[vcf-midatlantic] Any trick to discharging ADM-3A

systems_glitch systems.glitch at gmail.com
Sat Feb 10 10:19:58 EST 2018

One of my "shorter list" projects is laying out a proper Batten & Allen
lower character ROM for the ADM-3A. I've got 50K Batten & Allen pins on
order for various ROM replacement projects. It'll be something like this, a
DS1244 replacement I recently built:


Obviously with EEPROM instead of a battery-backed SRAM :)


On Sat, Feb 10, 2018 at 6:45 AM, corey cohen via vcf-midatlantic <
vcf-midatlantic at lists.vintagecomputerfederation.org> wrote:

> > On Feb 9, 2018, at 10:58 PM, E.M.F. via vcf-midatlantic <
> vcf-midatlantic at lists.vintagecomputerfederation.org> wrote:
> >
> >
> >
> >> On Feb 9, 2018, at 5:34 PM, Ian Primus via vcf-midatlantic <
> vcf-midatlantic at lists.vintagecomputerfederation.org> wrote:
> >>
> >> I just loosen the screw holding the yoke clamped in place so it can be
> >> rotated. Then, turn the monitor on, and rotate the yoke with my hand
> >> until the raster is level. Shut it off, then use your screwdriver to
> >> tighten the yoke in place. Tighten the screw down until the picture
> >> tube implodes, then back it off a quarter turn.  :)   But, seriously,
> >> don't crank it down super tight, just enough to hold it snug.
> >>
> >> When rotating the yoke, don't touch the terminals where the windings
> >> are connected. Those will give you a very painful shock. Avoid
> >> touching the windings themselves if possible - just grab it by the
> >> plastic part.
> >>
> >> Technically, you can loosen/tighten the yoke clamp with the power on,
> >> but there is no reason to, always a chance to drop the screwdriver
> >> into it. Similarly, the windings are insulated with enamel - you can
> >> touch them, but I avoid it because there is no reason to touch them
> >> and any crack or damage in the insulation will certainly be noticed.
> >>
> >> You don't need to discharge the tube unless you plan to disconnect or
> >> otherwise touch that second anode connection. The bell of the tube is
> >> grounded, and the yoke itself is insulated wire on a piece of plastic.
> >> The neck of the tube is just clear glass and has no electrical
> >> properties.
> >>
> >> -Ian
> >>
> >>>
> >
> > Awesome. Thanks for the help! I have to work on making a lower character
> rom next.
> >
> > eric
> >
> For the lower character rom you have some options before you resort to a
> 2716 with an adapter.   The Apple II and earlier II plus used the  same
> character generator and there were lowercase adaption solutions for the
> Apple II where you can get a lower case rom.
> Also if you get a different rom and it’s not mapping correctly, the ADM
> taps the address lines for the lowercase rom from an inverted output and
> uses the regular output for the uppercase rom.  You can tap off the vias
> near the uppercase rom that have all 6 non-inverted address lines or you
> can hide a 7404 underneath the chip in a socket.  Just be careful of
> clearance as you can’t fit too high of a chip stack in that part of the
> board.
> Cheers,
> Corey

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