The most likely reason is that MBM5 is not compatible with your particular motherboard.
Could a sensor be faulty...yes, that's possible too.
Could it be because the motherboard is sitting in a Compaq machine...yes.
It's just likely that your motherboard is too old to be monitored by MBM5 with acurate results. The same applies to about any other temp monitoring problem you try to use.
"However, at idle, my CPU tends to run in the mid-30s and my board (or case) tends to run in the high 20s."
Where do you get this info? BIOS? A program that came with the motherboard? Where?
That sounds like pretty good information and I'd be inclined to believe it first.
I've run a Cyrix processor in the past and know they can run hot but, no run hot by today's standards. I'd suspect a Cyrix with an operating heatsink fan would actually run in the mid 30°C range.
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