NESessity v1.3 PCB Assembly Guide

To assemble the NESessity PCB you will need:
•	NESessity v1.3 motherboard and power A/V board
•	All parts listed in the B.O.M. (included with the kit option)
•	NES donor system: all case components, power / reset button PCB, CPU and PPU 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 blue power / reset connector (optional)
•	The old crystal can be reused if a new replacement is not available. Mouser part # HC49US-21.47727-MABJ-UB for the correct NTSC crystal; there are no suppliers of new PAL compatible crystals.

(Optional) add-ons:
•	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. Do not attempt to pry / pull these chips from the original NES motherboard until ALL solder is removed.

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

1. Standard composite video only
This is the cheapest and simplest way to assemble the NESessity. Provides composite video that is higher quality than an original unmodified NES. 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, the on-board composite video circuit is not needed and its output should not be combined with the NESRGB composite video. Do not install the following video components: 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 for the NESRGB.

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.

Optional IGR mod board for use with NESRGB:
The IGR board adds color palette switching and NES reset using controller button combinations. 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
Cut the jumper trace connecting pads RO and RI (above the PPU on the NESessity.)
Connect two wires from IGR's RO and RI pads to the NESessity.

3. Hi-Def NES installation for HDMI and composite video output
Installing the Hi-Def NES 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 exposed traces on the bottom of the PCB. These are the red, green, and blue signals that are wired to the RGB amplifier inputs. Using dual wipe 40p sockets is recommended for the CPU and PPU. Sync is obtained from the composite video out pin.

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

The LED must be removed and re-installed (or replaced) with opposite polarity for the power indicator 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 adjustment point for audio potentiometers is midway.

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 to the adapter if this connection is not present.

Famicom microphone notes:

For correct adjustment, installing the indicator LED is strongly recommended. This installs in the "MIC LED" pads on the NESessity. This can be a 0805 SMT LED on the solder side or a through hole LED.

Sensitivity is adjustable using the "MIC ADJUST" potentiometer. Correct adjustment is achieved if the indicator LED flickers rapidly when you yell into the microphone at the desired volume level.

Composite A/V + power board wiring:

The 8 pin JST cable is all that's needed with this setup.

No-cut RGB A/V + power board wiring:

The 8 pin JST cable provides 5v power, ground, and stereo audio connection.

This board has no built in relay, so the power switch can be done two ways:
1. Wire original NES power switch directly to "PWR SW" pins of the A/V board. The original wires may need to be extended.
2. Locate "PWR SW" pins on NESessity and cut the exposed jumper to ground (located on the solder side of the PCB.) Make sure this pin is completely isolated from ground to avoid a short circuit. Using 2 wires, connect the "PWR SW" pads of the NESessity to the same pads of the A/V board. 22ga - 20ga wire is recommended.

The NESRGB's marked pads, chroma (C), luma (Y), composite video (V), and sync (CS#) are connected directly to the A/V board's labeled inputs.

The NESRGB has 220uF capacitors and 75 ohm resistors in series with the red, green, and blue outputs that must be bypassed for use with a Genesis 2 RGB cable. There are 5 pads in a "L" arrangement near the BH7236 encoder chip on the NESRGB. 3 of these pads are connected directly to the encoder chip's red, green, and blue outputs. These will connect to the red (R), green (G), and blue (B) on the A/V board.

Notes on BOM and component substitution:

BOM components marked with a * are for the Famicom microphone circuit and are completely optional.

U2 and U3 have two options listed in the BOM. NESessity uses a 74HC373 and 74HC139, while an original NES system uses a 74LS373 and 74LS139.

It is possible to use different SRAM chips if they meet the following requirements:
•	compatible pinout (may require lifted pins and short jumper wires)
•	2k x 8  or  32k x 8 memory size
•	asynchronous static RAM
•	parallel interface
•	28DIP or 24DIP package (.6" or .3" width)
•	5 volt