IBM X31 Inverter failed capacitor identification

[hgg]

Hi,

My IBM X31 laptop screen stopped working after many years of use.   

If I shine a flashlight on the LCD I can see the BIOS text which means that its either the inverter
or the CCFL.  I've measured the output region with the non contact measurement of the UT210E
and it showed no output voltage.  I removed the output capacitor from the inverter and while
it is not short circuit, I can only measure a few pF.  So I assume that it failed open.  The high
voltage transformer looks ok and its not shorted.

Is there anyway to find out the value of the damaged capacitor, in order to replace it?

Thanks.

[wraper]

I can only measure a few pF.  So I assume that it failed open.  The high
voltage transformer looks ok and its not shorted.

It measures as it should, unlikely to be above 10pF nominal. Better check if secondary winding is not open. And had you checked if there was power on the inverter at all?

[hgg]

That's exactly what I measure.  10pF.   
So maybe its something else on the board because the unit has no output.

[hgg]

Ok, the two transformer leads near the output capacitor are open circuit.
Did the little transformer fail?

[hgg]

Anyone that knows how to test these transformers ?

This is what I measure :



Thanks.
 

[brabus]

Last time I had this kind of fault, the inverter was perfectly working. It was not receiving supply from the mainboard, due to an open fuse!
Fuse replaced, et voilà, light again.

Regarding the inverter, I always avoided repairing them. Too much time and effort involved, for such a price: http://www.ebay.com/sch/i.html?_from=R40&_trksid=p2050601.m570.l1313.TR0.TRC0.H0.Xibm+x31+inverte.TRS0&_nkw=ibm+x31+inverter&_sacat=0

[hgg]

First thing I did was to check the fuses.  One next to the connector and one on the inverter board.
Both were fine.  I can buy a new inverter but I want to see if it is easy to find the fault and be %100 sure.

[wraper]

First thing I did was to check the fuses.

You should check the actual voltage. I may be just a lid switch of hall sensor broken or knocked of the board.

[senso]

Or dead CCFL's..

[Flenser]

The screen on my X200 laptop went dark in 2014.
Like the OP I could see the BIOS messages using a torch so I had a good indication it was either the CCFL tube or inverter.
I first purchased a "CCFL Lamp Inverter Tester" on ebay for AU$6.61. The same looking item is going for AU$3.77 today.
This was a pretty cheap way for me to confirm that the CCFL lamp was working OK.

[hgg]

Not a bad idea, thanks I think I will buy one like the following:
http://www.ebay.com/itm/CCFL-Inverter-Tester-LCD-TV-Laptop-Screen-Repair-Backlight-Lamp-Test-MAX-300mm-/280757880616?hash=item415e794728:g:ZXIAAOSwY45UQJo7

670V @ 5mA is not a toy though...

But anyway if someone knows a simple way to test an inverter like the one above, I would be glad to know.
I am more interested in learning new stuff.

[MadTux]

But anyway if someone knows a simple way to test an inverter like the one above, I would be glad to know.
I am more interested in learning new stuff.

Build a 10x divider from 9x 10Meg resistors and the 10Meg input usually found on DMMs in the 100-1000V range. Put DMM in AC mode and hook divider to output of the transformer. Won't give very accurate reading, more like an estimate of  whether the transformer is working or not.

Oscilloscope and spectum analyzer (if you have them  ) are also very handy when working with such things. Just put the scope in maximum sensitivity and use a wire loop antenna to pick up stray fields on the PCB. Spectum analyzer is even more useful, as you can see both frequency and amplitude.

[wraper]

But anyway if someone knows a simple way to test an inverter like the one above, I would be glad to know.
I am more interested in learning new stuff.

Build a 10x divider from 9x 10Meg resistors and the 10Meg input usually found on DMMs in the 100-1000V range. Put DMM in AC mode and hook divider to output of the transformer. Won't give very accurate reading, more like an estimate of  whether the transformer is working or not.

Oscilloscope and spectum analyzer (if you have them  ) are also very handy when working with such things. Just put the scope in maximum sensitivity and use a wire loop antenna to pick up stray fields on the PCB. Spectum analyzer is even more useful, as you can see both frequency and amplitude.

First of all, some load is needed, otherwise protection will kick in and there will be no voltage.
My question still remains the same, is there a power on inverter module? Checking fuses is good, of course, but don't answer this question. Also there should be brightness PWM signal and enable signal. Something like on the picture.

[wraper]

https://www.rom.by/files/MP1015.pdf
Yep, there must be separate enable input.

[hgg]

I get the following readings from the MP1015 CCFL driver:

Pin 1 (Analog Dimming ) : 4.8Vdc
Pin 4 (Burst Mode Dimming ) : 1.3Vdc
Pin 5 (Enable) : 2.7Vdc
Pin 7 (Power Supply Input) : 15.7Vdc

Pin 1 looks too high.  Recommended range is 0V - 1.9V