PCB Kit: Commodore 16 116 64KB RAM Memory Addressing PCB [C16 C116] Modular

Description

Overview
This printed circuit board (PCB) implements a modification for the Commodore 16 and Commodore 116 computers, allowing either to address 16KB or 64KB of RAM.  The PCB installs between the 74LS257 ICs and does not require cutting traces or lifting pins (a common suggestion in other implementations of this modification).  Please review the installation instructions below as this modification requires soldering and desoldering of components from an unmodified/factory-condition computer.
Demonstration and video overview of this PCB:
https://youtu.be/5dnHICcseGI
This listing is for one (1) unassembled 64KB addressing PCB with required headers and hardware.  The replacement 64KB RAM modules are
NOT
included.
Combined shipping is available for multiple purchases.  If purchasing more than one item from different listings, please request or wait for an invoice prior to submitting payment.
Furthermore, please send me a message if you are interested in purchasing more than the listed quantity as I may be able to satisfy the request by using parts from another listing.
The following headers and hardware are included in this listing:
64KB Addressing PCBs
Two (2) female/female Dupont cables, ~30cm in length (random color selection)
Four (4) 8-pin round/precision male headers
Two (2) 16-pin DIP sockets
Two (2) 3-pin male headers with removable jumper
Two (2) 1-pin angled male headers
One (1) 2-pin angled male header
The photos also show an example of a fully assembled PCB, and an example of a fully assembled installation in a Commodore 16 computer.  There is also a photo of the the PCB in its factory condition,
which will be split through the center perforation prior to shipping; each half installs to a different area of the computer.  The perforated edge will be filed and smoothed for tidiness after separation.
PCB Dimensions: 28mm x 21mm
U7 PCB Overhead (relative to TOP): 7.0mm above pins 9-16 (*); 6.4mm below pins 1-8; 3.8mm above pins 1,16 (IC notch); 6.4mm below pins 8,9.
U8 PCB Overhead (relative to TOP): 6.4mm above pins 9-16; 7.0mm below pins 1-8 (*); 3.8mm above pins 1,16 (IC notch); 6.4mm below pins 8,9.
(*) Approximated due to filing of edge.
Two 8-pin ROUND male headers must be installed to the bottom of each PCB, allowing each part to be soldered into the system board or to be installed in a socket; a standard rectangular male header may not fit into the system board so this type is prohibited by the PCB.
Each of the computers in the Commodore-264 series (16, Plus/4, 116) has different clearance between the system board and the bottom of the keyboard, so please evaluate your situation carefully prior to purchase.  I have only verified this modification to install into a riser socket within a Commodore 16, with each 74LS257 IC installed in a socket on the PCB.  In this configuration, the RF shield makes contact with the top of the 74LS257.  That said, the PCB is designed for compactness and should install directly to the system board in both the Commodore 16 and 116 without the need for a riser socket; please verify with above dimensions prior to purchase.
Installation Instructions
System Board Preparation (assumes factory Commodore 16 installation)
Desolder and SAVE both 74LS257 IC modules, marked U7 and U8 on the system board.
Desolder and REPLACE both TMS4416 DRAM IC modules, marked U5 and U6 on the system board.  Replace these ICs with DRAM models 4464 or 41464, 150ns or faster (e.g. NEC D41464C-10).
You may install the new DRAM in a socket or directly in the system board.  NOTE: These modules are compatible with the removed memory, and will continue to provide 16KB of RAM without any further modifications.
Locate the two vias immediately adjacent to the RF modulator and between the cartridge port.  Using a multimeter, verify continuity from pins 21 and 22 of the CPU and the
identified vias.  Solder the 2-pin angled male header into
identified
vias (please see photos for an example).
Alternatively, you may separate the header and install it into two vias below the REV text on the system board that are also connected to the aforementioned CPU pins.  Please use a multimeter to verify continuity prior to any attempted installation.
PCB Assembly and Installation
Solder two ROUND 8-pin MALE headers to each side labeled BOTTOM, along the U7/U8 silkscreen footprints.  These headers will insert into the system board (or installed riser socket) in place of the previously removed 74LS257 ICs.  The U7 and U8 silkscreen on the PCB designates the installation location on the system board.
Solder a 16-pin socket to each side labeled TOP along the U7/U8 silkscreen footprints.  This side accepts the 74LS257 IC that was previously removed from the system board.
Solder the 3-pin MALE header to each of the footprints labelled 8KB/32KB, which control the addressing mode of the 74LS257.  You may use the provided jumper or an external switch to select between modes; the center pin is the COMMON connection and one of the two modes MUST always be selected for proper operation.
Solder the 1-pin angled male headers into the footprints labelled "U2 21" and "U2 22".  These footprints designate the connection point to the previously installed 2-pin angled male header, which connect to pins 21 and 22 of the CPU.  Use the provided Dupont cable to complete the connection between the PCB and installed 2-pin angled header (please see photos for an example).
Ensure that each 74LS257 IC is inserted in the PCB with the proper orientation; note pin 1 on the silkscreen.  Ensure that the PCB is inserted into the system board (or riser socket) using similar markings on the system board as a reference.