phillips lcd keeps blowing fuse

[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

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

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!

[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.

[vinceroger69]

Re: phillips lcd keeps blowing fuse

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

[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.

[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

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

[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

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

I expect something like 0.2~0.5v when lamps are on, and more than a volt if the lamps draw too much current.
I am running out of idea, I am thinking about put the jumper on the two terminals on the left side of that current sensing transformer to see if the lamps will stay on, that will tell us if the lamps shutdown due to too much current or not.

[tom66]

Re: phillips lcd keeps blowing fuse

It's quite possible it's a very short transient causing the controller to shut down, if it's a "dumb" controller.

[budm]

Re: phillips lcd keeps blowing fuse

This current sensing method is about the same as the SAMSUNG/SONY use on the balancer board. They save money on this one by using only one sensing transformer for all the lamps, not like SONY/SAMSUNG that detects each lamp.

[TimT]

Re: phillips lcd keeps blowing fuse

I got a new multimeter today (Klein) so I retested the current senser transformer. when lamps kick in 0175. tested twice. it's Auto Ranging.

[budm]

Re: phillips lcd keeps blowing fuse

Did you try jumping those two pin on the left side of the current sensing transformer yet. If it still does not stay when they are jumped then we can eliminate lamp over current as the cause of the problem and look some where else.

[TimT]

Re: phillips lcd keeps blowing fuse

budm you talking about these two pins?

[budm]

Re: phillips lcd keeps blowing fuse

Yes, that is the primary side of the current sensing transformer, the output winding on the right side feeds the Dual Diode to convert AC to DC for the current feedback.

[TimT]

Re: phillips lcd keeps blowing fuse

no luck with the jumper

[budm]

Re: phillips lcd keeps blowing fuse

Well, that eliminate the over current shutdown problem. Need to look some where else next.

[TimT]

Re: phillips lcd keeps blowing fuse

budm do you think the problem is on the inverter board? or somewere else?