Because the console was front loading, the controller cables had long wires and connected in the front of the system, it could fit conveniently on a middle shelf of the TV stand or in a compartment of entertainment furniture. Moreover, it was highly convenient that the RF switch was autoswitching, you did not have to fiddle with the TV/Game switch to turn the NES on and off. Finally, for buyers with nice TVs, the NES came with RCA output jacks for video and audio output. AV jacks were pretty much introduced with VCRs in home consumer electronic equipment and the NES tried to look like and function like a VCR, which were front loading.
I do not believe it can be known how much these features helped earn the NES sales. I am rather inclined to believe that the quality of the games like Super Mario Bros. did far more to persuade customers to buy a NES than its modern design. Nintendo produced millions upon millions of the NES-001 from 1985-1993. Of the 34 million consoles sold, at least 33 million were of the NES-001. I would suggest that only a million of the NES-101 Top Loading model were sold. The front loader is much cheaper than the top loader, far more common and does not require any kind of modding to obtain decent video quality.
Many people tend to avoid the front loader because of the cartridge connector. The cartridge connector uses a spring and latch mechanism to get the cartridge pins to make contact with both sides of the cartridge connector. This was the front loader's only major design flaw, but with some careful maintenance, it should be remediable without having to use cheap 3rd party replacements. 3rd party replacement connectors, with the exception of the Blinking Light Win, may get games to work they typically have a Grip of Death and wear out very quickly. The official connector has a near-zero insertion force mechanism and will not place unnecessary wear on your Game Pak connectors.
In order to keep your Front Loading NES in top shape, here is a list of things to do :
1. Clean both ends of the cartridge connector
2. Clean all cartridges
3. Clean the card edge from the NES motherboard that connects to the cartridge connector
When you clean contacts, use a minimum of 91% isopropyl alcohol. 99% is even better, and you can find it at electronics stores. The 70% stuff contains 30% water, and you do not want to use water on your electronics unless absolutely necessary. Use a Q-Tip and have one side wet and one side dry and scrub those connectors until you see no more black on the Q-Tip. You can also use a pink rubber eraser, but I have rarely found a cartridge that would not yield to alcohol.
Water is OK when you are trying to clean a dirty board, but that is about it. Never use water unless you have the ability to dry it off quickly with a heating element. Nintendo did no one any favors when they told people to use water for the official NES cleaning kit. You can also use Deoxit or a similar electronics contact cleaner for tough cases, but alcohol is cheaper and usually does the job.
NES-specific cleaning kits can be hard to find. For the cartridge connector, it is hard to get to it without a cleaning kit. What I recommend is removing the top cover of the NES and the top RF shielding and the metal bar across the cartridge loading tray. Then use a credit card wrapped around on one edge with printer paper, wet the paper with alcohol and insert it into the cartridge connector. A few little wiggling and bending the pins slightly and remove it. You should see some dirt on the paper. Use a dry piece of paper as well. Keep going across the pin connector until the paper comes out clean. Obviously do not use an important card.
4. Clean your NES interior
Compressed air and alcohol Q-tips usually work well here. You may need some running water for the plastic shells, just be careful around the paper-backed labels if you care to preserve them.
5. Make sure the cartridge tray is firmly screwed in
A lot of use may cause the cartridge tray screws to loosen. This can cause a lack of good contact with the upper pins of the cartridge connector. They should be firmly screwed in so the plastic of the cartridge tray is in contact with the PCB and the spring and latch mechanism works.
If you remove your cartridge tray and try to replace it, you may see a gap between the plastic and the PCB. This means that the cartridge tray has not been inserted correctly. There is a lip on the bottom of the front of the cartridge tray that cannot be resting on the PCB. This prevents the spring and latch from working correctly if you try to screw the tray in all the way. It warps the cartridge tray. It also makes the top shell of the Control Deck not have a proper fit. Wiggle it about and shift the PCB a little until you get a proper fit. The front black plastic of the cartridge tray must sit naturally on the PCB
6. Make sure the cartridge tray is in the up position when you turn off your NES
This saves wear on the spring and latch mechanism and gives your cartridge connector pins a chance to relax.
7. Use Electronics Contact Cleaner on AC Adapter and Controller Ports
If these ports look a little rusty and are not giving reliable contact, spray some electronics contact cleaner to try to remove some of the rust.
Things to avoid :
There are two things that are commonly done which I do not recommend doing. First is to disable the lockout chip.
The lockout chip only takes 4 of the 72 pins of the connector, so if you are getting the blinking light regularly, it is usually a symptom that the cartridge connector is not working very well. If you are getting a solid color on your screen, and you usually will, that indicates that other pins on the connector are not receiving a good connection or any at all. If there is no blinking, only a solid color screen, then the lockout chip is not the problem. Only if you consistently are seeing the game's title screen reset should you consider disabling it.
Disabling the lockout chip solely by cutting pin 4 and leaving it floating may cause the chip to fail prematurely. When that happens, your system will not work. Finally, rare games like the NES World Championships 1990 cartridge hardware require a fully functional lockout chip in the console to work. If you must disable it, try pulling the pin out instead of snipping it off. Then solder the pin to ground on pin 8.
Second, do not try to bend pins unless absolutely necessary. The cartridge connector gives you very little room to work with and you can easily misalign the pins. When this happens, they will bend and not bend back properly. If you bend the bottom set up too much, you will experience a Grip of Death common to cheap replacement connectors. Also, the top set of pins are deeply recessed and getting to them will be difficult.
As far as boiling the cartridge connector goes, my connector is very reliable so I never had to try that extreme method. I believe this method does nothing good for the long term reliability of the connector. Plastics and metals do not like extremes of heat, metal tends to rust with water and the heating and cooling can cause warping. Only a small section of the cartridge connector pin will make contact with the cartridge pin, so I would focus on that area with a cleaning kit or the credit card solution mentioned above.