Electronics Repair (sci.electronics.repair) Discussion of repairing electronic equipment. Topics include requests for assistance, where to obtain servicing information and parts, techniques for diagnosis and repair, and annecdotes about success, failures and problems.

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Max Max is offline
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Default 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....


"mike" wrote in message
news:LZobi.5056$3Q4.1247@trnddc05...
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!
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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!
Bunch-O-Stuff Forsale He
http://mike.liveline.de/sale.html


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Default Laptop LCD repair. INVERTER bad...


"Max" wrote in message
...
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



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


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JW JW is offline
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Default Laptop LCD repair. INVERTER bad...

On Fri, 15 Jun 2007 11:51:30 -0400 "Max" wrote in
Message id: :

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

What usualy go bad with them ? Transfo , caps ?


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.

Is it a kind of switching power supply ?


Yes. The step-up variety.
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rb rb is offline
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Default Laptop LCD repair. INVERTER bad...


"JW" wrote in message
...
On Fri, 15 Jun 2007 11:51:30 -0400 "Max" wrote in
Message id: :

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

What usualy go bad with them ? Transfo , caps ?


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.

Is it a kind of switching power supply ?


Yes. The step-up variety.



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


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Default Laptop LCD repair. INVERTER bad...

"rb" wrote in
:


"JW" wrote in message
...
On Fri, 15 Jun 2007 11:51:30 -0400 "Max" wrote in
Message id: :

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

What usualy go bad with them ? Transfo , caps ?


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.

Is it a kind of switching power supply ?


Yes. The step-up variety.



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




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


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Default Laptop LCD repair. INVERTER bad...


"Jim Yanik" wrote in message
...
"rb" wrote in
:


"JW" wrote in message
...
On Fri, 15 Jun 2007 11:51:30 -0400 "Max" wrote in
Message id: :

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

What usualy go bad with them ? Transfo , caps ?

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.

Is it a kind of switching power supply ?

Yes. The step-up variety.



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




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


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


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Default Laptop LCD repair. INVERTER bad...

On Jun 17, 7:26 pm, "rb" wrote:
"Jim Yanik" wrote in message

...



"rb" wrote in
:


"JW" wrote in message
. ..
On Fri, 15 Jun 2007 11:51:30 -0400 "Max" wrote in
Message id: :


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


What usualy go bad with them ? Transfo , caps ?


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.


Is it a kind of switching power supply ?


Yes. The step-up variety.


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


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


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




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

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Default Laptop LCD repair. INVERTER bad...

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

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



"conundrum" wrote in message
oups.com...
On Jun 17, 7:26 pm, "rb" wrote:
"Jim Yanik" wrote in message

...



"rb" wrote in
:


"JW" wrote in message
. ..
On Fri, 15 Jun 2007 11:51:30 -0400 "Max" wrote
in
Message id: :


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


What usualy go bad with them ? Transfo , caps ?


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.


Is it a kind of switching power supply ?


Yes. The step-up variety.


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


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


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




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



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Default Laptop LCD repair. INVERTER bad...

"Max" wrote in :

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

I doubt it.



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


--
Jim Yanik
jyanik
at
kua.net
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Default Laptop LCD repair. INVERTER bad...

On Jun 18, 9:09 pm, Jim Yanik wrote:
"Max" wrote :

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


I doubt it.



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


--
Jim Yanik
jyanik
at
kua.net



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

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