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Laptop LCD repair. INVERTER bad...

Inverter has been confirmed bad. I don't have any output from it.

What usualy go bad with them ? Transfo , caps ?

Is it a kind of switching power supply ?

Tks for you help

Ben wrote:

I have a high voltage probe. What should be the voltage ~ ? > > Is a meter in AC mode (1kV) can see something or is too high ? > > I also suspect that the BL taht I changed was maybe bad. Near the contact > pin on one side , I saw a very small piece of glass remove. That is why I > want to confirm the Inverter before sending the BL for replacement. > > Tks for your help.... > > >> Ben wrote: >>> Hi , >>> >>> Having a laptop with a suspected bad backlight or Inverter. >>> >>> I had changed the BL but still no display. Can see the image on the >>> screen with a flashlight but the BL doesn't lit. >>> >>> How can I confirm if the Inverter is OK ? >>> >>> What is the voltage that I should read at the BL input ? >>> >>> I have a scope if required. >>> >>> Tks... >>> >>> >> If you changed the backlight, what's left besides the inverter? >> I'm gonna guess that the liklihood of an inverter failure is >> MUCH greater than the liklihood of failed logic driving it. >> Unless you have access to a high voltage probe, the backlight >> voltage will be well in excess of the rating on most normal scope probes. >> And if the new backlight is not lit, you can suspect that >> the voltage ain't present. You can wave your scope probe around >> over the backlight inverter transformer and tell if it's running. >> There's often a cap in series with the backlight that can go open. >> There's sometimes a fuse on the inverter board. Sometimes, they >> go open for no reason. >> mike >> >> -- >> Return address is VALID! >> Bunch-O-Stuff Forsale Here: >>
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> >

Short answer is that I don't know. I expect the striking voltage is gonna be in the range of 1500V. But that's not what you're gonna see on a meter. You're gonna need a scope high voltage probe with enough bandwidth to see the transient. And depending on the probe, it's gonna load the circuit. And if the secondary is not isolated, you run the risk of blowing up the inverter or the scope with the ground loop. Just too many unknowns to predict. First thing to do is see if the inverter is even running. You can probe the primary side with the scope. Or just wave the probe in the air near the transformer.

--
Return address is VALID!
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Reply to
Max
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Oddly enough the fuses like to blow for no reason on these things. I've also had problems with the ceramic output caps. If all else fails you could always buy one of those CCFL PC light kits. They are usually about $15 and you get an inverter and 2 CCFL tubes.

Mike

Reply to
Michael Kennedy

In my experience, FET's and picofuses. As Michael has said, often the picofuses go for no reason - replace 'em and you're often back in business.

Yes. The step-up variety.

Reply to
JW

Anyone ever fix one of the Sony inverters? Tokin S405-b001-z1-0 ??? Rather hard to tell what's what.

Reply to
rb

"rb" wrote in news:4674590d$0$7999$ snipped-for-privacy@roadrunner.com:

Can you find a datasheet on the inverter IC? They usually have a circuit that's close to the end product.

--
Jim Yanik
jyanik
at
kua.net
Reply to
Jim Yanik

Haven't tried that,will give it a try, thanks Jim

Reply to
rb

I've also seen the switching transformers on laptop inverters internally short. Usually this results in an inverter which runs (badly) but overheats the drive IC(s) and causes them to shut down within seconds.

Only way to test these suckers is by isolating each transformer in turn, on most inverters this will result in a shutdown but there will be a brief burst of light from the tubes connected to the good transformers.

The other slightly more annoying failure mode is for one of the drive transistors to short under load. Here, the test is to measure the temperature of the transistor pairs, the bad ones will get MUCH hotter than their neighbours.

In either case, always replace the primary smoothing capacitors even if they look OK, as the latter failure mode often results from dried up caps.

Regards, -A

Reply to
conundrum

Is there any capacitor "built-in" inside the secondary of the transfo ?

I'm trying to mesure the impedance and it looks open.

Reply to
Max

"Max" wrote in news:f56f71$132$ snipped-for-privacy@dns3.cae.ca:

I doubt it.

--
Jim Yanik
jyanik
at
kua.net
Reply to
Jim Yanik

might be because you are measuring the wrong pins? end one will measure around 200-1000 ohms to the other.

Also check those transistors.

regards, -A

Reply to
conundrum

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