820-00138-A Backlight IC

[lctrbrt]

Hi ✌️😁


Have a A1398 / 820-00138-A with no backlight.
Unfortunately I realized to late that the boardview file I have doesnt match.

Because that I unfortunately soldered the wrong IC(LP8549B1SP-03) and it burned. Now theres a small hole in the board and there are 2 pins (8: PPVOUT_BLKT_FB2 & 9: ISNS_LCDBKLT_N) missing.

I think I will get it with jumpers but can somebody tell how the right IC is named?

Thanks in advance and a nice weekend for you all 😃

[dellxps15]

Re: 820-00138-A Backlight IC

schematic and boardview here :
https://www.badcaps.net/forum/showth...ight=820-00138

maybe u soldered it wrong

post picture of the damaged area after ic removed and cleaned

[lctrbrt]

Re: 820-00138-A Backlight IC

That was the *.brd I was using and instead of ordering and soldering the IC U7701 I stupidly ordered the U7750 and soldered it.

Dont have a camera on my microscope but will try it with an usb microscope tomorrow if I aint forget it at home 😅

Many thanks ✌️

[dellxps15]

Re: 820-00138-A Backlight IC

u can try with a decent light source and good phone camera

[lctrbrt]

Re: 820-00138-A Backlight IC

I dont have a camera here but didn't forget the USB-Microscope which is anything else than decent

Here is a picture but not really good one. There you see the small 'hole' at pins 8-9.

Also there are connections in the board; 2 contacts and I think that they where connected to the ripped/burned pads so it should be possible to jumper from there(I hope )

Here's the picture and I also figured out that I have the right driver IC which should be called: 'LP8548B1SQ_-4'

[dellxps15]

Re: 820-00138-A Backlight IC

i cant say so much from that picture, but check red circled zone... why that strange color? was water damage corrotion?

after clean all the zone carefully expecially those 2 pins check for connection from :

pin 8 probe is 509
pin 9 probe is 88

on boardview do short and probe the value. ull see one spot near u7701

check if that pin is still alive or u need a jumper wire.

before put a new chip check if any shorted component.

that ic boost voltage from 12.5 to 55 volt

[lctrbrt]

Re: 820-00138-A Backlight IC

Unfortunately I dont have any history for that device but I bet there was a prior repair because there was flux all over that area not cleaned very well and I also didnt not clean it before taking picture so it should be flux. I dont see any corrosion or anything in that area under the microscope.

The connection in that hole where I think its pin 9 has a reading of 0.424 and the one under which I consider pin 8 has a reading of 0.563 so I guess my assumption is wrong and I should put UV-solder-mask on that whole and jumper pins from other parts.

Really a big thank you for your help, I appreciate that

[dellxps15]

Re: 820-00138-A Backlight IC

0.424 in diode mode from gnd to pins ?

check in diode mode from that line to pin if they are still working...
red line from A to B is it connected ? 0000 should output in diode or beep

same for green line....

for 0.424 lets see what u mean if pin is shorted or what...

edit: ok so some of the staff on board was flux. but pin 8-9 are melted together ? use some solder wick with flux, clean the board properly... are still pin 8-9 together or they are individual ?

[lctrbrt]

Re: 820-00138-A Backlight IC

Hi,

sry had to assemble some iPhones so I couldn't answer on Saturday.


The 2 Pins aren't shorted it looks only because of the bad picture quality. If i measure them the DMM shows OL.

I measured up the red line from your picture but somehow there is only continuous at the other side of that cap than your picture shows.

Here's a picture with diode mode readings from that pin '8' and where I think the line goes. I do a next one for pin9.

[lctrbrt]

Re: 820-00138-A Backlight IC

Here's the other picture with line from pin 9

[dellxps15]

Re: 820-00138-A Backlight IC

you are making some confusion. for short u have to probe in diode mode: black on gnd ( metal of usb or any other gnd spot on the board) and red on pin 8 and read the value. then gnd and pin 9 and read the value.

next if no short ( value of diode mode over 010. [001 002 is short])

probe in diode mode black on A and red to B(pin8).. if 001 or 002 then pin 8 still working
probe in diode mode black on C (pin 9) and red on D if 001 002 then pin 9 is working.

that's first step

next step is probe all u7701 pins in diode black on gnd and red on each pin reading value and looking for short. read each pin value and check if shorted or not ( if short check if its not gnd on schematic.

hope that help

[lctrbrt]

Re: 820-00138-A Backlight IC

Sry for that. I not only reversed the probes, I also used the wrong ones. The tips where to fat so shame on me����*♂️

Short-Test:

If I put red on pin8 and black on Gnd I got a reading OL
Then if I put black on pin9 I got 0.000

But I dont understand why at the second measurement I supposed to put black on Pin9? Sry if thats a dumb question but if I test continuity shouldn't I also place red on pin9 and black on ground?

Somehow, the tut's where I read saying that when probing in diode mode the probes should reversed that why I'm a little bit confused.

[dellxps15]

Re: 820-00138-A Backlight IC

in diode mode i never used red on gnd and black for probe, for me it's the same red or black, the resulted value is walways he same.

1 st measurement is to see if short.
2nd measurement is fot see if pin 9 ior pin 8 s still a pin with contact to the origin or is just isolated after the burn

example:
pin 9 is related to ppvout backlignt fb2 ... that signal comes from somerwhere on the board... track is till working or is melted after the burn? that's why second measurement as described in post #6 and #11

[lctrbrt]

Re: 820-00138-A Backlight IC

Okay, I'll have a look tomorrow.

Maybe my multimeter sucks but I extra take a expensive one, the Amprobe Hexagon 340 but I'll test tomorrow with another one if the readings are the same.


Again I really have to thank for your patience and help. If you sometimes in Berlin then tell me, I'll thank you personally

[lctrbrt]

Re: 820-00138-A Backlight IC

Hi again,

so yesterday evening I reread/-watched the tutorials from Jessa Jones and Louis Rossmann and there they told that if measuring in diodemode that the majority is using red on GND and black on the Part/pad which is to test and thats why I used to do it this way.

Beside that I took my cheap 5 bucks DMM and made a list with all readings from the pins. The other(hexagon 340A) one also works but there are the numbers slightly different(less).

Here's the list:

	
Pin1	 OL	  | Pin13	OL
Pin2	 OL	  | Pin14	OL
Pin3	 001	  | Pin15	OL
Pin4	 OL	  | Pin16	OL
Pin5	 416	  | Pin17	663
Pin6	 416	  | Pin18	416
Pin7	 001	  | Pin19	OL
Pin8	 658	  | Pin20	OL
Pin9	 461	  | Pin21	OL
Pin10  462	  | Pin22	001
Pin11  OL	  | Pin23	001
Pin12  832	  | Pin24	001

If measuring the pins would it be better with LCD connected or is it ok without it?

[dellxps15]

Re: 820-00138-A Backlight IC

Hi again,

so yesterday evening I reread/-watched the tutorials from Jessa Jones and Louis Rossmann and there they told that if measuring in diodemode that the majority is using red on GND and black on the Part/pad which is to test and thats why I used to do it this way.

Beside that I took my cheap 5 bucks DMM and made a list with all readings from the pins. The other(hexagon 340A) one also works but there are the numbers slightly different(less).

Here's the list:

	
Pin1	 OL	  | Pin13	OL
Pin2	 OL	  | Pin14	OL
Pin3	 001	  | Pin15	OL
Pin4	 OL	  | Pin16	OL
Pin5	 416	  | Pin17	663
Pin6	 416	  | Pin18	416
Pin7	 001	  | Pin19	OL
Pin8	 658	  | Pin20	OL
Pin9	 461	  | Pin21	OL
Pin10  462	  | Pin22	001
Pin11  OL	  | Pin23	001
Pin12  832	  | Pin24	001

If measuring the pins would it be better with LCD connected or is it ok without it?

001 = short.

on schematics pin 3,7,22,23,24 are GND. so all pins and board is ok.

solder new chip on it and see if it works.

[lctrbrt]

Re: 820-00138-A Backlight IC

It didn't work😅

I send it to somebody else and guess I've to learn a little bit more but anyways, many thanks for our help I'll surely will annoy you in future

[dellxps15]

Re: 820-00138-A Backlight IC

lets hope they will fix it cheers

[niharkanti]

Re: 820-00138-A Backlight IC

Hi,

sry had to assemble some iPhones so I couldn't answer on Saturday.


The 2 Pins aren't shorted it looks only because of the bad picture quality. If i measure them the DMM shows OL.

I measured up the red line from your picture but somehow there is only continuous at the other side of that cap than your picture shows.

Here's a picture with diode mode readings from that pin '8' and where I think the line goes. I do a next one for pin9.

SIR , I WANT TO KNOW THIS U7701 IC PIN - 7/8/9/10/11/12 SIDE 4 RESISTOR PRESENT , PLEASE GIVE ME THIS RESISTOR VALUE THE 4 RESISTOR . PLEASE HELP ME SIR.

[mon2]

Re: 820-00138-A Backlight IC

R7757 = 0 ohms 5% 0201 size
R7758 = 0 ohms 5% 0201 size

R7760 = 2k4 5% 0201 size
R7761 = 2k4 5% 0201 size