Improving NES-001 Reliability

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NES 72 Pin Connector Issues

The NES was designed with a ZIF, or Zero Insertion Force cartridge connector. The ZIF design increases the convenience of inserting & removing cartridges, but over time that characteristics that make it convenient contribute to a buildup of contaminants.

In a non-ZIF, normal cartridge connector, the act of inserting and removing a cartridge will lightly scrub the contacts, clearing away a small amount of surface debris and improving the quality of the connection.

Since the NES uses a ZIF connector, this scrubbing effect is minimized. Blowing on the cartridges is a quick fix to improving conductivity, but the moisture from breath can make the problem worse over time.

When the connection is dirty, games will fail to boot, have corrupted graphics, or appear normal but reset over and over again.

Disabling the 10NES: End the blinking forever

Disable 10NES by cutting pin 4

Nintendo added the world's most annoying chip to the NES, called the 10NES, CIC, or NES lockout chip.

The 10NES chip was added an effort to combat unlicensed development (it is not present in the Famicom). When a cartridge is inserted, the 10NES connects to a companion 10NES chip present in the cartridge. If the connection is bad (probably due to a dirty pin connector), the end result is an endless reset loop, evidenced by the power LED blinking on and off.

10NES is most frustrating when the game is basically working, it just keeps resetting for no reason at all. Or, you're happily playing along and someone comes bounding through the room, just enough to disturb the connection inside of the NES, and reset your game.

Disabling 10NES is simple: Locate the IC marked on the board as "CIC", cut pin 4, and done.

About the 72-pin connector

I remember when the NES was new. The cartridge loading system worked effortlessly. Years went by and this was no longer the case, and eventually 3rd party replacement pin connectors showed up on the market. I purchased one, eager to get my NES working properly. I was quite surprised to find out that the replacement connectors tended to have a death grip on the cartridge, which made the removal of 1st party games difficult, and 3rd party cartridges, like Tengen carts, practically required pliers.

Why do they fail? For the same reasons that any normal cartridge connector can fail, with one big difference: The ZIF design limits the natural cleaning / scrubbing action caused by inserting & removing carts in a typical non-ZIF game system.

In a typical cart-based game system, the act of inserting and removing a game gently scrubs the cart contacts. This helps to extend the length of time between necessary cleaning.

In the NES frontloader, there is almost no scrubbing action, which causes contaminants to build up more easily. The cartridges also have an high number of connector pins, increasing the number of potential failure points. The addition of a security chip to the console who's sole purpose in life is to keep resetting the machine should it not find an equivalent chip within the cartridge is just the final icing on the cake.

Aftermarket 72-pin connectors

Used pin comparison: Aftermarket pin on left, OEM Nintendo pin on right
How to spot an aftermarket or OEM connector: Aftermarket pin on left, OEM Nintendo pin on right. The Nintendo connector has a number molded into the housing. The fastening holes are flush with the connector body, as opposed to the aftermarket connector which shows that the holes were machined after molding, or come from a mold with machine marks.
How to spot an aftermarket or OEM connector: Aftermarket pin on left, OEM Nintendo pin on right. The Nintendo connector may have a little symbol cast into the plastic. Again, the holes are flush with the body of the connector housing and don't show drill/machine marks.

Why I hate replacement connectors:

  1. The tension is too high!
  2. The quality is bad all around

Observe the picture of the pins on the right. These two pins came from non-working connectors. They were both cleaned and then extracted and examined. The pin on the left comes from an aftermarket 72-pin connector. This pin is ruined: the outer plating is gone and the oxides that continue to form will probably harm game cartridges. The abrasion due to increased pin tension combined with substandard quality leads to a short life.

The connector on the right comes from a used OEM Nintendo 72-pin connector. The gold and nickel plating is still intact and this unit will probably continue to function normally (the discolored spot at the bend is actually made up of minute surface scratches in the gold, causing the light to refract). Because there is very little resistance in the design of these connectors, there is less abrasion and a higher chance of proper function once cleaned.]]

72-pin Myths

  • But aren't the pins just bent out of shape from years of use?
    • I read this a lot but I'm not convinced. If someone has a sample of cutaway pictures of used and unused pin connectors showing fatigue, I'd love to see them. If the pins were going to bend or settle in, I believe that would have happened within the first year of ownership. I have seen NES units with cartridges inserted & locked in place for well over a decade that still continue to function correctly on the original connector.

It is possible that a device like a Game Genie, or any other accessory that connects to the NES pin connector in an unconventional manner could damage the pins. This could occur if the PCB thickness were excessive, or the insertion angles were incorrect


  • I think they're bent because when I bent them back the other way it started working again.
    • What this does is increase the contact force, which can improve contact quality, but is tedious and may remove some of the ZIF characteristics. It is also difficult to bend 72 split pins in a consistent manner. Increasing the pin tension will also increase abrasion, and may cause the plating to wear through.


  • I removed my old pin connector and it was rusty
    • It's a bit of an optical illusion, but the gold plating used on OEM connectors can have a rust-like appearance. The exception would be a severely worn/damaged connector with a ferrous base metal. A clean paper swipe test should revel actual rust as brown/orange marks, versus normal dirt as black marks.


Pin connector solutions

A lot of solutions for fixing the cartridge connector have come up over the years. Let's start by examining the potential causes of connection problems:

  1. Damaged or dislocated pins on connector, cartridge, or both
  2. Dirty contacts on connector, cartridge, or both
  3. Poor cartridge to pin connector alignment


Damaged or dislocated pins on connector, cartridge, or both

  • Inspect, repair, or replace

All the cleaning in the world won't fix damaged contacts, so before beginning a cleaning procedure, visually inspect the inside of the pin connector for pins that are bent, damaged, or missing. If they aren't extremely bent or damaged, they can be bent back into shape. For pins on the outer portion of the connector, it may be easier to remove the damaged pin and repair it outside of the connector housing.

Likewise, damaged cartridge contacts can be repaired using circuit repair pens, trace repair kits, etc., but the scope is beyond this document. If the damaged contact is outside of the pin connector contact zone, a small jumper wire can be soldered over the break.


Cleaning Dirty Contacts (simple, non-aggressive)

  • Use cleaning kit to clean pin connector
  • Clean cartridge contacts


Before replacing any parts, these steps should not be overlooked. I would suggest the Nintendo-brand NES cleaning kit. It is designed in such a way that it makes very good contact with the pin connector during cleaning. I've tried some of the 3rd party kits and have not had as much success.

Most, if not all cleaning kits use a solution that is mostly isopropyl alcohol. Isopropyl alcohol is a decent cleaner, but if the pin connector is exceptionally dirty, it won't have a very substantial effect. A strong electronics cleaner will have a more noticeable impact. There are a few brands available, and even some DIY recipes.

Don't forget to remove the pin connector from the main PCB and clean those contacts, too! Both on the PCB and on the pin connector.

Most NES cartridges have gold-plated connectors on the card edge, and should be oxide free (unless the plating is worn or damaged). Cleaning with alcohol and cotton swabs is usually sufficient, unless the cartridge has had a particularly rough life. Very dirty cartridges should be disassembled and cleaned. Stubborn crud can be removed with a very mild abrasive, such as an art eraser (not a pink pencil eraser!). Always follow up with another alcohol / cotton swab treatment. Metal polish liquids will remove the gold plating. Do not use polishing liquids, like brass / copper cleaners, stove top polish, etc.


Cleaning Dirty Contacts (slightly more aggressive)

  • Bend pins to increase contact force

Not my preferred method, but it has worked well for others. The idea is to form a tool from a piece of wire, like a paperclip, and bend each pin further toward the cartridge surface. This may accelerate wear of the plating.


Cleaning Dirty Contacts (highly aggressive, last case scenario)

  • Use sandpaper to aggressively remove corrosion from pin connector

Years ago, I used to recommend this. Now that I've really examined the connectors, there's no way I can recommend this procedure. It may temporarily bring back function, but will absolutely destroy a connector in the long term.


Optimizing Pin Connector to Cartridge Alignment

  • Reset pin connector alignment

If your NES has been disassembled at some point, as many of them have been, you may have a slight alignment problem between the pin connector & cartridge caddy (that spring loaded deal that the cartridge slides in to). There is some play in the alignment of this entire mechanism. If the alignment is a few degrees off, contact quality can suffer and cause inconsistent operation.

Follow this simple procedure to reset the cartridge alignment whenever the NES is disassembled for service.

  1. Remove the upper case from the NES
  2. Remove the upper RF shield
  3. Loosen the 6 screws holding the 72-pin connector and caddy
  4. Push the 72-pin connector fully onto the main PCB
  5. Insert a cartridge and latch it into the downward position
  6. Push the cartridge fully forward into the pin connector
  7. Tighten the 6 screws holding the pin connector
  8. Bench test the unit to make sure that everything functions
  9. Replace the upper shielding, and upper case

I've had NES units that were cleaned top to bottom, including refurbished pin connectors, that still worked intermittently. In many cases, resetting the alignment was like giving them a personality transplant, bringing reliability back.