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

corey cohen coreyvcf at gmail.com
Sat Feb 10 06:45:12 EST 2018

> 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.    


More information about the vcf-midatlantic mailing list