Wednesday, 22 September 2010

When Memory Goes Bad

My test box has a Pentium-4 motherboard with 1Gb of memory in 133MHz PC2100 DIMMS. I know: antique. In dog years this main-board is about 70 years old. In tech years that's about 140. Only slightly younger than me.

It worked perfectly for the g/f to check her email. Later I come back to install Maverick from the CD. I start it up and... the machine hangs at X, before the GDM login. I think I have a hardware bug which is stopping the Maverick boot or more likely the X-server.

Now I'm in fault-finding mode...

I mess around with CD boot options - remember pressing the Esc key shows you the boot messages and F4 brings up the boot options menu.

Nothing. Nice wallpaper. No GDM login.

I remove the CD and boot as normal.

Nothing. Nada. Black screen.

Something's gone seriously wrong in the hardware.

This maching has no case. It sits in a perspex box with the backplate on the front and the power supply hanging out the back, the hard drive and optical drive rest on top. It's very 1979 Blake's Seven.

Unplugged the hard drive, still nothing. Not that. Unscrewed the lid, removed both DIMMs. Now I get the POST beep for no memory installed. OK. Put a DIMM into slot 1. Nada. Black screen. No beeps.

Switch the DIMM for the other one. Nada. Black screen. No beeps.

I fish out some old PC2100 DIMMs and put one of those in. Nada. Black screen. No beeps. Two dead DIMM's could be coincidence. Four is beyond possible.

So I put the original DIMM in slot 2.

Ta-da! Working machine! So I put the remaining original DIMM in slot 3.

We're back with 1Gb memory.

So I have one dead memory slot on the motherboard. Maybe it's heat expansion in the plastic over the years, or a gold contact has delaminated or bent.

A bit of considered fault-finding tracks down the problem without diving into too many rat-holes. It's the first time I've had this fault. Had I not been building these things for years I could have lost days tracking that down. You've got to break down the problem into symptoms and causes. Not obvious with this one. Logical? Barely. Smug? Slightly. RC

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