31 Aug
2011
31 Aug
'11
12:12 p.m.
Yes, that's the one. It was fairly expensive, but
I've never worked on a
US-market II+ before, so I was very keen to have a look, see how different
it is to the Europlus. As it turns out (and as I already knew second-hand),
there are very few differences indeed. One difference appears to be that
the original US market PSU is shorter than the Europlus one that was fitted
From what I rememberm the PSUs are actually Astec
units. The scheamtic
shown in the reference manual doesn't match the PSU in my
Europluses, but
then again it's very psosibl that several versions of the PSU were used
over the years.
when I got it. Whoever changed it just pulled the
speaker from where it was
glued to the base in order to give enough room for the new PC, leaving the
speaker floating around loose inside the case... during shipping...
grumble. For all I know, impact damage from this has caused any number of
extra faults! It broke one of the legs off the clock crystal, for a start.
ARGH!.
When I wsa sortign out my (totally dead) HP9820, one of the first checks
I did after ensuring all the PSU rails were correct was the clock
circuit. This starts with an 8MHz crystal oscillator. Checkign the output
of this circuit (a couple of TTL gates, some R's and Cs, and the
(socketed) crystal) showed a very distoete waveform at aobut 20MHz. This
remained the smae when the crystal was unplugged, and was acutlaly just
the natural osciallation frequencyt of one of the gates with a resistor
linking output to input. Fitting a good crystal got it back at 8Mhz.
Intrigued, I carfully cut the can off the defective crystal to see that
the quartz (?) plate inside was acutally broken in half (there's a
picture of it in mu flickr account). I asuem this must have happend when
the machine was dropped or something.
-tony