightness, and it is not being used.
BL-SW is the same as BL_ON. You need to monitor this test point when the TV is plugged in but the power switch is not activated. Then hit the power switch and see if the voltage at this point changes state.
I believe you are getting the correct signal (3V as you had indicated).
I need to see good close up of the inverter board/s.