42" Sharp lc42d65u No backlight

[XtraTN]

Hey I just got myself this Sharp LCD TV! Model Number: lc42d65u

It had the blinking green LED problem when turned on. I did the PSU forcing on by holding Channel + and Volume - and plugged in the power cable. Then Once I press the power button the green LED turns on solid (no flickers on the screen), I used a flashlight and I can see the picture on the screen just there no backlight..



I also noticed that if I hook on HDMI, I notice the picture but there doesn't seem to be any sound either.

Measuring the fuse on the inverter board I'm getting 23.7V on both ends of the fuse. Is still an inverter problem?

[tom66]

Re: 42" Sharp lc42d65u No backlight

You have CMO inverter board; check the 0.75A/76V fuse as it is a very common failure.

[ben7]

Re: 42" Sharp lc42d65u No backlight

Measure the resistances of all the inverter transformer high voltage windings. Do this with the Tv off, and/or inverter board unplugged!

Any transformer that reads much different from the others is bad. If you arenot sure about the resistance measurments you got, just list them in a post on here.

[XtraTN]

Re: 42" Sharp lc42d65u No backlight

Ah you're right tom, I didn't even notice the smaller black F1 fuse on the board. I'm getting no continuity through the fuse so I guess its bad.

Where can I get another one of these fuses?

[tom66]

Re: 42" Sharp lc42d65u No backlight

Digikey
http://www.digikey.co.uk/product-det...3CT-ND/2037163

Upgrade 0.75A to 2A to reduce failure rate; 63V rating is suitable for 24V inverter.

[budm]

Re: 42" Sharp lc42d65u No backlight

Another CMO with bad fuse for the PWM IC.

[tom66]

Re: 42" Sharp lc42d65u No backlight

I wonder why they blow, is there a large capacitor on the other side of the fuse creating a large inrush current?

[budm]

Re: 42" Sharp lc42d65u No backlight

I think the fuse they are using is a little is under rated, the inrush current I measure with my FLUKE set to peak detection readout to be about 1.5~2A range. I fixed so many CMO boards with the same blown fuse, I use 2A PICO II fuse and none (>10 units) have come back yet.

[tom66]

Re: 42" Sharp lc42d65u No backlight

I was experimenting with some fast blow fuses in a product I am working on, 800mA/63V SMD 1206, and I blew them up installing AA batteries in my new widget, just 100uF capacitor on input @ 3VDC enough to blow those fuses. Not very tolerant of inrush current, so always use slow blow and over-rated fuses. Luckily failure was obvious in the engineering phase and not production phase, or we would have a lot of customer returns!

[budm]

Re: 42" Sharp lc42d65u No backlight

Good to have meter with peak hold reading with 1mSEC capture time. I also put the UUT on the power cycle ON/OFF for about a week to burn in.

[retiredcaps]

Re: 42" Sharp lc42d65u No backlight

Good to have meter with peak hold reading with 1mSEC capture time.

With respect to the Fluke hand held multimeters, only the Fluke 87 (I, III and V) series have the peak min/max feature.

The 187/189/87IV/89IV/287/289 have fast min/max which can capture transient signal events as short as 250 µs, but with decreased accuracy; only 3-1/2 display digits are allowed.

And yes it is an useful feature to have to detect over voltage protection problems like on an ATX power supply.

[budm]

Re: 42" Sharp lc42d65u No backlight

I use good old reliable Fluke 87 everyday, also has Fluke 189.

[XtraTN]

Re: 42" Sharp lc42d65u No backlight

That did it! Replaced the little fuse and the set came back to life! Thanks guys!!