Acer Aspire 3500 Mobo weird short/CPU issue - Page 1
Forum section: electronics / beginners

author: VanMarco
author_rank: Contributor
timestamp: January 25, 2014, 09:48:05 pm
content: hi there ! SO glad to be registered on this nice forum!! I hope I got the category right!So I have this mono I've pulled from the laptop ASpire 3500 that is dead. I've tracked down the voltage from the PSU jack til the battery terminals and voltages seems to be right. then I've kept testing for shorts all around the board (MOSFETs, regulators, diodes) and I found two MOSFET near the cpu socket who were giving short so I removed them and they tested good. the pads where they were soldered still, giving short. also other components such as diodes on the other side of the board given short. then I tried to remove the CPU and without the CPU all the shorted pads and components which tested shorted in circuit tested OK. changed CPU same result. CPU in, shorts. CPU out, OK. the mobo did not start without CPU anyway.I will PosT some picture later on, my question now is quite simple, I do not define myself as a total newbie, from what I know there shouldn't be a short like this. is that normal that stuff go "short" when the CPU is in the socket? I have tested another mono and it wasn't like this.my supposition about what is faulty is that there is something wrong with the north bridge. it seems it has some heat mark beneath the heatsink.thanks for any of your replies!!

author: Simon
author_rank: Unknown
timestamp: January 25, 2014, 09:50:44 pm
content: Define "a short" don't forget that the cpu uses an awful lot of power so what looks like a short could be it's DC resistance.Really motherboards are not the best things to try and fit.

author: VanMarco
author_rank: Contributor
timestamp: January 25, 2014, 10:30:40 pm
content: Hi there, by short I mean short on the diode tester, with the board disconnected from the DC PSU

author: fluxcapacitor
author_rank: Frequent Contributor
timestamp: January 25, 2014, 10:47:30 pm
content: here is the schematic if you havnt already got it .http://kythuatphancung.com/download/acer-aspire-3000-3500-5000-compal-la2362-laptop-schematics.html

author: VanMarco
author_rank: Contributor
timestamp: January 25, 2014, 10:53:11 pm
content: thank you mate!!

author: Simon
author_rank: Unknown
timestamp: January 26, 2014, 07:54:20 am
content: that is not a short, the processor uses anything down from 1.5V (probably more like 1.25) to 0.8V, of course your diode tester rsisters current going into it, processors use 10's of amps, the equivalent resistance is very low.

author: amyk
author_rank: Super Contributor
timestamp: January 26, 2014, 09:34:22 am
content: Over 100A peak at ~1.2V for some of the highest-end CPUs, but that's dynamic power draw; static is still in the tens of amps, so the DC resistance across the Vcore is <1 ohm.Also you should remove the CPU from the socket if you're going to do any probing with an ohmmeter, as they're very low-voltage devices and can be easily damaged with just a few volts. Even tens of mV difference in core voltage is already a huge amount for a device designed for 1.4Vabsolute max.

author: VanMarco
author_rank: Contributor
timestamp: January 26, 2014, 11:41:19 pm
content: Thank you for all your replies!! Yes, I did know about the CPU sensitivity to "esd" or voltage thru the multimeter, but I didn't bother much, Intel 2004 lol. I have many CPU same as that oneI will start to check everything again with no CPU in it and sorry I didn't post pictures I had too much to do!Thanks again!