22 Jan
2008
22 Jan
'08
2:11 a.m.
Richard A. Cini wrote:
Status of the RESET line and power_good signal? I
don't know if the original
power supplies had a "power good" signal but I know that on newer machines,
if the power is out of tolerance, it won't POST.
<snip>
>
> I DO have a good meter, and a scope (and I know how to use it!)
>
>
Look and see if the processor is being held reset, or if there is
activity on the memory bus control lines. I don't have an 8088 pinout
handy, but there are bus state lines that should be pretty quiet if you
hold the processor reset. If they are rattleing then you got a lost
processor somewhere if the bios isn't posting.
Best would be a post card to decode outputs to port 80, but ... not on
your list.
The state lines are decoded by various parts of the hardware to
determine if the bus is doing memory operations, I/O or other
activities, so if they are going on a scope you can't infer much other
than enough circuitry is going to make the processor run around.
If the processor is not held reset, then there is not much to do but
probably try to find a post card. There isn't much what you have will
tell you as lots of things get signals, and you can't sync on much to
tell what is working and what isn't.
On the motherboard, the reset should be a short lived event. If it is
held down, you probably have a bad power supply. There is no reset
switch on an IBM PC, and other than the one applied by the power supply
at power good, and when you do control alt delete, you won't be seeing it.
Hope this gives some ideas.
Best things to find somewhere is the advanced diagnostics set, which has
lots of what you need, and a Post card, assuming the above don't suggest
something.
Jim