30 Jun
2008
30 Jun
'08
12:17 a.m.
Sellam,
[Top answering, since inline is getting a bit long].
My fix to the array of dots the monitor was to build the Obtronix Apple-1 correctly! The
problem was I accidentally swapped two resistors. On
board location D1 (upper left near video connection) R1 should be 1500ohm and the 6
resistors at C2 should be 7500ohm. I had swapped R1 with one of the 6 resistors at
location C2 (I don't think the location C2 resistors will cause dots since these are
pull-down resistors). I had mixed up a brown with violet, swapping a 1500 ohm resister
(brown-green-red) with a 7500 (violet-green-red).
Not being a circuit guy (be nice, y'all) my mistake kinda made sense. If I remember
my research correctly, pulses from the character generator and the sync signal generator
are "combined" through R1, 1500ohm (for char gen) and R2, 3000ohm (for sync),
meeting at the base of the video drive transistor. R1 and R2 *should* have a 1:2 ratio.
My mistake (ie wrong R1) made it backwards and 2.5:1. The char gen pulses amplitude was
less than it was supposed to be. Crank up the contrast to see the characters better and
you start seeing sync residuals aka dots.
Mind you, my analysis may be off.
Do you have a way to contact Yumoto Hirohisa? I'd still like to pass on this
information.
BTW regarding Apple-1 photos, I was hoping someone would have copies of those at
http://homepage2.nifty.com/56thWAREHOUSE/HAJIME.html
Thanks,
Scott
----- Original Message ----
From: Sellam Ismail <sellam at vintagetech.com>
To: Scott Austin <us21090 at yahoo.com>
Cc: cctalk at classiccmp.org
Sent: Friday, June 27, 2008 5:32:10 PM
Subject: Re: Apple 1 on eBay
On Fri, 27 Jun 2008, Scott Austin wrote:
Why? In the photos of the monitor attached to the
Apple 1, I recognized
a video problem that I ran into when I built my Repro Apple 1. It's an
array of small dots across the entire monitor screen. I wanted to
contact the owner to provide my bit of insight on the problem.
Interesting! I too saw this issue on an Apple-1 I brokered a couple years
back. If you turn down the contrast or something it seems to go away.
What is your fix?
Does anyone know the Japanese owner(s) of Apple
1('s)?
I have one in my registry. He bought the first Apple-1 I brokered in 2000
(at VCF 4.0).
At one time I only had the last name of an owner who
had two Apple 1's.
Could it be him?
This particular Japanese owner has two, so maybe/probably. His name is
Yumoto Hirohisa. This is public knowledge, by the way, his story having
been written about in Christine Finn's book, _Artifacts: An
Archaeologist's Year in Silicon Valley_.
Does anyone have photos of a Japanese owner with his
Apple 1?
In fact, there's one in the book :)
I have extra copies available for sale or trade (I think they cost me $20
or so).
--
Sellam Ismail Vintage Computer Festival
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