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Freezing BIOS even - any ideas why?

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4wd:
From (jaded and mutilated) memory they are expensive to produce, really expensive to buy and not fit for very high frequencies. Then again, a PSU is not high frequency.-Shades (November 24, 2010, 04:46 PM)
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All modern Switchmode PSUs are high frequency, starting from about 20kHz and going much higher.  This problem never, (well very, very rarely), appeared in older PSUs that only ran at mains frequency, (50/60 Hz).

Tantalums are unsuitable for this application because their ESR is much higher than electrolytics at these frequencies.

I do have a PSU tester so I could give that a whirl.
-Carol Haynes (November 24, 2010, 04:38 PM)
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Unless it can provide an equivalent load at switch on to replicate inrush current, it might not do much except show if the output voltages are within limits.

Wow, don't think I've ever seen that before, even with pretty fubar boxes O_o
-f0dder (November 24, 2010, 04:49 PM)
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You need to walk the Dark Side of electronics ;)

40hz:
Another possibility might be a bad trace, cold spot, or hairline fracture on the mobo. This is the other thing (along with iffy capacitors and PSUs) that can introduce weird thermal related system hangs. There's a very scary "flex test" you can do on a live system to check for board trace fractures. But I wouldn't recommend it unless you're already on the brink of packing something off to the community tip and don't care any more.  ;)

Also a damaged slot (cold spot or damaged trace on RAM slots - or whatever is hosting the video card) are other likely culprits. If a defective signal path introduces enough chatter, timeouts or corrupt data, the CPU can go into la-lah land. Swap outs will help check for that.

Got a client with a computer that freezes - even to the point of not allowing a forced switch off by holding the power button.-Carol Haynes (November 24, 2010, 02:03 PM)
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Wow, don't think I've ever seen that before, even with pretty fubar boxes O_o
-f0dder (November 24, 2010, 04:49 PM)
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Got an old HP Kayak workstation sitting in storage that does that. Sorta like a turtle - once it locks up, it stays locked up. Even after a replacement PSU and front panel switch. Only way to reboot it is to pull the AC cord.  ;D

Carol Haynes:
I am coming to the conclusion that they would be better off replacing the system. It's five years old so there is little point in wasting time and money keeping it alive - especially as it is so cranky and unpredictable.

Thanks for all the feedback - it is useful to have people to bounce ideas off when you work alone!

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