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 two 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 composite video with quality slightly improved over that of an unmodified NES system. This does not require any cutting or modification of the original NES system case. Using dual wipe 40p sockets is recommended for the CPU and PPU.

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/

When building the NESessity with a NESRGB, do not install these composite video amp components: Q2 2N3906 transistor, 100 & 150 ohm resistors, 220uF capacitor.

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

Bridge these jumpers on the NESRGB for a NTSC system:  J3, J5, J8
Bridge these jumpers on the NESRGB for a PAL system:   J3, J4, J7, J8
Be sure to solder the correct jumpers before installing the optional component video out PCB.

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.

The mini-DIN RGB and s-video output connectors that come with the NESRGB can be used with the included mounting PCB. The hole spacing is 0.75 inches and the mini-DIN connectors should be installed in the case before soldering the pins.

In order to use the built in composite video RCA jack, connect the "V" output pin of the NESRGB to the "C" pin on the NESessity with a jumper wire. The "C" pin is located near the power / reset connector in a row of 5 pins.

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. Auxiliary sound is input from the 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 the included B.O.M:

U2 and U3 have two options listed in the BOM.  An original NES system uses a 74LS373 and 74LS139. These can be substituted with a 74HC373 and 74HC139.

Components marked with a * are for the Famicom microphone circuit and are completely optional. There is a LED that indicates when the microphone input is active. This can be a surface mount LED on the solder side or a through hole LED.

For 5v power, a linear 7805 regulator or a modern switching regulator can be used. The large heatsink for the 7805 requires minor trimming RF shield to make room.

Updated 2/2/21