bz wrote in message
98.139...
"N_Cook" wrote in
:

bz wrote in message
98.139...
"N_Cook" wrote in
:

....

not found a www ref specifically to that Compaq DC polarity.
Did just DVM the blue lead back to the mains connector and 1.3M
regular resistance back to mains ground pin, nothing showing on any
other routes.


Some of these supplies use I2C communications to 'tell the computer
about the power supply capabilities'. Without the I2C communications,
the computer may complain that the supply doesn't have sufficient
capacity to charge the computer's batteries.

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bz 73 de N5BZ k

please pardon my infinite ignorance, the set-of-things-I-do-not-know is
an infinite set.

Would a data stream be observable on the third wire from the ps at
switch on and disconnected from the pc or only after a RTS chirp or
something from the pc when connected?

I think that the computer senses when a voltage is present on the power
jack. I think it then asks the supply 'who are you'. If the supply says 'I
am an 85 (or whatever) supply', the computer is happy. If it doesn't reply
or says 'I am a low wattage supply', the computer gives an error message.

I base this on the fact that the error message appears when I plug in my
'broken' power supply to the computer OR when I plug the supply into the
AC, but not when I plug in a 'good supply' although the 'AC/battery
indicator' changes when either supply is connected.












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bz 73 de N5BZ k

please pardon my infinite ignorance, the set-of-things-I-do-not-know is an
infinite set.

Could not that be done totally within the pc
Within a few seconds of connecting and normal loading is ok try maximum load
for a fraction of a second and if undercurrent/undervoltage then display
error message