Hello all,
I have an IBM PC, 5150, 16-64KB motherboard, that appears to be dead. Power
on produces no display or disk activity (even after a while), and no beeps
from the speaker (I tried a couple of speakers, so I don't think it is a
speaker issue.
From what docs I found on the internet, the
switches are set up properly for
the machine's configuration...
I am pretty sure the motherboard is getting power. I checked at a RAM
socket, and all voltages were there, and well within specifications.
The problem is, I'm not sure where to go from here. I have NO schematics,
and haven't ever troubleshot a 5150 before.
I DO have a good meter, and a scope (and I know how to use it!)
What would be the first things to check?
The 5150 is a _very_ conventional 8088 design, there's really nothing at
all odd about it.
So, I'd start by checking the power-good line from the PSU. Then the
processor reset line (make sure the thing is not being held in the reset
state). Check the clock signals round the 8284 clock generator. Then
check for activity on the processor address and data pins and the ISA
slot address and data pins. Also check to see if the processor is HALTed,
IIRC some of the early POST tests will execute a HALT instruction if they
fail. I also seem to rememebr that on a 5150 or 5160, you can read out
the POST error code on one of the ports of the 8255, but I would have to
check the details.
You'll need the 8088, etc, data sheets to find those pins, but not the
schemaitcs of the board. I do have scheamtics at least of the 64K-256K
board (which I don't think is _that_ different in areas other than RAM),
but as ever I don't have any way of scanning them.
-tony