Original NES power issues

[CapLeaker]

Read this: https://www.badcaps.net/forum/troubl...d-no-audio-fix

[CapLeaker]

Yeah, but your second voltage wouldn’t be right. 9VAC x 1.414 = ~13VDC. If you put in 9VDC, then you have to subtract the bridge rectifier voltage drop and you get 8.3VDC. Look at the schematic, it needs 2 voltages, one 13VDC and a 5VDC from the 7805 regulator. That means you’d need a 14VDC PSU, not a 9VDC PSU. An AC voltage through a rectifier is always times 1.414 more on DC.

[sli4]

Thanks for the response CapLeaker!
yeah there’s currently no cart in the machine so I’m not worrying about the 72pin (yet haha).

Up until now I’ve been using the original nes-002 AC power supply and a third party AC. Both rates at 9V 1.3a

The blinking light came on when I tried a 10V 700ma DC power supply (I would not use this long term as its lower a peerage and higher voltage than the NES spec.

on the 7805 I’m reading 8.3VDC on the in and 4.3VDC on the out when using the AC power supply.

using the DC power supply I get 9VDC in and 5VDC out.

[CapLeaker]

Update: I tried a DC power supply and the red light started blinking (no game inserted) when powered on. Could this be a rectifier issue?
…this is beyond my knowledge and I'm learning of these components as I go, but I can probably handle the soldering if needed.

A blinking red light with a cassette can be all kind of things. Mostly it is bad contacts on the 72 pin header

No cassette = blinking red light
What PSU did you use now?

[sli4]

Update: I tried a DC power supply and the red light started blinking (no game inserted) when powered on. Could this be a rectifier issue?
…this is beyond my knowledge and I’m learning of these components as I go, but I can probably handle the soldering if needed.

[CapLeaker]

Chit... wrong NES... hang on. You should have 2 voltages. 9VAC coming in, going through the bridge rectifier, then your get 13VDC and it goes to the 7805 regulator, 13VDC in and 5VDC out. Set your DMM to DC after the bridge rectifer!

[sli4]

I recently turned on my old NES to find the red light won't go on at all. When powered on it shows black bars on the tv and a loud buzz through the tv speakers. Powering it off, the buzz goes away and tv goes back to normal (white snow).

I tested the power supply itself and it is outputting 9V as it should - first two solder joints on the board at the power port show the same.

Here's where it starts getting funky - When powered on, one side of the 7805 voltage regulator is showing 18V and the other is about 8.7V (center 0).

On the big blue connector I get 29V on the Brown (to power button) cable when it's off and 0V on the Red (power button return) cable. Pressing power on, the brown drops to 18V and the red goes up to 18v while the orange (voltage to reset button) goes from 0 to 8.7V, Yellow (power to LED) goes from 0 to 1.8V and the white (Reset button return) goes from 0 to 8.7V. If I hold down the reset button while it's powered on the Yellow (power to LED) goes up from 1.8V to 8.7V. I recall under normal operation the red led light goes off when you press the reset button which probably accounts for the increase in voltage from 1.8 to 8.7 there....

Both leads connected at the LED read 8.7V when powered on.

The 7805 should be dropping it down to 5V but I'm not seeing that anywhere. And I can't figure out where the 18V or 29V is coming from - so this doesn't seem right.

All of this was tested as AC on my multimeter as the power supply is a 9V AC power supply.

Any ideas?

One thing I can rule out is a dead LED as well. When I touch the two pins circled in yellow in the attached photo together the light goes on solid. The first circled pin is 8.7V second is 0v