Original NES power issues

[sli4]

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 rectifier - because I did not know about the rectifier at that point.

[sli4]

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 know if that’s how it works.

but also - my previous message #19 question stands.
when no power is turned on the proper 13 VDC is showing at the rectifier. So is it the rectifier that’s damaged causing that drop when power is turned on or something else?
man’s should I see voltage at all at the pin I circled in blue?

[CapLeaker]

If you get 13V with the switch off, then you got a problem somewhere else. Not the bridge rectifier. Could be that big cap is bad, something is loading the 13V down (only thing 13V in that Nintendo is the RF section, so just disable it by cutting the power to it). Maybe a bad 5V regulator, etc.

[stj]

so lets do some basic education.

if you have a power supply that uses a heavy transformer - a traditional style,
and you dont have a load on it then it will give a higher output than marked.
when it's got a load it outputs the marked amount.

and you could run the console from a dc supply without issues - probably down to 7v if you use the AV sockets.
read this datasheet - it will be helpfull

[Unspun01]

I do not know if the original poster has solved this problem, but I had an old NES with a power problem years ago. I remember replacing a large capacitor on the mainboard near the AC input. I don't think it was bulged or visibly bad, but was not within spec. It's connected to the bridge rectifier. Test it with a capacitor tester or replace with a new one. Let us know how it goes.

[sli4]

Unspun01 thank you for the reply and I apologize to all that I did not follow up here. Your solve is pretty much what I ended up doing.

I ended up getting a full set of capacitors to do a full recap. The first thing I replaced was that large capacitor and it started working just fine after that. There was no sign of damage on it from my original inspection and testing across the input and out put “seemed” okay. But once I popped it off I could see the bottom did not look right. I would never have seen any issue since it was sitting so tight to the board and had no bulging or other typical signs. For good measure I also replaced the 7805 anyway (but I was working before that.

Not a bad project to solve but I wish I could have figured that out with a meter before removing it and doing so much head scratching.

[Unspun01]

@sli4: Great that replacing the capacitor worked for you also. And thanks for reporting back with your update. Hope this thread helps others. Take care!