On 2013 Jul 20, at 12:09 PM, Tony Duell wrote:
Brent Hilpert wrote:
On 2013 Jul 19, at 3:23 PM, Tony Duell wrote:
Brent Hilpert wrote:
I have been reverse engineering the 9830 recently (a couple things
left to clean up in the schematic), and Rob and I are currently
I am sure htere are plenty of other machiens htat need
documentation...
Just what is your point here, Tony?
Simply that the HP9800 series has been reverse-engineered alredy.
There
are plenty of machines that haven't been
Except it's not really that simple. What you're really saying is:
- I'm wasting my time RE'ing the 9830 because you've already done
it.
- My time would be better spent RE'ing something else because
you've already done the 9830.
- I should use your schematic of the 9830 instead of doing it
myself.
I have no interest in your advice or suggestion about how I should
spend my time, or where my efforts would best be expended.
Here are some reasons I did not use your schematic:
- The 9830 was one of the first two computers I used. When I was
using it as a kid I never had the opportunity to examine it
internally. When, thanks to Rob, I recently acquired one, I was quite
interested in going through it thoroughly, and - as tedious and
labour-intensive as it is - I take some enjoyment in RE'ing it.
- I have seen some of your schematics. I expect they are
competently done and reasonably accurate, and may be useful to others
in the absence of anything else. They fall far short, however, of
meeting my standards in areas such as presentation, layout and
functional organisation.
I downloaded your 9830 schematic the other night and took a look at
it. I would have had little interest in wading through 89 pages of
your hand-drawn scratch for a machine as complex as the 9830. I'm not
telling you you should move to CAD or computerised drawing - if you
prefer to hand-draw them that is certainly your preregotive. (I like
hand-drawing schematics for a simple item every now and then, just
for the memory and tactile sense of it). But there are real,
functional, disadvantages to hand-drawing, in addition to other
objective shortcomings of your schematics (absence of IC and
connector pin numbers, for instance), and you have ZERO basis from
which to bitch when somebody else looks at them and says: 'Sorry ..
not interested'.
-
And BTW: there is what appears to be an error in your 9830 schematic.
In the tape drive optical sensor circuit, you have the 18.2K resistor
drawn as a feedback resistor from the output of the 741 back to the
LDR and negative input. In all 4 instances of the circuit I have
seen, the resistor goes to ground rather than the 741 output - half
of a voltage divider with the LDR, not a feedback resistor. The 741
runs open-loop as a comparator.
The only reason I hedge in saying it is an error is because it's
vaguely possible you were working from a different version of the
board, but I'd be somewhat surprised, as the circuit as you have
drawn it is an unlikely design. I also haven't seen the version or
date of the board you were working from recorded in your schematic,
so couldn't double-check against that possibility.
Am I mentioning this just to rub it in? No, but it does make the
point that there can be some practical benefits for a reverse
engineering to be done twice by different people, and at this
juncture I don't mind pointing out your schematics are not perfect.
Do I fault you for the error? Not really, the 9830 is a significant
RE task and an error or two in such a job is not cause for great
condemnation.
It has had the consequence however, that the modifications Rik Bos
made in his 9830 tape drives were unnecessary and the article he
wrote up about it is itself largely in error because it was based on
a false premise.