console keeps resetting at random times

Check the Power cable or take another one and check it again. Maybe it's the Resetbutton, so open the Console and check this one, too. Take a Y1 (Triwing) Screwdriver to open it!

https://eustore.ifixit.com/Werkzeuge/Sch...

Could be that the console is not getting sufficient power.

Sometimes the insides of the power switch will corrode over time causing the resistance across the switch to become higher than normal. This would reduce the voltage coming out the other side of it. The power switch for the N64 has legs for 12V and 3.3V power. Check the resistance across both (there will be a silkscreen on the bottom of the board telling you where the traces for the 12V and 3.3V lines are). If it is more than a few ohms, consider desoldering the switch, bending back the metal tabs on the bottom of the switch that hold it together, and cleaning the contacts inside it. This may solve your power issue.

Another possible cause is a bad/corroded solder joint on one of the legs of one of the chips inside the console. When the system runs for long enough, the chips will warm up causing the metal legs to flex slightly with this heat. This may cause a loose leg to break electrical contact with the board. A reflow of the CPU, or RCP (biggest chips with the smallest legs) with plenty of flux, and some new solder may help. If you’re going to attempt this, you should have some no-clean flux, solder wick to clean up bridged pins, and something to take excess solder off your iron, like a brass sponge. Look up techniques for ‘dab soldering fine pitch qfn’, or ‘drag soldering fine pitch qfn’. It is important to be gentle with the pins of these chips, as they are quite easy to bend if using a heavy hand, or an oversized tip on a cheap soldering iron (the included chisel tip on a Weller SP25N would be an example of an oversized tip for this job).

I recently had a problem with my N64. When I turned it on it was totally dead even though the red power light was on. I swapped out the memory expansion for the standard jumper pack and it started, but it kept resetting about every five seconds or so. This really seemed like a power supply problem to me. Fortunately they have the pinout for the power supply marked right on the case of the power supply. The 3.3 volt supply measured right on and the 12v supply was a bit low at 11v. I did measure the supply with it plugged into the console and it came up to almost exactly 12v.

Since the supply measured ok I turned to the internet and went down several rabbit holes with no luck. Still wondering about the power supply I decided to get my scope out and have a look at both supplies. As it turned out both supplies had almost 2 volts of 60 Hz ripple on them.

Scope set to 500mv per division.

I then opened the power supply after buying a gamebit screwdriver on Amazon.

https://www.amazon.ca/Screwdriver-Rojuna...

I noticed the capacitor on the line side of the supply was slightly bulged. This cap is right up against the heatsink for the switching transistor so I suspect it got cooked over time. I bet this is a common failure.

It's not a very common cap as it's a high voltage, high temperature cap in a low profile package. I wasn't able to find one locally so I used what I had. It was a bit of an emergency since my grandkids were here from the other side of the country.

I ran the wires out through the line cord opening to avoid drilling holes in the case. The correct part to order from DigiKey is here. https://www.digikey.ca/en/products/detai...

Hopefully this will help anyone with an N64 that is continuously resetting.