I’m curious when you say something downstream could be overloading the 5V….
if I’m seeing the drop from 13V to 8.3 at the rectifier when it’s powered on then would it not be something further upstream overloading the 13V before it’s even getting to the 7805 regulator? The voltage is getting pull down before it’s even getting a chance to be regulated to 5V?

Also, since using a DC power supply seems to work fine - 10VDC power supply hits the 7805 and is regulated to 5V. It makes me think it’s something up stream pulling on or at the rectifier.

I don’t...

The 7805 is taking the 8.3VDC that it’s getting from the rectifier and dropping it down to about 4.3VDC so the regulator is doing something - it’s my understanding that it requires at least 9V to regulate to 5V properly.

I don’t know if it’s relevant but in a previous post in this thread I mentioned the only way to get the light on with AC power supply is by touching 2 pins on that chip together.
A correction I’ll make is that the first pin is 4.3VDC not 8.7.
all of the original measurements in this post are crazy numbers because I was measuring AC after the...

I wanted to ask about some new findings before I started ripping apart the power/rf box.

When the NES is powered off and I plug in the 9VAC power supply the bridge rectifier seems to be doing its job. I get 9VAC at the two diagonal AC pins, and I get 13VDC at one of the other pins that I'm assuming is the negative pin. I get 0 volts at the what I assume is the positive pin though. Picture attached.

When I press the power button that 13VDC drops to 8.3VDC

So does that mean the rectifier is working and something else is causing the voltage drop? Or does that...

I ordered a new bridge rectifier... should get in this weekend. I'll comment back when I get that sorted.

I checked the voltage of the power supply by putting one of the meter leads into the barrel and the other on the outside of the barrel. It shows proper 9VAC there.

when testing pins on the actual board I'm using the chassis as ground.

I could absolutely be wrong but I think to test the rectifier I'd have to desolder the power rf box from the main board to get inside to where the rectifier is. As STJ said - that’s not going to be fun to desolder and redo. Though I will say I have more experience with a soldering iron than reading circuit diagrams.

I was...

Sorry if I’m confused.

In previous posts I’ve mentioned voltages with both AC and DC supply options.

the AC 9V supply option is yielding 8.3VDC going into the 7805 NOT the 13VDC it should be.

So do you think the rectifier needs replacement or could something else be causing the mismatched voltages you’re talking about?

So would this be an issue with the rectifier?

10VDC power supply is yielding 9VDC going into the 7805 and 5VDC coming out. If the rectifier is not doing anything this would be about right with roughly 1V drop? I think the 7805 works as long as there is more than 8V going into it and I believe If the rectifier was working then I'd need a ~13VDC supply to compensate, correct?

The AC power supply at 9VAC is yielding 8.3VDC going into the 7850 and 4.3VDC coming out. Which is not right.


I checked that thread as well. Hopefully I don't have to replace that...

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...

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.

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...

Hey everyone.
happy to join the community. Long time tinkerer. I've always liked taking things apart and seeing what's going on inside of electronics and toys. I enjoy fixing things but often hit road blocks where the issue is beyond my knowledge.
Hoping to find a community here to learn more, find and provide help with projects.