Archive of the former Yahoo!Groups mailing list: Homebrew PCBs

On 31 Mar 2016 10:28:53 -0700, you wrote:

>Picked up a bunch of these on ebay. Thought before I spend $400 I might as well see what I get with these and do some trial runs.
>
> http://www.ebay.com/itm/361162323034?_trksid=p2057872.m2749.l2649&ssPageName=STRK%3AMEBIDX%3AIT http://www.ebay.com/itm/361162323034?_trksid=p2057872.m2749.l2649&ssPageName=STRK%3AMEBIDX%3AIT
>
> I have a couple questions. I want to use, if possible, the original artwork provided to builders in 1973. Here is a sample of the mainframe artwork that I posted before:
>
> http://www.swtpc.com/mholley/TV_Typewriter/page_18.pdf http://www.swtpc.com/mholley/TV_Typewriter/page_18.pdf
>
> This is literally all I have to work with, since an original copy of the artwork is impossible to get now. So questions:
>
> Is it dark enough to be usable?

I wouldn't be happy with it, no.

> If not, what would be the best way to get it darker without altering it too much? I tried just ‘paint bucketing’ black onto it in Photoshop but it seeks out the less visible grey tones and ‘thickens’ the traces, and sometimes obliterates the drill holes.

Change the color palette to monochrome, and then use a very fine brush
to cover the holes, that's one way.

> I’m assuming using the toner transfer method I need to print the image in reverse?

No, the dark area is the toner which is transferred directly. These
are fine.

>I assume this image was intended to be used with the presensitized boards, thus it would be printed on clear overhead film and laid on top for exposure.

Nope, not at all.

Taken down to a photo/graphics shot and converted into a negative on
kodalith film, then printed on KPR sensitized boards.

OR

Same process and use a positive acting system, where you coat the
board completely with resist, print the positive pattern, develop it,
then tin plate the board, remove the resist, then use ammonium
persulfate or something that leaves tin alone and eats copper.

So depends on what you wanted.

> What would be the best way to get it to print at the correct scale. On other artwork I’ve seen actual scales (or ruler edges) displayed. For some reason that is not done here. I guess these would have been printed on standard 8.5x11 pages or something as life size. But because these were scanned from pages of a magazine it’s not quite exact (I printed and compared to my ICs). I guess I could just scale it up a percent or so at a time, but I’m thinking there must be a more scientific way.

Take an IC on the board and generate from it a measurement, or use the
board edges as a scale. Then scale it up to the desired size from
that.

> Anything else to consider?

It looks as if the paper when scanned was not completely flat, so that
can be a small problem. If you could find a back issue of the
magazine and then scan from that, it would be a lot better.

Harvey

>
> Thanks guys!!
>
>