Nintendo Entertainment System General Maintenance

NES-001 mainboard (NES-CPU-07) with the power/RF module attached at bottom right

The Nintendo Entertainment System was sold in two North American and European versions: the front-loading NES-001 from 1985 and the top-loading NES-101 from 1993. Nintendo's service guidance for the NES-001 is in its World Class Service technician's workbook and its consumer maintenance leaflet. For fault-finding see Nintendo Entertainment System Troubleshooting Guide.

Identify your machine

NES console types

Model	Cartridge interface	Video out	Lockout chip
NES-001 (front loader)	72-pin zero-insertion-force connector with a spring-loaded cartridge carrier	RF and composite A/V	10NES (CIC) at U10
NES-101 (top loader)	72-pin edge connector, not zero-insertion-force; only 68 positions populated (1-17, 20-53 and 56-72)	RF only, except a small number of factory A/V units	None
Famicom (Japan)	60-pin slot	RF; composite on the later AV Famicom	None

The board revision is printed on the mainboard: NES-CPU-xx on the NES-001 (NES-CPU-07 in the photograph above), and NESN-CPU-01, NESN-CPU-JI0-01 or NESN-CPU-AV-01 on the NES-101. The Famicom has its own page, Nintendo Famicom General Maintenance.

Chip map

Integrated circuits by position

Position	NES-001	NESN-CPU-01 (top loader)
U1	Work RAM, 2K×8 SRAM (LH5216AD-10L, MN4216-20 or CXK5816SPS-15L)	Work RAM, LH5216AD-10L
U2	74LS373	HD74LS373P
U3	74LS139	HD74LS139P
U4	Video RAM, 2K×8 SRAM (same types as U1)	Video RAM, LH5216AD-10L
U5	PPU, RP2C02	PPU, RP2C02G-0
U6	CPU, RP2A03	CPU, RP2A03G
U7, U8	74HC368	SN74HC368N
U9	74HCU04	7805 regulator
U10	CIC lockout, 3193A	Not fitted
+5 V regulator	AN7805, in the power/RF module	U9, on the mainboard with a heatsink

Chip maps from Console5, compiled from boards. Console5's NESN-CPU-01 list omits U4, but a video RAM marked "U4 16K-SRAM (VRAM)" is fitted on the board in the photograph.

On the NES-001, Nintendo puts the power supply section inside the RF modulator module, which "provides all of the operating voltages for the CPU PCB, gamepak and accessory devices". On the NES-101 the regulator is on the mainboard with its own heatsink, which sits close to the rear of the case.

Power supply

NES-002 AC adapter and its rating plate

Both the NES-001 and the NES-101 take the NES-002 adapter. Its plate reads "Input AC120V 60Hz 17W, Output AC9V 1.3A" and "for use with NES Control Deck No. NES-001 & NES-101 only". It is a transformer with an AC output, so measure it on the meter's AC range. With no load its output reads above 9 V; that is normal for an unregulated transformer and is not a reason to discard it. The rectifier, reservoir capacitor and 7805 regulator are in the console.

Supply voltages on the NES-001

Nintendo's control deck schematic prints the voltages at the two connectors that carry power on the NES-001 mainboard.

NES-001 connector voltages (Nintendo schematic)

Connector	Pin	Signal	Voltage
P3 (RF modulator)	1	Video	about 1.45 V DC
P3	2	Audio	about 2.55 V DC
P3	3	Vcc	about 5 V DC
P3	4, 5	PS2, PS1 (supply to the power switch)	about 10.65 V DC
P6 (power/reset switch board)	1, 2	PS1, PS2	about 10.65 V DC
P6	3	Vcc	about 5 V DC
P6	4	Reset	about 0 V DC
P6	5	Power LED	about 3.2 V DC

A 7805 holds its output between 4.8 V and 5.2 V at 25 °C (Texas Instruments' figure for its µA7805C; the AN7805 in the NES-001 is an equivalent part). A +5 V rail outside that range points at the regulator, its reservoir capacitor or the rectifier. The capacitor lists for each power module are on Nintendo Entertainment System Capacitor Replacement Guide.

The 72-pin cartridge connector

The NES-001's zero-insertion-force connector does not wipe the contacts each time a cartridge goes in, as a conventional edge connector does, so dirt builds up on both the connector and the cartridges. A dirty connection gives games that fail to start, corrupted graphics, or a console that resets over and over.

Console5's advice, from examining used connectors:

• Inspect inside the connector for bent, damaged or missing pins before cleaning. Cleaning does not fix damaged pins.
• Clean the connector and the cartridges. Remove the connector from the mainboard and clean the board's contacts and the connector's pins. Isopropyl alcohol works on most; a stronger electronics cleaner works better on a very dirty connector. Metal polishes remove gold plating; do not use them.
• Bending the pins inward raises the contact force, which can restore contact but wears the plating faster.
• Worn-out pins are less common than often assumed: Console5 has seen consoles that held a cartridge locked in for over a decade still working on the original connector.
• The gold plating on original connectors can look rusty. A wipe with clean paper shows real rust as brown or orange marks and dirt as black.
• Aftermarket connectors grip much harder than the original, wear their plating off quickly and make cartridges hard to remove. An original Nintendo connector has a number and the Hoseiden logo moulded into the housing, and its fixing holes are flush with the body. Clean the original, and replace it only if it is damaged.

After any disassembly, reset the alignment between the connector and the cartridge carrier: loosen the six screws holding them, push the connector fully onto the mainboard, insert and latch a cartridge, push it fully into the connector, then tighten the screws and test.

Nintendo's maintenance leaflet says not to touch or blow on the game pak edge connector, to check the open end of a game pak for foreign material before use, and to keep the Control Deck door closed. Console5 notes that blowing does briefly improve contact, but the moisture makes the contamination worse over time.

The blinking power light

A power LED that blinks with a blank or flashing screen is the 10NES lockout chip resetting the console because it could not talk to the matching chip in the cartridge. A dirty connection does this as readily as an unlicensed cartridge. Nintendo's leaflet gives the causes as the game pak not pushed fully in, then dirty connectors. Console5 disables the lockout by cutting pin 4 of the chip marked CIC.

Board sections

Nintendo divides the NES-001 control deck into these sections.

NES-001 control deck sections

Section	Components
Power supply	Contained in the RF modulator. Supplies the CPU board, game pak and accessories, and puts 10 V DC on the RF output
Reset	U10 (CIC), four sections of U9 (7404) and X2
Input	U7 and U8 (40HC368), DA1 to DA4, C26 to C37, BC1, BC2, RA1, RA2
System timing	Q2 and X1; supplies the 21 MHz clock to the CPU and PPU
Display	U5 (PPU), U2 (74373), U4 (VRAM), one section of U9 and part of the RF modulator
Program	U6 (CPU), U1 (WRAM), U3 (74139) and one section of U9

Clocks and test points

The NTSC master clock is 21.47727 MHz, from crystal X1, and goes into the CPU on pin 29. The RP2A03 divides it by 12 for a 1.789773 MHz CPU clock; the PAL RP2A07 divides a 26.601712 MHz clock by 16.

RP2A03 (U6) pins

Pin	Signal
1	AD1 (audio: both pulse channels)
2	AD2 (audio: triangle, noise and DPCM)
3	/RST
20	GND
29	CLK (master clock in)
30	TST (usually grounded)
31	M2
32	/IRQ
33	/NMI
34	R/W
35, 36	/OE2, /OE1 (controller 2 and 1 read enables)
37, 38, 39	OUT2, OUT1, OUT0 (OUT0 is the controller strobe)
40	+5 V

Source: NESdev.

Test-point waveforms from Nintendo's technical training workbook

Nintendo's workbook prints oscilloscope traces for eighteen numbered test points, with volts and time per division for each. Nintendo notes that they are representations: what a scope shows depends on the game and where it is in the program, and the traces were taken running Super Mario Bros. and Duck Hunt. Console5 lists the test points as follows.

Test points

Test point	Component	Pin(s)
TP1	CPU	29
TP2	U9 (7404)	2
TP3	U3 (74139)	14
TP4	U3 (74139)	9
TP5	PPU	21
TP6	U3 (74139)	5
TP7	U7 (40368)	1
TP8	U7 (40368)	2
TP9	PPU	25-30
TP10	CPU	2
TP11	CPU	1
TP12	U9 (7404)	10
TP13	PPU	1
TP14	PPU	23
TP15	PPU	10
TP16	CPU	39
TP17	U3 (74139)	2
TP18	U3 (74139)	4

Things that are not faults

• An NES-002 that reads well above 9 V AC with no load.
• Vertical lines in the NES-101's picture. Console5 lists them as a characteristic of the top loader.
• The TV showing the aerial signal with the console off. The RF switch passes the aerial through until the console's 10 V DC on the RF lead switches it over.
• No sound from some games until play starts. Nintendo's leaflet calls this normal.
• A gold connector that looks rusty (see above).

Cleaning

• Wipe the case with a damp cloth and mild detergent. For yellowed plastic, see Retrobrite.
• Clean the cartridge connector and cartridge edges as above, with the console unplugged.
• Clean controller sockets and A/V jacks with isopropyl alcohol and a soft brush.
• Inside, use compressed air and an anti-static brush. Keep water away from the boards.
• Check the solder joints at the power jack, A/V jacks, controller sockets and the power/reset switch board. Nintendo lists the power/reset switch assembly as a probable cause of four separate faults.

Tools

• Phillips #2 driver. An NES-001 case is held by six 12 mm Phillips #2 pan-head screws.
• 3.8 mm Gamebit, for NES cartridges
• Multimeter with an AC range
• ESD wrist strap and anti-static brush
• Isopropyl alcohol (99 %) and lint-free swabs
• Soldering iron, flux and desoldering braid

See Recommended Tools.

Routine care

Nintendo set no service interval for the NES. Before using a console that has been stored:

1. Check the adapter gives AC on the meter's AC range.
2. Clean the cartridge connector and cartridge edges when games start to need a second insertion.
3. Reset the connector alignment whenever the console has been apart.
4. On an NES-001, look for leaking capacitors in the power/RF module, which has most of the console's electrolytics. On an NES-101 the reservoir capacitor (C13 on the NESN-CPU-01) is on the mainboard beside the 7805.
5. Reflow the joints at the power jack, A/V jacks and controller sockets if faults come and go when they are moved.
6. Keep the cartridge door closed, as Nintendo's leaflet advises.

Related pages

• Nintendo Entertainment System
• Nintendo Entertainment System Capacitor Replacement Guide
• Nintendo Entertainment System Troubleshooting Guide
• NES-001 Schematic
• NOA Independent Servicer Technical Training Workbook
• Capacitor Failure Symptoms