PB (Acer) LA-5891p mainboard not starting

[Thakkie]

I have a Packard Bell (Acer) NEW70 LA-5891p mainboard that is not powering up.

I have checked the CMOS battery and it was completely empty. I have removed the battery and found that the charge voltage is only 1 volt.

The +RTCVREF, directly from the regulator (PU14 pin 3), is 3.3V.
The resistance from +RTCVCC (D8 pin 3) to ground is about 180 ohms, obviously not OK.
When cutting the +RTCVCC at D8 pin 3, the charge voltage on the battery returns to normal.

I have checked the board for visible defects or burn marks, but found nothing.

My hypothesis is that there is either a bad cap or that the chipset is fried.

I'm having trouble locating the related caps as they are not market with a sikscreen.
At the moment I do not have access to tools to reball the chip, so I'm hoping it's a bad cap or a short of some kind.

I attached the schematics document so you can look up the test points I've mentioned.

Could anybody please advise on how to go from here?

Thanks in advance

Jan

[bicalov]

Re: PB (Acer) LA-5891p mainboard not starting

Maybe this can help. the LA-5892 is also Aspire 5741

[dj_ricoh]

Re: PB (Acer) LA-5891p mainboard not starting

Yes!
The board view will come in handy.

The first thing you search is the always V

3.3v and 5v on the output you will always find coils on those outputs.

Its like this you lift the coils up and see what side its shorted.

We go after you check the coils

[Thakkie]

Re: PB (Acer) LA-5891p mainboard not starting

@bicalov

Thanks for boardview. The LA-5892 board is quite different from the LA-5891p and unfotunately this bvd is not very useful to me. I'm trying to get a hold of the correct bvd file, but no luck yet.

[Thakkie]

Re: PB (Acer) LA-5891p mainboard not starting

@dj_ricoh

Thank you for your reply.

I am not sure you understood my original post correctly. I don't seem to have power supply problems. +3.3VALW and +5VALW are OK as are the supply power for the RTC charge circuit and RTCREF (The output of the regulator for the charge circuit).

I'm having issues with the RTC battery (the small lithium cell) voltage.

The problem is that the RTC voltage is being pulled down by a short of some kind. I suspect there is a problem with the chipset (the large BD82HM55), but am hoping there could be a different problem I might have overlooked.

By the way Voltage on both sides of PL27 is 5.1V and both sides of PL28 3.3V no need to lift them

[bicalov]

Re: PB (Acer) LA-5891p mainboard not starting

I know there are principles, but $ 3,32 is not the world.

http:/**************************.html?___SID=U

[Thakkie]

Re: PB (Acer) LA-5891p mainboard not starting

Ah, think I missed that one. Thought I only got Russian and Chinese sites.

$ 3.32 is no problem at all!

thanks.

[atsio]

Re: PB (Acer) LA-5891p mainboard not starting

If you buy it, please share it.

[Thakkie]

Re: PB (Acer) LA-5891p mainboard not starting

Here you go!

[bicalov]

Re: PB (Acer) LA-5891p mainboard not starting

Thanks for sharing

[atsio]

Re: PB (Acer) LA-5891p mainboard not starting

Thanks

[qonma]

Re: PB (Acer) LA-5891p mainboard not starting

i have same problem....alw 3 and 5volt ready, swon 3volt, rtc 3volt, flash bios still, am reflow the chips hm55, problem solved

[day_see]

Re: PB (Acer) LA-5891p mainboard not starting

Thanks

[zpi]

Re: PB (Acer) LA-5891p mainboard not starting

Didn't you tried to inject few Volts to +RTCVCC ? See how many amps is used injecting 1V, if it will use something, you should be able to see hotspot with thermal cam, if you don't have it, try ouch method with your finger Off course it should be at least few wats of current to feel it.