Re: [Sheflug] PC Problem

[John Southern <john [at] xxxxxxxxxxxxxxxxxx>]

On Saturday 06 August 2005 19:12, bones wrote:
> A friend has recently given me a PC.  At first the computer would just say
> reset, and now it seems completely dead.......it won't turn on.  Could the
> power supply unit have packed in? Or can I reset the motherboard or
> something?  There is no noise or whirring or nothing.

"The computer would just say reset" In what way, where, how? Was this via BIOS 
beeps, or did you see something on the screen?

OK let's start with a few checks. The following is what I ould attempt.
Anyone any better ways of doing it?


If you unplug the hard drives, CD/DVD Roms, floppy drives all external bits, 
such as speakers, scanner, printers etc.,
At this point you should have plugged in the PSU, motherboard plus the 
connections to the case switches.
Does the CPU fan spin?

No? OK take out all the unnecessary cards, such as SCSI, Sound, network etc 
leaving just the video card.
Any luck now?
No? OK find the CMOS jumper and connect it as reset. turn on the machine (It 
should not do anything except load the BIOS defaults.
Change back the CMOS jumper.
Try again?
No?
OK Try reseating the RAM
No?
OK Try reseating the CPU (Don't forget to add more thermal paste to the 
CPU/Heatsink junction)
No? Borrow a PSU to test
No? Borrow new RAM to test
No? Borrow a new CPU?
No It dead.

PSUs do burn out, although rare and it is just normally the thermal fuse that 
need replacing (usually with the aid of a soldering iron).
I am starting to make sure I get plenty of extra power with PSUs and making 
400W the base for any machine I built. The more drives or higher CPU, the 
more power and also the more noise :-(

What are the machine specs?
Does it have an ATX power supply? This is where the connection to the 
motherboard is a double row of connections on a single socket. These are 
designed for ATX or NLX form factor motherboards and are the commonest you 
are likely to see.
http://www.fastlanehw.com/reviews/104/7.jpg

Check to see if pin 18 is solid and no connection. In that case it is a SFX 
board that will usually have an additional 3x2 connector that has a single 
wire connected for Fan on. These are typical in low load units and a few in 
car motherboards.

Older AT power supplies have two single row connections P4 and P5, although 
now these can also be called P9 if joined together or P8 and P9
http://www.computerwriter.com/images/smoketest.JPG
Originally these were for AT, Baby AT, PC/XT and LPX motherboard form factors.
If you have one of these and the connector is in two parts, you can easily get 
them the wrong way around. Simply put the colours together (All the black 
wires end up in the middle).

Some motherboards now use one of these connectors as an AUX connector, but it 
is wire differently from the P8/P9 sort. It is wired Gnd, Gnd, Gnd, 3.3, 3.3, 
5V. Sometimes (Tyan motherboards) these are in a 3x2 format and are mainly 
used for Fans.

The more modern P4 connector for the Intel P4 CPU is a four way connector
http://www.crazypc.com/images/cables/connectors/uvr12vfull.jpg

The most modern one I have used have 24 way ATX connections which are normally 
labelled as such and used for Intel spec'ed motherboards.
Be careful here. Some Compaqs have 24 way, but are not the usual layout. If 
you are replacing, make sure the wires are the same colour/connection.

WTX boards have both a 24 and a 22 connector, with the 24 being used for just 
power and all the control lines. These power supplies are monsters in both 
power and noise. They normally have twin fans blowing out the back and I 
recently used one that had twin fans for rear exhaust and twin fans for 
blowhole exhaust. Designed for workstations, but to be honest I hardly ever 
see them nowadays.

I am sure there are other odd PSUs out there. Anyone seen anything else?

John



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