Badcaps.net Forum
Go Back   Badcaps Forums > Troubleshooting Hardware & Devices and Electronics Theory > Troubleshooting Power Supplies and Power Supply Design
Register FAQ Calendar Search Today's Posts Mark Forums Read

 
Thread Tools Display Modes
Old 01-31-2017, 12:00 PM   #1
Dannyx
CertifiedAxhole
 
Dannyx's Avatar
 
Join Date: Aug 2016
City & State: Constanta
My Country: Romania
Line Voltage: 230VAC 50Hz
I'm a: Hardcore Geek
Posts: 3,277
Question Dell laptop LA90PE0-01 charger repair

Good day folks. This may seem like a pointless thing to try and repair, but I've got a dead original DELL slim charger which I'm trying to fix and I figured it might be something others have stumbled upon, given that DELL is a fairly popular brand which others are likely to own. The model is LA90PE0-01 and the issue is simple: it doesn't output anything at all. I took it apart and after hours of fighting with that white silastic sh!t they felt the need to "paint" the whole board with, I eventually uncovered the board enough to take some measurement: I get around 325v on the main cap and 15 to 20v on pin 1 of the IC (goes up and down). This is where it gets slightly complicated and over my head: the IC is a LTA804N which controls BOTH the PFC circuit and the main switching one. I could not find too much about this thing, however I did find one source which says it's identical to TEA1751 (datasheet here). I was also lucky enough to find the schematic for the whole adapter here. Following along with the schematic and the pinout as best as I could, I do get some volts on pin 1 VCC of the IC, but nothing else elsewhere...I don't know if it's even pulsing those FETs on and off, because I don't have an oscilloscope to measure the gates The overcomplicated nature of that IC is also annoying. Resistors seem fine, except for one of the 1504 (1.5 megOhm, bottom left of schematic, which seems to be reading too low - only 800kohms). Already replaced C054, since it's in parallel with the VCC pin of the IC which sometimes causes issues, but it didn't change anything....any help would be greatly appreciated
Attached Images
File Type: jpg 20170131_173218.jpg (827.4 KB, 222 views)
File Type: jpg 20170131_173005.jpg (713.5 KB, 256 views)
File Type: jpg 20170131_173014.jpg (805.8 KB, 311 views)
__________________
Wattevah...
Dannyx is offline   Reply With Quote
Old 01-31-2017, 12:06 PM   #2
Dannyx
CertifiedAxhole
 
Dannyx's Avatar
 
Join Date: Aug 2016
City & State: Constanta
My Country: Romania
Line Voltage: 230VAC 50Hz
I'm a: Hardcore Geek
Posts: 3,277
Default Re: Dell laptop LA90PE0-01 charger repair

Also, I've just read that some other guy (from Poland I believe) was having the same issue, but when he tried probing the primary of the transformer (the one in the top right in my pictures), the power suddenly came on, so it could also be a bad joint somewhere which perhaps makes contact when he applied slight pressure with the probes.....haven't tried reflowing the thing yet....that would be one hell of a fix
Dannyx is offline   Reply With Quote
Old 01-31-2017, 04:13 PM   #3
cpt.charlie
Badcaps Veteran
 
Join Date: Sep 2013
City & State: Torrelavega
My Country: Spain
Line Voltage: 230VAC 50Hz
I'm a: Knowledge Seeker
Posts: 255
Default Re: Dell laptop LA90PE0-01 charger repair

Do you have HV at pin 16?

Last edited by cpt.charlie; 01-31-2017 at 04:19 PM..
cpt.charlie is offline   Reply With Quote
Old 02-01-2017, 02:25 AM   #4
Dannyx
CertifiedAxhole
 
Dannyx's Avatar
 
Join Date: Aug 2016
City & State: Constanta
My Country: Romania
Line Voltage: 230VAC 50Hz
I'm a: Hardcore Geek
Posts: 3,277
Default Re: Dell laptop LA90PE0-01 charger repair

Quote:
Originally Posted by cpt.charlie View Post
Do you have HV at pin 16?
I get 326v on pin 16

Last edited by Dannyx; 02-01-2017 at 03:31 AM.. Reason: Correction
Dannyx is offline   Reply With Quote
Old 02-01-2017, 04:32 AM   #5
Dannyx
CertifiedAxhole
 
Dannyx's Avatar
 
Join Date: Aug 2016
City & State: Constanta
My Country: Romania
Line Voltage: 230VAC 50Hz
I'm a: Hardcore Geek
Posts: 3,277
Default Re: Dell laptop LA90PE0-01 charger repair

Also, I get 3.5v on pin 7 which is the VINSENSE pin. According to the datasheet for the TEA chip, that should be enough to start it.
Dannyx is offline   Reply With Quote
Old 02-01-2017, 07:00 AM   #6
CapLeaker
Leaking Member
 
CapLeaker's Avatar
 
Join Date: Dec 2014
City & State: Atlantic Canada
My Country: Canada
Line Voltage: Ground, 0Hz
I'm a: Hobbyist Tech
Posts: 5,219
Default Re: Dell laptop LA90PE0-01 charger repair

Resistors when they fail don't go 50% lower in value. They always go higher or open. So put that 1.5 M Ohm resistor back in. Could very well be that there is a bad solder joint and power isn't getting there where it is needed. Had bad solder joints on transformers before. I've also seen my share of a broken leg (broken flush on the top side of PCB) filter inductors even so they were glued. You would have to examen things.

You said you do get some volts on pin one of the TEA1751. What exactly do you get? Look at the schematic. There is a startup cap 35V 47uF.
CapLeaker is offline   Reply With Quote
Old 02-01-2017, 08:19 AM   #7
Dannyx
CertifiedAxhole
 
Dannyx's Avatar
 
Join Date: Aug 2016
City & State: Constanta
My Country: Romania
Line Voltage: 230VAC 50Hz
I'm a: Hardcore Geek
Posts: 3,277
Default Re: Dell laptop LA90PE0-01 charger repair

Quote:
Originally Posted by CapLeaker View Post
Resistors when they fail don't go 50% lower in value. They always go higher or open. So put that 1.5 M Ohm resistor back in. Could very well be that there is a bad solder joint and power isn't getting there where it is needed. Had bad solder joints on transformers before. I've also seen my share of a broken leg (broken flush on the top side of PCB) filter inductors even so they were glued. You would have to examen things.

You said you do get some volts on pin one of the TEA1751. What exactly do you get? Look at the schematic. There is a startup cap 35V 47uF.
I've just fixed it The issue ? A 0 ohm "jumper" resistor had gone open circuit. It's the one next to the optocoupler in the schematic (to the right of the main IC). I was following the traces for the optocoupler according to the schematic, until I reached that 0 Ohm jumper where continuity suddenly stopped. I pulled it out, measured it and indeed it read 2 megOhms - WAY above the intended value. I replaced it with an ordinary piece of wire and tried it out - works perfectly. Sadly, I was too excited about my victory to take some measurements and post them here to hopefully help other chaps who might run into this issue, but bottom line is: replace the small cap for the VCC pin of the IC and check all resistors, starting with that 0 ohm one. Cheers
Dannyx is offline   Reply With Quote
Old 02-01-2017, 09:00 AM   #8
sam_sam_sam
Badcaps Veteran
 
Join Date: Jul 2011
City & State: Some times Sunny Jacksonville FL
My Country: USA
Line Voltage: 120 Volts 60 HZ
I'm a: Knowledge Seeker
Posts: 3,656
Default Re: Dell laptop LA90PE0-01 charger repair

I would put in one those resettable fuses
I will post a photo of one later
__________________
9 PC LCD Monitor
6 LCD Flat Screen TV
30 Desk Top Switching Power Supply
10 Battery Charger Switching Power Supply for Power Tool
6 18v Lithium Battery Power Boards for Tool Battery Packs
1 XBox 360 Switching Power Supply and M Board
25 Servo Drives 220/460 3 Phase
6 De-soldering Station Switching Power Supply 1 Power Supply
1 Dell Mother Board
15 Computer Power Supply
1 HP Printer Supply & Control Board * lighting finished it *


These two repairs where found with a ESR meter...> Temp at 50*F then at 90*F the ESR reading more than 10%

1 Over Head Crane Current Sensing Board ( VFD Failure Five Years Later )
2 Hem Saw Computer Stack Board

All of these had CAPs POOF
All of the mosfet that are taken out by bad caps
sam_sam_sam is offline   Reply With Quote
Old 02-01-2017, 11:41 AM   #9
CapLeaker
Leaking Member
 
CapLeaker's Avatar
 
Join Date: Dec 2014
City & State: Atlantic Canada
My Country: Canada
Line Voltage: Ground, 0Hz
I'm a: Hobbyist Tech
Posts: 5,219
Default Re: Dell laptop LA90PE0-01 charger repair

Yeah... I had another look at the schematic. If that 0 ohm resistor went open or high in value, it will sour your day quickly. As sam_sam_sam stated, they used that 0 ohm resistor as a fuse.
CapLeaker is offline   Reply With Quote
Old 02-01-2017, 12:18 PM   #10
Dannyx
CertifiedAxhole
 
Dannyx's Avatar
 
Join Date: Aug 2016
City & State: Constanta
My Country: Romania
Line Voltage: 230VAC 50Hz
I'm a: Hardcore Geek
Posts: 3,277
Default Re: Dell laptop LA90PE0-01 charger repair

Quote:
Originally Posted by CapLeaker View Post
Yeah... I had another look at the schematic. If that 0 ohm resistor went open or high in value, it will sour your day quickly. As sam_sam_sam stated, they used that 0 ohm resistor as a fuse.
Ok, but (so far at least), nothing's really complaining...it might fail again sooner or later though. What exactly is that "fuse" protecting and what was its cause of failure ? I see it's in series with the AUX winding, but I couldn't find any shorts - none at all...
Dannyx is offline   Reply With Quote
Old 02-01-2017, 12:50 PM   #11
budm
Badcaps Veteran
 
budm's Avatar
 
Join Date: Feb 2010
City & State: S.F. Bay area
My Country: USA
Line Voltage: 120V 60Hz
I'm a: Knowledge Seeker
Posts: 39,206
Default Re: Dell laptop LA90PE0-01 charger repair

http://www.badcaps.net/forum/attachm...1&d=1485884098
Can you show us where that '0' Ohms resistor on the is?
__________________
Never stop learning
Basic LCD TV and Monitor troubleshooting guides.
http://www.badcaps.net/forum/showthr...956#post305956

Voltage Regulator (LDO) testing:
http://www.badcaps.net/forum/showthr...999#post300999

Inverter testing using old CFL:
http://www.badcaps.net/forum/showthr...er+testing+cfl

Tear down pictures : Hit the ">" Show Albums and stories" on the left side
http://s807.photobucket.com/user/budm/library/

TV Factory reset codes listing:
http://www.badcaps.net/forum/showthread.php?t=24809
budm is offline   Reply With Quote
Old 02-01-2017, 12:54 PM   #12
Dannyx
CertifiedAxhole
 
Dannyx's Avatar
 
Join Date: Aug 2016
City & State: Constanta
My Country: Romania
Line Voltage: 230VAC 50Hz
I'm a: Hardcore Geek
Posts: 3,277
Default Re: Dell laptop LA90PE0-01 charger repair

Quote:
Originally Posted by budm View Post
http://www.badcaps.net/forum/attachm...1&d=1485884098
Can you show us where that '0' Ohms resistor on the is?
Above the top-right corner of the PFC inductor (that's the yellow square at the bottom in the picture you linked), there's a hole - you can see a "0" right above that hole, placed vertically in the picture. Sorry, I didn't feel like downloading the pic again and marking it in MS Paint
Dannyx is offline   Reply With Quote
Old 02-01-2017, 01:11 PM   #13
budm
Badcaps Veteran
 
budm's Avatar
 
Join Date: Feb 2010
City & State: S.F. Bay area
My Country: USA
Line Voltage: 120V 60Hz
I'm a: Knowledge Seeker
Posts: 39,206
Default Re: Dell laptop LA90PE0-01 charger repair

OK, I see that now.
budm is offline   Reply With Quote
Old 02-02-2017, 05:24 AM   #14
sam_sam_sam
Badcaps Veteran
 
Join Date: Jul 2011
City & State: Some times Sunny Jacksonville FL
My Country: USA
Line Voltage: 120 Volts 60 HZ
I'm a: Knowledge Seeker
Posts: 3,656
Default Re: Dell laptop LA90PE0-01 charger repair

Quote:
Originally Posted by sam_sam_sam View Post
I would put in one those resettable fuses
I will post a photo of one later
This is the kind of fuse that I was taking about
Polyswitch Resettable Fuse 170mA 120V 2 Pin bel0017RM PTC | eBay

For some reason the link doesn't work

Last edited by sam_sam_sam; 02-02-2017 at 05:26 AM..
sam_sam_sam is offline   Reply With Quote
Old 02-02-2017, 09:08 PM   #15
delaware74b
Badcaps Veteran
 
delaware74b's Avatar
 
Join Date: Apr 2009
City & State: Delaware
My Country: USA
Line Voltage: 480VAC 60Hz or Less
I'm a: Knowledge Seeker
Posts: 597
Default Re: Dell laptop LA90PE0-01 charger repair

Did you reflow the broken solder joint I circled on the back of the board?
Attached Images
File Type: jpg 20170131_173014.jpg (1.41 MB, 168 views)
__________________
Stupidity should be a crime, especially for drivers. I have NO patience for them.
delaware74b is offline   Reply With Quote
Old 02-03-2017, 02:01 AM   #16
Dannyx
CertifiedAxhole
 
Dannyx's Avatar
 
Join Date: Aug 2016
City & State: Constanta
My Country: Romania
Line Voltage: 230VAC 50Hz
I'm a: Hardcore Geek
Posts: 3,277
Default Re: Dell laptop LA90PE0-01 charger repair

Quote:
Originally Posted by delaware74b View Post
Did you reflow the broken solder joint I circled on the back of the board?
Yes I have. I've actually reflown MANY other joints for good measure
Dannyx is offline   Reply With Quote
Old 01-26-2019, 06:22 PM   #17
eckibear
New Member
 
Join Date: Jan 2019
City & State: Hesse
My Country: Germany
I'm a: Knowledge Seeker
Posts: 1
Default Re: Dell laptop LA90PE0-01 charger repair

Hi all,

I found this blog very helpfull, thank you guys!
I've encountered yet another zero-Ohm "fuse" in my power supply of this type. This 0R resistor does not appear in the schematic. It is placed between the upper winding of Transformer T050 and the anode side of diode "JSW" & R-52k3, on the very top of the schematic. It is marked up by the yellow circle below (the red circle shows the zero Ohm Resistor/"fuse" discussed above).
BTW.: My supply was way more filled up with the white silicon putty, hardly any area was left open. I guess it had been very cheap on that day of manufacture.

Cheers,
eckibear
Attached Images
File Type: jpg Inside_power_supply_3.jpg (2.16 MB, 109 views)
eckibear is offline   Reply With Quote
Old 10-30-2019, 06:09 AM   #18
MPFI
New Member
 
Join Date: Oct 2019
City & State: Buenos Aires
My Country: Argentina
I'm a: Knowledge Seeker
Posts: 3
Default Re: Dell laptop LA90PE0-01 charger repair

I just registered to thank you for the solution. It helped with my DELL charger as well. Done some measurement. I concluded that the chip was good since the PFC was OK, I got 300V no problems. but measuring arund the optocouples ... got lost. I found a 0 jumper opened. Wondering if the boar design, that has two major holes to fit the low profile transformers (on coil and one transformer) just weakened the board and could crack SMD components. Could be the reason for the silastic flood (YES ... I spent a lot of time cleianing this LOL).

Many thanks !!!!
MPFI is offline   Reply With Quote
Old 10-30-2019, 10:32 AM   #19
stj
Great Sage 齊天大聖
 
stj's Avatar
 
Join Date: Dec 2009
City & State: Europe
My Country: some shithole run by Israeli agents
I'm a: Professional Tech
Posts: 26,852
Default Re: Dell laptop LA90PE0-01 charger repair

those resistors are used to pass over other tracks, it's possible the person who designed that forgot to take into account how much current was flowing when they chose the resistors.
stj is offline   Reply With Quote
Old 10-31-2019, 12:46 PM   #20
MPFI
New Member
 
Join Date: Oct 2019
City & State: Buenos Aires
My Country: Argentina
I'm a: Knowledge Seeker
Posts: 3
Default Re: Dell laptop LA90PE0-01 charger repair

Quote:
Originally Posted by stj View Post
those resistors are used to pass over other tracks, it's possible the person who designed that forgot to take into account how much current was flowing when they chose the resistors.
Could be, but in this case are related to the optocoupler cricuitry (output side) I dont tink that the current could be that high.
MPFI is offline   Reply With Quote
Reply

Thread Tools
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off

Forum Jump



Badcaps.net Technical Forums 2003 - 2022
Powered by vBulletin ®
Copyright ©2000 - 2022, Jelsoft Enterprises Ltd.
All times are GMT -6. The time now is 07:21 AM.
Did you find this forum helpful?