The Natural Philosopher wrote:

Also check if your BIOS has a fast A20 gate option. If it does, and
its turned off, then turn it on and try again! (Why is a long and
complex story!)


mmm.


Have you also tried a differnet keyboard?



nope. I don;t think that is th eproblem tho...

Unlikely granted - but due to a strange IBM design decision many years
ago - potentially related! (A gate introduced into the A20 address line
of the first 286 based PC (the AT - to allow more accurate emulation of
the original 8088 memory architecture) was implemented in the keyboard
controller - since they was the main bit of original design they did -
the rest was lifted from Intel / Shugart data sheets. They also lumped a
few other bits of unrelated functionality in there - like the ability to
reset the processor! Hence on the first PC-AT computers things like
getting the 286 to switch from protected mode back to real mode (which
required a controlled reset) involved sending a message to the keyboard
controller over a serial link!

I roasted it good and proper - that fan has been stick all summer I reckon.

Heatsink was about 70C with the fan off.

70 does not actually sound that bad.... might have done some damage -
but not a dead cert.

The fact that its oinconsistent and seems temperature dependent leads me
to a hardware explantion.

I would tend to agree. There has also been a spate of motherboard
problems recently due to poor quality capacitors that were supplied to a
number of the big OEMs and motherboard makers. Many of these are
starting to show up as failures now they are a couple of years old. This
would also hold with your suspicion of a timing related problem.

Is the keyboard UART integrated on the pentium? Or is it a separate chip?.

It is integrated into the "chip set" on the motherboard - rather than
the processor itself.

I can change motherboard, processor or m,emory, but don';t want to
change all three - expensiove

How many DIMMs do you have fitted?

If more then one, you could try running with only one device fitted for
a bit - then swap to the other and see if that has any impact. If it's a
memory problem then its unlikely to be a fault in both devices.

If only 1 DIMM, then buy another one the same and try that (RAM is cheap
enough at the moment!). Even if it does not fix the problem you at least
have an upgrade for your money!

Next thing to replace would be the motherboard.

the master PIC so it usually has priority over most interrupts except
the system timer (assuming the 82c59 equivilent in the chipset is
still set to "special fully nested" mode, as it is in the BIOS
initialisation!



Its windows 98 so its fairly primitive.

You will find the interrupt handling on W98 is actually pretty
sophisticated! It uses several layers of drivers split into different
processor operating modes. This is mostly to allow virtualisation of the
DOS environment. A DOS application can run, and bang away at the
interrupt hardware as much as it wants, in the full belief that it is
twiddling bits on the actually interrupt controller. Meanwhile there are
several other applications all doing the same in parallel! This is all
handled by a virtualisation of the interrupt controller implemented in a
VXD.

probably a rash assumption these days since the whole lot is
virtualised by protected mode code in the VXDs that deal with mouse
and keyboard anyway)



In W98?

Very much so. In some respects W98 has to pull some quite "clever"
tricks to achieve what it does - not because of its stunning design -
more a case of given the choice you would not have started from DOS!

Socket 370 I hope ;-)



Dunno. Lost of pins and a square socket.

That is socket 370 then - motherboards are getting thin on the ground
but some should still available in this form. (the first PIIIs were
"Slot 1" devices - getting a MB for one of these would be a non starter).

What case style have you got AT or ATX (the latter are easy to recognise
because they have a rectangular section at the back where all the
motherboard mounted IO connectors meet the outside world).

Again if you have an AT style case then getting a motherboard will be a
non starter.

Most new motherboards will be either Socket A (AMD) or Socket 478 (Intel)

If it's any use by way of illustration - I just upgraded a customers
computer with a new fully integrated motherboard and a new Duron 1.3GHz
processor - reused the existing RAM. Total cost was about 80 all in for
the hardware.


--
Cheers,

John.

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