Acer aspire 5943g repair

[bollin]

Re: Acer aspire 5943g repair

Ok, I was doing some other stuff when I found some spare rt8206b chips. So, I replaced PU6, and I guess now B+ is about 12.5v (fluctuating between 12.2v & 12.8v), and I hear a fast ticking sound, probably from when voltage builds up in a coil. +3valw and +5valw are not working (ohms to ground PL5 5ohm, PL4 1.3 ohm) and very low voltage.
I recall lifting those coils and found the shorts to be on the rail (probably wrote about it in an earlier post). But, since the ticking sound there are still Mosfets to be checked on B+

[bollin]

Re: Acer aspire 5943g repair

I wonder if those rt8206b chips are counterfeit, since I ordered them for a another laptop project, and that didn´t get any better. Maybe I´ll order some samples from TI and get a tps51427.

[Agent24]

Re: Acer aspire 5943g repair

Ticking is most likely the controller restarting over and over due to a short - detecting the short, shutting down, waiting to see if the short has cleared, starting up again, detecting the short, shutting down.. ad infinitum...

If the controller was fake it would probably either blow up or do nothing.

[bollin]

Re: Acer aspire 5943g repair

That would make sense since both 5valw and 3valw are shorted. I guess the next thing to do is to lift the coils and try to find the shorts. But what about the B+ voltage dropping to ~12.5 volts from 19 volts that it should be? Is this because of the short aswell?

[Agent24]

Re: Acer aspire 5943g repair

But what about the B+ voltage dropping to ~12.5 volts from 19 volts that it should be? Is this because of the short aswell?

Most likely. Even with the controller(s) power cycling, there may be more load than normal which could upset the other rails.

Find the shorts, fix them, and then troubleshoot the B+ if it's still too low.

[whaldsz]

Re: Acer aspire 5943g repair

Measure the resistance of B+ to ground. if the resistance are in the range of kiloohms, then you have to check the high-side mosfets first because these mosfets are connected to B+.

Also remove the RT8206B and do a resistance and voltage test at B+ to confirm that it's not causing the fluctation.

Fluctuations in B+ rail are caused by components (capacitors, mosfets, chips) directly connected to it.

[bollin]

Re: Acer aspire 5943g repair

I desoldered jumer PJ1 and PJ4, lifted U42 & U44 and the short on 3valw and 5valw is still there. I think I am jumping to conclusions but I am starting to suspect southbridge (U60).
I haven´t got a external power source at home, but I am taking classes in electronics so there I can try to apply power to those rails to see what is getting hot. How did that thing work again? Apply 1 volt and slowly increase amperes?

[dellxps15]

Re: Acer aspire 5943g repair

according to me, ur supposing to have short both 3valways and 5volt always, but if u removed battery, removed pj1 then or short is in pc52, pc54 pc53 and still short...
i suspect u dont have short there.
remove pl1. short somewhere?


solder it back.

remove pu6 u have 19volt on pr47 ?
remove pr47 short on wich side ? B+ or dcin ?

PS: for short multimeter in diode mode. 001 002 is short.

if u sure short is on 3valeways remove jp1m pl5....still short? remove pc 52 pc 53 pc54. still short? remove pu5... still short remove pq25, pq28?still short ? ghost in the notebook....

according to lab psu, if u dont have a thermal camera, if it's a 0402 caps u risk to burn the board layer with some damage. that's my advice.

[bollin]

Re: Acer aspire 5943g repair

I might have been a bit unclear in my posting. PJ1 in place I get 1.5 ohm at PL5. Remove PJ1 and infinite ohms at PL5, 1.5 ohms at U42 pins 5-8. PJ4 in place PL4 measures 7.5 ohm. Remove PJ4 and I get infinite ohms at PL4, 7.5 ohms at U44 pins 5-8. This tells me that there are shorts on +3valw and +5valw, not +3valwp and +5valwp.
I need to check caps connected to ground on those rails.

[dellxps15]

Re: Acer aspire 5943g repair

i never measured in ohms since my multimeter is the yellow chip and ohms fluctuate very much.

it could also be pch in short. since it need both 3valw and 5valw.

if u can remove pch.

[bollin]

Re: Acer aspire 5943g repair

Well, it is very steady at those values, but I haven´t subtracted the resistance in the probes, so in reality it is probably about 0.5 ohm lower.

That´s sort of what I was thinking too (PCH). Unfortunately, I haven´t successfully removed any bga chip so far... However I will give it a go, but only when I have exhausted other possibilities.

[Agent24]

Re: Acer aspire 5943g repair

It may not be your chipset that is shorted, or even anything shorted:

https://www.badcaps.net/forum/showthread.php?t=35519 (Post #19)

"Forget the continuity test when looking for shorts on laptop mainboard. 15 ohms is normal resistance for low voltage rail which supplies northbridge, 6 ohms is normal resistance for graphics chip."

[bollin]

Re: Acer aspire 5943g repair

Found the short on +5valw! U56 was shorted between pins 1, 2 & 3. I lifted the whole side and now it is gone. Did check the legs on u56 when lifted and it confirmed it. Next is to hunt down the short on +3valw...

[Agent24]

Re: Acer aspire 5943g repair

Sounds good... what kind of device is U56?

[bollin]

Re: Acer aspire 5943g repair

U56 is a rt9715bgs, "The RT9715 is a cost-effective, low-voltage, single
N-MOSFET high-side Power Switch IC for USB application".

[bollin]

Re: Acer aspire 5943g repair

As I tested U41 (bios, mx25l1005a) ground pin broke off. I ordered new parts, but I can´t understand the programming. Isn´t it 1mb flash only? the bios .bin file is 4 mb, and SPI is .rom and 128kb. SPI is U32 (mx25l3205d). shouldn´t these be the other way round (4mb goes on 32mb flash, 128 kb goes on 1mb flash)?

[dellxps15]

Re: Acer aspire 5943g repair

megabit not megabyte.

32mbit = 32/8 = 4megabyte.

[bollin]

Re: Acer aspire 5943g repair

Ok, that makes more sense. I will need to flash them both so they have the same version, right?

[dellxps15]

Re: Acer aspire 5943g repair

no need for that.

[bollin]

Re: Acer aspire 5943g repair

Ok, thank you for your help. I will report back with findings, however atm it seems it is either u34 or pch that is faulty.