Original NES power issues

[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!

[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]

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.

[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

[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.

[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?

[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.

[stj]

does the 7805 cook?
it could be a bad 7805, or it could be a part downstream overloading the 5v
also it could be a problem with the caps after the rectifier, but as you tried with dc thats probably fine.

[sli4]

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 mean it is NOT working since that one pin has 0V whether it's on or off.

this seems to be the main problem. Whatever is causing that voltage drop is putting the input voltage to the 7805 lower than its working threshold. So the 7805 is spitting out under 5 volts which does not seem enough to fully power the NES.

[sli4]

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

[stj]

disabled the RF would be an understatement - i think i stripped it out.
my original plan was to go RGB but the arcade version of the gfx chip is stupidly expensive if you find one
i also disabled the protecion chip - or removed it, i cant remember which

[CapLeaker]

Lemme guess… you disabled the RF out section which uses the 13VDC, and use the AV out and the rest of the NES on 5V USBC only. Piece of cake.

[sli4]

I wonder what pints do you use on the power supply as ground reference with your DMM?

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 actually watching that video earlier today. Thank you for sharing it though. It gave me the tip on where to get a replacement without it taking forever and costing an arm and a leg in shipping!

stj that’s a really neat 5V mod. I’m interested how you did it - though I want to keep my NES as close to its original form as possible.

[stj]

the biggest problem for beginners is the power stuff is in the can so you have to desolder the RF block to do work on it.
my nes is now 5v

[CapLeaker]

I wonder what pints do you use on the power supply as ground reference with your DMM?

[CapLeaker]

Maybe search for something like "how to test a bridge rectifier" on youtube.

[CapLeaker]

Sorry if I’m confused.

Yeah, me too. You need that 9VAC 1.3A supply. Like I said, 9VAC x1.414 = ~12.8VDC. You can't have 8.7VDC there with the AC PSU, unless you are using a 6VAC supply

Put your DMM in AC mode, plug the PSU in and check the AC voltage in the barrel. If that is o.k, well maybe there is a problem with the bridge rectifier.

Here is a vid for you to watch: https://www.youtube.com/watch?v=MiKiazW5brI

[sli4]

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?

[CapLeaker]

The rectifier is doing not much, because you feed it with DC!
So either you feed the NES with a 9VAC power supply or you need a 14VDC power supply. The diodes in the rectifier have a 0.7VDC loss, so you should get 13.3VDC, just like when you feed it with 9VAC.

[sli4]

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 chip!
good work with the mod/demod. I have to say I’m pretty new at reading the circuit diagrams. So it takes me a while to figure out everything going on but I do see what you’re talking about with the need for 2 voltages; one in and one out of the 7805. I’m thinking in terms of 3 voltages. The psu input, what should be going into the 7805 and what should be coming out.
Once I get the power situation sorted I’ll make sure the av stuff works too.