Acer aspire 5943g repair

[bollin]

I have got a acer aspire 5943g that I am attempting to rescue for a friend.
I have taken it apart, and here´s what I´ve found:

1. PL1 (smb3025500ya_2p) is toast! A coil right after the DC jack.
Since I don´t have any spare boards right now, I don´t know where to find a replacement... Any suggestions on what value to put there or where to source a replacement?

2. There seems to be several shorts to ground on the coils (PL4, PL5 & PL11), at least on +3VALW and +5VALW. Some Fets are bad and needs replacing so i´ll just go ahead and order some.

Until they arrive, I think i will desolder some parts to see if its only the fets that are bad or if perhaps pu6 is bad too.

Here´s the schematic.

[Francisco.s]

Re: Acer aspire 5943g repair

I have got a acer aspire 5943g that I am attempting to rescue for a friend.
I have taken it apart, and here´s what I´ve found:

1. PL1 (smb3025500ya_2p) is toast! A coil right after the DC jack.
Since I don´t have any spare boards right now, I don´t know where to find a replacement... Any suggestions on what value to put there or where to source a replacement?

2. There seems to be several shorts to ground on the coils (PL4, PL5 & PL11), at least on +3VALW and +5VALW. Some Fets are bad and needs replacing so i´ll just go ahead and order some.

Until they arrive, I think i will desolder some parts to see if its only the fets that are bad or if perhaps pu6 is bad too.

Here´s the schematic.

Thanks for the shematic and dont be worried about PL1, It is there only for RF interferences. (EMI)
If it is toast, is because too much current has passed through it, probably due to a short-circuit in any capacitor or mosfet.
You should disconnect all circuits it is connected to, one at a time to find out which is the culprit.
Check in ohms pl1 against gnd. (it is better checking ohms that voltage or current)
Good luck.

[bollin]

Re: Acer aspire 5943g repair

Thanks, so If i can´t find a replacement I can just make a solder bridge, right?
I checked PL1 to GND, that is about 65kohms so thats allright. Still got the +3v and +5v and GPU power rails to fix, only waiting for parts.

[Francisco.s]

Re: Acer aspire 5943g repair

Thanks, so If i can´t find a replacement I can just make a solder bridge, right?
I checked PL1 to GND, that is about 65kohms so thats allright. Still got the +3v and +5v and GPU power rails to fix, only waiting for parts.

Yes, but there is not a short-circuit?

[bollin]

Re: Acer aspire 5943g repair

No, it had just broken off one solder pad and was damaged physically only. +VIN is not shorted.

[bollin]

Re: Acer aspire 5943g repair

It is time to start up this project again after a long time. Earlier I have desoldered the coils and found that the short is after the coils. I also did some voltage readings and found that on pl4 there is 0.04 volts but pl5 shows 0 volts. PQ34 shows a short between gate and ground, so could PU11 be faulty? What´s the easiest way to find the problem on the +3valw rail?
btw I measured b+ to 3.4 volts on pu6, which is way too low...

[bollin]

Re: Acer aspire 5943g repair

It is time to get this project finished now. Can anyone tell me what to check? B+ after pq10 reads 3.4 volts and I don´t really know where to start looking. Is it PU5? circuit protection?

[whaldsz]

Re: Acer aspire 5943g repair

If B+ reads 3.4v then it indicates a short in B+ rail.

1. Try to measure the resistance of B+ to ground.
2. Check PQ10 if ok.
3. Measure the voltage of PQ10 at pin 4. For normal operation, it should read around 11v.
4. Measure pin7 of PU4B. This pin shold be HIGH (voltage to equal to VL).

[bollin]

Re: Acer aspire 5943g repair

1. Resistance to ground is infinite (no sign of short)
2. Pq10 has been desoldered, tested good and resoldered.
3. Pin4 voltage is 18.85 volts, same voltage on pins 1-3
4. Voltage on pin7 is 0.02 volts

[whaldsz]

Re: Acer aspire 5943g repair

1. Resistance to ground is infinite (no sign of short)
2. Pq10 has been desoldered, tested good and resoldered.
3. Pin4 voltage is 18.85 volts, same voltage on pins 1-3
4. Voltage on pin7 is 0.02 volts

There you are - .02v at pin7 of PU4B would short PD5 to ground and would force PQ21 to turn off. A voltage coming from PACIN is also needed because it supplies the voltage needed at the gate of PQ21.

PACIN comes from PU1A. Again, to have an output, pin3 voltage should be higher than pin2 voltage.

Finally, check the voltage and resistance to ground of pins 5,6,7,8 of PU4B. For normal operation, the voltage at pin 5 should be higher than the voltage at pin 6 to be able to get a correct voltage at pin 7.

[bollin]

Re: Acer aspire 5943g repair

PU1A:
pin1: 17.12v
pin2: 3.21v
pin3: 3.54v

pq21:
s: 0v
g: 0v
d: 16.35v

PU4b:
pin5: 0.65v, infinite ohms
pin6: 3.14v, infinite ohms
pin7: 0.02v, about 140k
pin8: 18.5v, infinite ohms

These are all readings with components still in circuit, I haven´t resoldered anything.

[whaldsz]

Re: Acer aspire 5943g repair

PU1A is ok.

PQ21 reading is not normal. D should be 0v. Why? Gate should be 3.3v, shorting DRAIN to ground. This 3.3v comes from PACIN at PU1A.

PU4B is not ok. Pin 5 should have voltage higher than pin 3. Check PR37 and PR42 if resistance is 499k ohms. Also check the voltage of B+.

[bollin]

Re: Acer aspire 5943g repair

B+ voltage is 3.44v
I need to desolder the resistors, as the values are rising/declining depending on polarity of my probes... i'll report back in a moment

[whaldsz]

Re: Acer aspire 5943g repair

B+ voltage is 3.44v
I need to desolder the resistors, as the values are rising/declining depending on polarity of my probes... i'll report back in a moment

3.44V at B+ indicates a short in 19v rails. You can do the following the further isolate the problem:

1. With the adapter plugged in (but not power button pressed), measure the voltage at all coils, see if you can get any voltage readings. Any voltage reading will point to a faulty HIGH SIDE MOSFET.

2. Lift coils and measure B+ to isolate the fault such as

• +INVTRPWR_B+ - L2, L1
• CHG_B+ - PL25, PL22
• RT8205_B+ - PL3
• etc.

3. If you were able to isolate the problem to a particular section, check the capacitor that is connected to _B+ in that area.

[bollin]

Re: Acer aspire 5943g repair

Ok, I measured voltage on coils, all i could find was 0.04v on pl4 and 3.4v on pl13.
I´ve managed to catch a cold now, so maybe i´ll feel better tomorrow and try to isolate the problem even more.

[whaldsz]

Re: Acer aspire 5943g repair

Ok, I measured voltage on coils, all i could find was 0.04v on pl4 and 3.4v on pl13.
I´ve managed to catch a cold now, so maybe i´ll feel better tomorrow and try to isolate the problem even more.

It won't make sense to measure PL4 because there is a short in 19v supply (B+) rail. To be able to isolate which section of your motherboard is causing this short, you have to temporarily disconnect the coils that provides 19v supply. Please see my previous post.

To disconnect RT8205_B+ from main B+, remove PL25 and PL22, then test the voltage or resistance at B+. Do this repeatedly for other circuits that connects to B+.

[bollin]

Re: Acer aspire 5943g repair

Yes, I know what you meant. It was to test the high side mosfets, but according to that they seem to be ok.
I can't locate pl22 & pl25, neither in the schematic or on the board itself. But i get the idea and I think I will desolder resistors where i can' find coils.

[bollin]

Re: Acer aspire 5943g repair

Ok, the problem with b+ is in the ISL6237_B+ circuit. I cleared PJ19 and B+ was 19.2v in the rest of the circuit. So, now I´m going to test caps in the ISL6237_B+ circuit until B+ voltage is 19.2v there aswell.

[bollin]

Re: Acer aspire 5943g repair

Ok, removed, tested and replaced pc44, pc45, pc46, pc47 and pr81. B+ voltage was at 19.2v when pr81 was removed. I then removed pc48 (and broke it in the process), b+ was at 3.44. That leads me to the conclusion that pu6 (RT8206bgqw) is the culprit. I will order some parts now, and hopefully I´ll get them very soon.

[whaldsz]

Re: Acer aspire 5943g repair

great!