Dead IBM PC 5150 motherboard - help troubleshooting
jwstephens at msm.umr.edu
Tue Jan 22 21:26:49 CST 2008
Richard Beaudry wrote:
> 6) One thing that seems odd is that the ADxx (Address/Data) lines seem
> "stuck". The scope does not show a waveform, and measuring with a meter
> shows some lines right at +5VDC, some at about +4VDC and some at 0VDC.
> Perhaps the processor is indeed HALTed???
On several of the CPU's if you hold the processor reset, you actually
get the reset vector address out. So on the 8088 8086 80186, you get
FFF0 out. I don't know if 8088 has all 16 lines out, or is multiplexed,
but on the 186 we could troubleshoot a board we had with a 186 on it for
a support processor by setting a flipflop that held it reset, and then
look at the lines with a scope.
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