On 19 Jul 98 at 22:08, Joel Bluming wrote:

> I left a 486x100 on over the weekend to test my remote dialup setup. It
> worked fine one day, and not the next. When I arrived home I found
> (obviously) that the machine was frozen.
> When I tried to reboot nothing. No post. I swapped in a known good CPU of
> the same type (Intel DX4 100) - no go.
> The drive is spinning, The fans are working.
> Where should I begin? Motherboard, power supply, what?

  DX4 CPUs need a regulator to step the supply voltage down from 5v
to 3.3v. There are two common sorts -- switching and linear.
  A linear regulator is cheaper, but it blows off the excess energy
as heat.  Leaving it running like this could allow the regulator to
overheat; typically, a few of its components have heat sinks, but
these become less effective as the temperature in the case increases.
  [I assume most of you know what outside temperatures have been like
this past week....]

  I had one of the SCRs in a linear voltage regulator overheat and
explode a while back.  You have to know where to look to spot the
cratered component, but the other symptoms are much as you describe
-- power to drives and such, but none to the CPU and so no POST or
other signs of life.

David G