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#1 |
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![]() Hi,
I have an ASUS ux410u that is no boot no power. I'm trying to find out the issue and I'm seeking for help. I'm not a specialist, I have a background in electronics from engineering schools but nothing more. The good news is that I have another ux410u that is working perfectly, so, I could compare if needed. I've disassembled it and isolated the mainboard of the defective one and made some checks: * the power port is ok, I get 19.4v on the board * After the two first mosfets, I still have 19.4v * Without doing any voltage injection (just the official power adapter), a component is getting super hot: I can feel it with my finger. With alcohool and microscope, it's pretty clear that it is this component. * The hot component is 2N=4a... which seems to be Richtek RT8249C: https://www.richtek.com/assets/produ...8249ABC-02.pdf * For sanity, I tried to find a short around the hot component but no "success". I've made some measurements and have some questions: * my understanding is that RT8249C should do linear output 3.3V on pin 3 and linear output 5V on pin13. My measure are not even close to that. For that chip, I get 19.3V for vin (pin12), ~0.8v for pin 3 (vs expected 3.3v) and roughly 0V everywhere else. Pin 13 (5V) is giving me ~0V but is not grounded. ==> I guess that getting 0.8v rather 3.3 can let me think that there's a short on the powerline. Is that a correct hypothesis? ==> How could 5V becomes 0v? ==> Is it common to have this chip defective? or is it more just a consequence of another short on the mainboard? * During my sanity checks, I tried to measure most mosfet that could be connected to the 19v powerline. One of them (which seems ok) has one pin to 25v. Is it normal? I would expect to have nothing more 19v. (maybe a newbie question ![]() * Most mosfet are 4N VUC. My research let me find that it could be PE528BA. However, I'm not able to find out what VUC stands for? Are 4N VUB and 4N VUC the same components? https://datasheetspdf.com/pdf/1094106/UNIKC/PE528BA/1 I'm looking for any guidance, any advice. I'm really doing that only for few weeks so, I'm clearly not an expert. I can provide pictures if it can help. Thanks ![]() Alex |
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#2 |
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![]() For the Fet on the +19V line it needs the gate pass to switch on more than +22 to +28V ( N-Channel Fets ) is need to gate by pass the Voltage, for the Richtek RT8249C pin 6 & 20 voltage ? what is the resistence to GND on the Colis of 3/5 ALWS voltage , find out the Bordview or close on 1
Last edited by techtiger; 03-25-2021 at 12:36 AM.. |
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#3 |
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![]() Yes, your +3V LDO is shorted somewhat. Measure resistance on PIN3 as well as Pin 13. Then remove the chip from motherboard(2N). Now measure resistance on both pins again. Compare Values. If the resistance goes significantly up, most likely the chip itself is bad. Else, you need to inject some voltage on those pins to find the shorted component. There is bright chance of EC being bad.
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#4 |
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![]() Hi techtiger and mcplslg123,
First, I want to thank both of you for your reply, it's appreciated ![]() I have attached some pictures took with my phone (sorry for the quality). @techtiger:
@mcplslg123:
Quick question: if I do voltage injection, should I put the cooler back on the cpu? just in case? |
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#5 |
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![]() Answering to myself at least on one question: EC stands for Embedded Controler.
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#6 | |
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![]() Quote:
EC embedded controller SIO (super input/output) KBC microcontroller in computers that handles various system tasks Last edited by techtiger; 03-25-2021 at 01:16 PM.. |
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#7 |
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![]() Thanks for the feedback. I knew what super io was but didn't know EC could be the same component.
So, I did some more tests and I believe I'm making progresses. The facts I have right now are:
These facts let me think that my EC can be dead (as mcplslg123 suggested). Before going further (attempting a replacement), I'm looking for a proof of that. I'm considering doing that:
Is it a good approach or not? I mean, I know it's what was suggested. What is unclear to me is whether I should do this voltage injection with or without the RT8249C on board. I've made some researches on my EC and I know for sure that changing it is not so easy for an hobbyist like me (soldering and reprogram). I want to make sure I have the right diagnostic. Last edited by alexvan59; 03-26-2021 at 07:15 AM.. |
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#8 | |
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![]() Quote:
You mentioned measuring 1ohm across 3 capacitors. This is an indication of a short. I would instead inject voltage (starting with voltages and current you mentioned) directly across the capacitor and see what gets hot. Just make sure to identify which side is positive and ground. If nothing gets hot right away, try increasing only the current first. Then increase the voltage if needed while making sure not to go above 2.5 - 3V. Examine the caps you said had low resistance physically. Usually shorted caps have slightly different color than the rest. Although I suspect since they are close to the EC, it could well be a dead EC as mcplslg123 suggested. |
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#9 |
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![]() Ok, will try that tomorrow.
Currently, on the + side of these 3 caps, I get ~0.18V and 1 ohm to GND. |
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#10 |
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![]() Adding a picture to show the shorted caps (in case somebody else get a similar issue in the future).
I have another caps behind the board that seems totally shorted (less than 1ohm on both sides of it). |
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#11 |
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![]() Hi,
Made the voltage injection this morning. Here are the results:
The chip ITE IT8995VG-128 is cheap (on AliExpress). The programmer is actually expensive (~100€ on ebay). Still worth it if it enables me to save this laptop. Since I don't know whether the other parts of the laptop are ok, I would like to delay the purchase of the programmer as much as I can. My plan would be the following:
Is it a good plan? Is it risky to replace the chip without programming it and powering the system? If yes, what can I do to delay the purchase of the programmer to maximum? Sorry for my long messages, I'm trying to give as much information as I can to enable decision making. PS: I have rework station, flux, etc. Never changed BGA on a computer mainboard on but I have changed some other chips like "tristar" on iphone. Last edited by alexvan59; 03-27-2021 at 03:43 AM.. Reason: adding small details |
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#12 | |
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![]() You can actually buy the chip pre-programmed. This seller did come recommended in a few places (https://www.ebay.com/usr/pitstopcomputers?ul_noapp=true). And they do reply to messages fairly quickly.
Try contacting them with the chip you need and your laptop model. Quote:
3,4. You could do that, just keep in mind that some of the chips labelled as "new" on aliexpress are parts that have been pulled from other devices and may already have a program in it. Not sure to what extent that could be harmful (if at all) when soldered on a different device. |
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#13 | |
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![]() Programming this chip is not easy either-so the best bet is to buy pre-programmed chip from a reliable store.
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#15 |
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![]() Ok, will prefer the option of buying preprogrammed if I can.
So, I did 1 and so, removed the chip: * the three caps around the ec are no more shorted * one cap behind still totally shorted (see picture) I removed the remaing cap to see if it could be it. However, the short remain. Since I really don't know which side is + (0 ohms and was 0v), I'm a little bit lost on how to find out what could generate this short. The bad news is that, while removing the chip, 2 pads are gone ![]() |
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#16 |
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![]() What is the reference of the IC in close to the cap? Look for its datasheet and use its pinout as reference to find which pad of the cap is ground. Looking at the picture, I would guess the top pad of the cap is ground.
For the BGA maybe you pulled it before it was fully melted, but the damage does not look bad. Its easily fixable with jumper wires. Just make sure to properly secure the wire once soldered (ideally you should use UV curable soldermask paint). Do you have schematic and/or boardview for your motherboard? Last edited by Spider1211; 03-27-2021 at 10:23 AM.. |
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#17 | |
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#18 |
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![]() Different boards have different thermal mass which affects how long it takes for the solder to melt. What I usually do (especially with bga) is to nudge the chip first, if it moves and goes back to its initial position you know all the balls have melted and is safe to remove the chip.
Mistake happens, that how we learn and improve our skills ![]() Try to look on the forum or post a request in the schematic section. Last edited by Spider1211; 03-27-2021 at 11:07 AM.. |
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#19 |
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![]() The chip close to the cap has "548 TI 711 ATCK". Didn't find the datasheet yet.
Just to be sure: you believe top pad is ground because we have a huge track or is there any other reasoning? |
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#20 | |
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![]() Quote:
![]() Thanks for all your tips, it really helps me. I don't give up until I'm sure it's total game over ![]() |
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