NESessity v1.3 PCB Assembly Guide

To assemble the NESessity PCB you will need:
•	NESessity v1.3 motherboard and power + A/V board
•	All Digikey parts listed in the B.O.M. (included with the kit option)
•	NES donor system: all case components and power / reset button PCB are reused, in addition to the CPU and PPU (picture processing unit) from the original motherboard.

The following components must be de-soldered from the original NES motherboard:
•	The 40 pin CPU and PPU ICs
•	5 pin power / reset connector (large blue connector)
•	Crystal:  Mouser part # HC49US-21.47727-MABJ-UB for the correct NTSC crystal, but there are no suppliers of new PAL compatible crystals

(Optional) one of these add-ons for improved video output:
•	NESRGB by Viletim adds RGB, s-video, composite:   https://etim.net.au/shop/shop.php?crn=203&rn=522&action=show_detail
•	IGR by Borti and Voltaire adds features to the NESRGB:  https://voultar.com/index.php?route=product/product&product_id=80
•	Hi-Def NES by Kevtris adds 1080p HDMI video:   https://www.game-tech.us/product/hi-def-nes/

The NESessity can be assembled as a NTSC console or a PAL compatible console depending on the CPU / PPU chipset and crystal. The NESessity has no region lockout so this only affects CPU speed, sound frequency, and video output. A NESessity system built with the PAL chipset may be incompatible with some Famicom accessories.

NTSC (North America, Japan)
•	CPU:	RP2A03 (original) or UA6527 (clone)
•	PPU:	RP2C02 (original) or UA6528 (clone)
•	21.47727 MHz crystal

PAL (Europe)
•	CPU:	RP2A07
•	PPU:	RP2C07
•	26.601712 MHz crystal

Note: Using the clone chips may be cheaper and easier, but I do not recommend them. Compatibility is poor and there are sound glitches.

Be careful when desoldering CPU and PPU chips from a Nintendo system, as the NES PCB does not have thermal traces on the ground pins and these require extra heat to desolder. I simple solder pump removal tool and high wattage soldering iron can be used, but a quality desoldering station will make this job much easier.

There are 4 options for assembling the NESessity's video output circuit:

1. Standard composite video only
This is the easiest way to assemble the NESessity and provides improved composite video output over an unmodified NES system. Using dual wipe 40p sockets is recommended for the CPU and PPU. A single 8p JST connector is used for the connection between the composite power + A/V board and NESessity motherboard.

2. NESRGB installation for RGB, s-video, and composite video output
Installing the NESRGB provides RGB, s-video, and composite video output. Component video output can be added with an optional add-on board available from the same supplier. Refer to these instructions for assembling the NESRGB:  https://etim.net.au/nesrgb/installation-nes/

Since clearance is limited, the CPU should be soldered directly to the NESessity PCB and a 40p precision socket soldered in the PPU location.

The extra 5v regulator included with the NESRGB is not needed. The NESessity's 5v regulator can handle the additional current draw of the NESRGB.

Bridge these jumpers on the NESRGB for a NTSC system:  J3, J5
Bridge these jumpers on the NESRGB for a PAL system:   J3, J4, J7
J8 is for selecting sync output type. If you are using a RGB cable with a resistor inline the sync wire, leave J8 open. If your RGB cable has a direct wire connection for sync, solder J8 closed.

When using a 9p mini-DIN Genesis 2 compatible RGB output connector, the red, green, and blue signals must be tapped off the BH7236AF encoder chip on the NESRGB rather than the usual connection points. On the enconder chip, red is pin 23, green is pin 22, and blue is pin 21. There are 5 open solder pads on the NESRGB in an "L" layout; 3 of these are used for the red, green, and blue connections.

When building the NESessity v1.3 with a NESRGB, make sure composite video output is not tied to the NESessity built-in video circuit; this can be done by removing the 220uF capacitor.

The newest no-cut RGB power + A/V PCB has no power relay, so it requires 2 wire connections between the "PWR SW" pads and the NES power switch.
The power switch connection can also pass through the NESessity using the original 5p connector. On NESessity v1.3, there is an exposed trace to ground on the solder side of the NESessity PCB that must be cut (by the "PWR SW" pads.) Then two wire connections can be made between the "PWR SW" pads of the NESessity and the power + A/V board (I recommend 22ga wire.)

The no-cut RGB power + A/V board uses the 8p JST connector to the NESessity motherboard for 5v power and sound. The NESRGB video outputs are connected to the RGB power + A/V board with wires or a 8p JST connector.

Optional IGR mod board for use with NESRGB:
The IGR board allows controller inputs to change color palettes and reset the console.
Installation instructions here:  https://www.humblebazooka.com/2020/10/29/how-to-install-bortis-nesrgb-igr-on-a-front-loader-nes/#:~:text=Start%20by%20soldering%20the%20pin,when%20the%20NES%20is%20reassembled.

Bridge the reset jumper on the IGR in the "LO" position
Locate 4p jumper J1 on the NESessity. Pin 1 of this jumper is on the left side. Cut the jumper trace on the right side, between pins 3 and 4.
Connect a jumper wire from IGR "RO" to pin 3 of J1.
Connect a jumper wire from IGR "RI" to pin 4 of J1.

3. Hi-Def NES installation for HDMI and composite video output
Installing the Hi-Def provides HDMI video output up to 1080p.

Assemble the interposers:  https://www.game-tech.us/hi-def-nes-install-guides-nes-001-front-loader-5-assemble-interposers/
Assembling the system:  https://www.game-tech.us/hi-def-nes-install-guides-nes-001-front-loader-6-main-assembly/

The Hi-Def NES can be powered using its internal regulator (as its installation instructions suggest) or with 5v from the NESessity's 5v regulator. 40p precision sockets should be soldered in the CPU and PPU locations.

4. Nintendo arcade RGB PPU installation for RGB video output
This is an older video mod that requires the RC2C03 PPU from a Playchoice 10 or certain Vs. arcade game PCBs. A RGB video amplifier / driver circuit is required. A 21.47727 MHz crystal is used with this mod.  There are 3 unmarked solder pads under the PPU that can be isolated from ground by cutting the 3 traces on the bottom of the PCB. These can then be wired to the RGB amplifier inputs. Using dual wipe 40p sockets is recommended for the CPU and PPU.

Modification required to the original NES power / reset button PCB:

The LED must be removed and re-installed (or replaced) with opposite polarity to function.

NESessity audio circuit notes:

The NESessity does not mix the 2 sound outputs coming from the CPU chip, allowing stereo sound. Potentiometers allow independent gain adjustment for each sound channel; turning clockwise increases gain. The recommended starting point for audio potentiometer adjustment is midway; channel 2 is weaker and needs to be adjusted with more gain.

Auxiliary sound is input from cartridge slot pin 54 and mixed with channel 1 (left audio). Channel 2 is output to right audio. 

For expansion audio to work with Famicom games, the cartridge adapter must have NES pin 54 connected to Famicom pin 46. A jumper wire can be added if this connection is not present.

Notes on 5v regulator and DB15 expansion mounting:

Before soldering DB15 expansion connector pins, bolt into place using 3mm x 14mm countersunk screws, 1/4" O.D. x 1/4" long nylon spacers, and 3mm nuts.
Before soldering 7805 regulator, apply thermal paste and bolt to the heatsink using 4-40 x 1/2" screw and nut.
The 10uF surface mount ceramic capacitor mounts on the solder side of the power + A/V circuit board near the 7805 regulator on the exposed solder pads.

Famicom microphone circuit notes:

The optional Famicom microphone circuit's sensitivity is adjustable with the "MIC ADJUST" potentiometer. A 0805 SMT or through hole LED installed in the "MIC LED" pads indicates when the sound level is high enough and the microphone input is active. The microphone should be adjusted to flicker rapidly when the desired volume level is reached.

Component substitution:

U2 and U3 have two options: 74HC373 and 74HC139 are in the BOM, but a 74LS373 and 74LS139 can also be used (original NES system uses these.)

Memory chips can be substituted if they have the following specifications: Asynchronous SRAM, 32K x 8 or 2K x 8, parallel interface, 5v, 28-DIP or 24-DIP, .3" or .6" width, compatible pinout. Newer versions of the NESessity have memory chip pinouts labeled on the PCB. Using 2K memory chips requires two lifted pins and jumper wires.

Potentiometers can be substituted if they have the same pin layout and value.

For 5v power, a linear 7805 regulator or a modern switching regulator can be used. Some trimming of the RF shield is required to make room for the large heatsink.

Updated 10/23/21