Acer Aspire 5750-6845 dead

[tibimakai]

Re: Acer Aspire 5750-6845 dead

The 4.286V is on the base(single pin) of the transistor.
I will check those voltages on the U20.
Where would I find this IC if I have to buy it? Ebay?

[whaldsz]

Re: Acer Aspire 5750-6845 dead

The 4.286V is on the base(single pin) of the transistor.
I will check those voltages on the U20.
Where would I find this IC if I have to buy it? Ebay?

This reading looks normal.

[tibimakai]

Re: Acer Aspire 5750-6845 dead

At U20 is all the same, basically is 0V on all those pins.
So, I guess I need to change this IC?

[lorins_core]

Re: Acer Aspire 5750-6845 dead

About The U20. Can You Check if they Have Open Connection in PIN? or Try To Resolder...

[tibimakai]

Re: Acer Aspire 5750-6845 dead

Could you please be more specific? I don't really follow you.

[lorins_core]

Re: Acer Aspire 5750-6845 dead

Ok... sorry. About The U20. They have A Pins. Take A Look Proper. If you Have A Electronic Microscope Better can Check The Pins To Connection Edge on board. Maybe They Have Corroded Or Cold Solder. You need to Resolder. or if You Have A HotAir Reworks Station Remove the IC and Clean The Terminals and Re install The IC (U20)
...

[tibimakai]

Re: Acer Aspire 5750-6845 dead

OK, thank you I understand now.
I have USB microscope and hot air station too. I will give it a try. It looks scary though. It will be my first time soldering something with so small pitch.
I may try just reheating it first.
This would be the IC?
http://cgi.ebay.com/ws/eBayISAPI.dll...:X:AAQ:US:1123

[whaldsz]

Re: Acer Aspire 5750-6845 dead

The 4.286V is on the base(single pin) of the transistor.
I will check those voltages on the U20.
Where would I find this IC if I have to buy it? Ebay?

U20 or PU2?? Of course you still dont have the 3.3v and 5v you wont get any voltages at U20.

[tibimakai]

Re: Acer Aspire 5750-6845 dead

Measure the voltage at pin 2 of PQ25, EC_ON pin 2 of PQ27.

I was re reading these posts and I don't remember measuring PQ27. I had measured PQ24 and PQ26. It matters at this point?


U20. I don't know what is PU2? You said to recheck the voltages on U20.

[whaldsz]

Re: Acer Aspire 5750-6845 dead

Looks like your voltage readings on PQ24 is ok. Why? there is a voltage at the SOURCE of both mosfet(see ) that is enough to put ENTRIPx high and make VOUTx to give 3.3V, 5V at PL4, PL5, provided pin13 EN Of PU2 is also high.

On PQ26, the result is odd. 4.286V is for pin 1 right?

One more time, could you please measure all voltage at the pins of PU2 for confirmation before you change this IC?

I am referring to the above post. Measuring pin32 of U20 (see post #25) no longer matters because surely, you don't have any voltages there. U20 gets its supply from +3VALWP on PL4 found in the circuit of PU2.

Could you measure. The voltages at all pins of PU2?

Also measure the resistance with respect to ground of PL4 and PL5.

[tibimakai]

Re: Acer Aspire 5750-6845 dead

OK here are the voltages:
Pin #
1= 1.53V
2= 0.065V
3= 1.998V
4= 1.998V
5= 0V
6= 1.114V
7= 0V
8= 3.27V
9= 4.5V
10,11,12= 0V
13= 3.17V
14= 1.998V
15= 0V
16= 19.22V
17= 4.96V
18= 0.065V
19= 4.96V
20,21= 0V
22= 4.472V
23= 0.001V
24= 0V

[whaldsz]

Re: Acer Aspire 5750-6845 dead

Since pin 19 is HIGH, clearly it's in OverVoltage Protection (see datasheet of RT8205 on page 23 under the section OUTPUT OVERVOLTAGE PROTECTION (OVP) ).

1. Check PQ21 if defective.
2. Check resistance across PL5 and ground.

[tibimakai]

Re: Acer Aspire 5750-6845 dead

PQ21, PQ20 and PQ34 are shorted between pins 1,2,3 and 4.
PQ33 it's OK.
Between PL5 and ground there is only 100 Ohm.
Between PL4 and ground, there is only 0.6 Ohm.
Doesn't look good.

[whaldsz]

Re: Acer Aspire 5750-6845 dead

So the overvoltage is caused by a short in PL4.

When you tested PQ21, PQ20, and PQ34, did you test between Source [123], Gate 4, and Drain [5678] - pins 1 2 3 and pins 5 6 7 8 are connected together?

Anyway, remove PL4, check resistance between the two pads to ground - this is to locate if the short is in the load side (+3VALWP) or the MOSFET side (PQ22, PU2).

[tibimakai]

Re: Acer Aspire 5750-6845 dead

Pins 123 and 5678 are connected together. Between 5678 and 4 there is no short. Short is only between 123 and 4 on all three transistors.
Later I will remove PL4 and I will test it.

[tibimakai]

Re: Acer Aspire 5750-6845 dead

OK, the short is not toward the FETs. At PC42 side is the short. At the +3V ALWP.

[whaldsz]

Re: Acer Aspire 5750-6845 dead

See page 56 of the schematic diagram, it will help you isolate the short.

[tibimakai]

Re: Acer Aspire 5750-6845 dead

Unfortunately, I'm lost in this schematics.
I don't understand from where is coming that 3V?

[whaldsz]

Re: Acer Aspire 5750-6845 dead

+3VALW comes from +3VALWP on page 46 through jumper PJ7.

On page 56, you see that +3VALW supplies many sub-circuits - +3VALW_PCH, +3V_LAN, +3VALW_EC, +3VS and +3V. You just need to isolate those circuits and test the resistance to ground, just like what you did to PL4.

Simpler way is to use a variable DC Power supply to identify the shorted component. Set the voltage to 0.3v and solder the +wire to +3VALW and -wire to GND. Start with 0.3V and gradually increase the voltage until you notice the heating shorted component. Be careful not to set the voltage too high or you end up damaging other components. There are tutorials on youtube for additional reference on this topic.

[tibimakai]

Re: Acer Aspire 5750-6845 dead

I didn't get to far, didn't have much time, but looking at the block diagram and trying to find those components, I hit a road block.
Pages noted in there, do not match the service manual(a,b) and for example on my board is missing U14. U21 has only one Q25, not two as in the service manual.
U21 has all the 5,6,7,8 pins together shorted to the ground(0.6). The other pins are fine.