Mac 512 video mods

From: Phil Beesley <>
Date: Thu Jul 16 11:21:02 1998

Yesterday I acquired two boxes, each about the size of a UK telephone
directory, that were described as "AppleTalk to serial convertors".
Opening them up reveals a Mac 512 motherboard, a nice Farnell psu,
and a homebrew card in place of Apple's analog board. There are a
couple of other mods such as the programmer and reset
switches mounted on the front panel, small speaker mounted inside the
case, no internal floppy, keyboard extender.

The Mac board in box #1 appears to be completely standard. The
homebrew board contains 2 * SN74LS221N and 1 * 74LS256N with a lead
joining it to a composite connector. Does anybody have any idea what
the video output might be for? I understand that there were a number
of homebrew video mods of this type published in Mac magazines in the
mid 80's.

The Mac board in box #2 appears to be slightly non standard. At the
location F3 the original SN74F253N has been piggy backed with a
7F153PC (I think). There are also a few connections to the chip at
location F2 and to a factory solder pad on the motherboard. The
homebrew board looks similar to that in box #1 but is better made and
clearly hand labelled "composite video".

Which size floppy drive should these boards support? The ROM HI is
Apple # 342-022 and ROM LO is # 342-0221.

Any thoughts,

Phil Beesley -- Computer Officer -- Distributed Systems Suppport
University of Leicester

Tel (0)116 252-2231
Received on Thu Jul 16 1998 - 11:21:02 BST

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