I a having a problem with my NES. I have verified that I am feeding the nes 5 volts, but when I put a multimeter on the power rails in the NES I get 4.25volts. This does not seem like enough to power the nes. Any ideas?
The 7805 regulates some voltage, but takes some voltage. Pump it from 9V to 35V instead. 9V is what it originally takes.
I actually bypassed the 7805. And am not using the power pack.
If you bypassed the regulator then you need to be sure it's function is replicated by whatever you are using. Otherwise the voltage level is likely to dip under load I believe. 4.25 volts if that is constant actually probably is enough to power the NES. Why are you bypassing the regulator and not using the normal power supply?
I am attempting to convert it to battery power for a portable for my wife for Christmas.
3gengames wrote:
The 7805 regulates some voltage, but takes some voltage. Pump it from 9V to 35V instead. 9V is what it originally takes.
35v is extreme! Max should be 12v or so.
Yep, 35V is not a good idea. It's not just how much the regulator can take, it's also the power dissipation, since it turns the extra voltage potential into extra heat. You'd need a bigger heat sink if you fed it that much.
When bypassing the regulator, voltage spikes could damage the console. Even battery powered stuff normally use a regulator.
Maybe try using a switching/buck converter instead of the 7805.
At this point I am using a bench power supply so spikes are not a concern.
Where are you injecting the 5V through? If you're seeing 3/4 of a volt of voltage drop, it's an obvious place to look.
Anyway, when I tested with just a plain NROM cartridge plugged in, my NES seemed to take about 5V at 400mA or so. How much current is yours taking? If it's noticeably more, the next step is to figure out what's sinking the extra current.
In my tests, the NES seems to run fine at 4V, but color will be off; you might be able to compensate for that with other modifications. (Which would help with battery life, too)
My current testing skills are a little bit rusty, but setting my meter to 20M I receive a reading of .26. So I'm thinking something is a little off. It looks like the system isn't recognizing that there is a cartridge in the slot.
Maybe I need to check it against another NES.
20M ... 20megaohms? 0.26 ... 260kiloohms? I'm not certain what you're measuring.
Maybe treating the NES as a resistor and measuring across its +5V and GND? (with it off of course)
My multimeter is a Heath 2311 I set the dial to 20M/10a in the current portion of the dial. I have not taken the plunge to get a fluke yet.
260mA sounds not too far off for a NES, especially without a cartridge in it.
So it is not seeing the cartridge. Got any suggestions? I disabled the lockout chit by pulling pin 4 out of the chip.
Well, for a first step, try going back to using the 7805 and fussing with it until that works. Leaving a TV plugged into the NES's video out is a good indicator: it'll still display things even if you are undervolting the NES itself. But the RF output won't work without the unregulated +13V line (it's the only thing that won't).
After that... you never answered where you're injecting power into the NES. How are you connecting the benchtop supply's 5V line? You've already implied it's not going through the 7805 (good, that wouldn't work). Where were you measuring 4.25V?
Sorry about that. I am putting the 5 volts in the same place the RF/power adapter put the 5 volts on the pcb. I am getting something on the video out line as well. I have amplified the output signal and connected it to the screen I intend to use.
So right now you've got a stable solid color on that screen, but no games run? Are you sure that power is getting to the cartridge? (What game are you testing with?) Do you have a simple logic tester or frequency counter or anything else that will tell you if a line is alternating? If so, are the various CPU address and data lines changing? (
CPU pinout )
How certain are you that the 5V from the bench supply is accurate? If you measure Vcc around the NES's board, is it 4.25V everywhere, or does it vary? Are there any places where it's noticeably different?
The bench power supply measures 5v off of the Nintendo so I know that is good. The 4.25 is constant. I checked several pins plus the chips, plus the 5v in on the cartridge so I know power is being delivered. I have not yet checked the pcb on the cartridge yet to see if there is current there.
I will check the CPU pins. I do have an oscilloscope 100mhz tektronics that I can check the data lines with. I will do that and let you know what I find.
Ok I probed the address and data lines. There is no oscillation at all on those CPU pins.
I assume the M2 pin still oscillating. (If not, is the 21MHz input still oscillating? It certainly should be if the PPU is still drawing a picture. If 21MHz is still oscillating, and M2 isn't, the CPU has broken).
Do any of them start oscillating again when you hit the reset button? If so, the CPU has crashed. The most likely way this has happened is that at some point it fetched one of the 12 instructions that look like 0x?2, almost all of which cause a total crash. This is almost certainly due to the cartridge not being plugged in correctly.
Going back to the voltage question: you say you inject 5V where it originally came from the RF modulator daughterboard? Which is the middle pin of the five huge pins? Or are you injecting 5V on the daughterboard at the last (rightmost) pin of where the 7805 was? (Are you using a front- or top- loading NES? If the former, the orange wire to the reset button and power LED is immediately connected to the RF modulator's trace: is it 5V there?)
M2 and the clock are both oscillating. So might the cartridge be the issue?
The daughter board has been removed and I am using the middle pin to send the 5volts in. Also this is a front loader nes circa 1988.
The address and data lines should toggle briefly after you hit the reset button. Do they? If so, I agree that the cartridge, or connection to it, is almost certainly the problem. What game are you testing with? I know I tested SMB3 running ok on 4V.
If they don't, does the CPU's /RESET input toggle when you hit the reset button?
If those lines toggle briefly after you hit the reset button, but not on initial power up, your voltage lines take too long to stabilize. Try replacing the capacitor C8 (0.1µF, next to the CIC) with something larger, which will lengthen the power-on-reset pulse.
I am testing with Zelda. I have SMB and Tetris as well. I will check the data lines on reset. Is there any pins I can check on the cartridge itself? Can I do some continuity testing between the CPU pins and the cartridge?
I appreciate all of the help on this. My wife and I love the old 8 bit games. They had to rely on story and not graphics like most modern gaming.
By all means, do test for continuity. Be careful; changing the angle the cartridge is plugged in at will often change whether things make good enough contact.
The pinouts you'll want are here:
http://wiki.nesdev.com/w/index.php/Cartridge_connectorhttp://wiki.nesdev.com/w/index.php/Mask_ROM_pinouthttp://wiki.nesdev.com/w/index.php/MMC1_pinout (for LoZ)
How touchy was the cartridge connector before you started this project? You might consider buying a replacement one.
Sorry I have been gone so long. The links you posted greatly. It turns out that the connector was not making full contact with the cartridge. I got that fixed. Now I am facing a different issue. I think I may have fried something. The NES is now pulling 510mA even without a cart and stops working after a minute.
Carmojos wrote:
I think I may have fried something. The NES is now pulling 510mA even without a cart and stops working after a minute.
Normally I'd have thought you were hitting the 7805's thermal protection, but you removed it.
Well, if it's dissipating 2.5W, it's got to be going as heat somewhere. Which ICs are hot? Or "hottest", as the case may be. (Be careful to not burn yourself figuring that out)
Ok I did build a power circuit with a 7805 to power it off a battery so I threw a large heat sink on it. Still having the same problem. None of the IC's on the NES are getting hot. I wonder if the problem isn't the NES at all, but the lcd display I am using.
Any suggestion on more efficient power regulation? I have seen some buck converters but have no experience with those.
If you're willing a spend a small premium, you can get premade buck converter modules—sometimes even the same size as a 7805.
Adafruit has a few.
Digikey has some too. I don't know which is actually the better price after you include S&H and all other extenuating factors.
If you eventually decide to use LiIon cells for their superior
energy density, you might prefer to start with a boost converter, and boost the 4.25-3.2V out of a single cell up to 5V instead of bucking 6V+ down to 5. Or boost 4.5V from three D cells or whatever; D cells are behemoths with all the good and ill that entails.
But before you spend money on that, it'd be good to figure out why it's turning off. Does it turn off if you put it back on the bench supply? Does it respond to the reset button? The extra watt of power has to be being used
somewhere, and it's almost certainly going to be as heat—maybe the PCB is hot somewhere?
Is the 7805 getting hot? (Where did you get it from? It's conceivable a salvaged one might have a damaged overtemp trigger). Are you powering anything else off it? Is current going into the 7805 equal to the current going out? (Or at least, not more than ~10mA more)
I've been looking at LM2577-based step-up converters
on eBay. About $2 a piece, shipped from China. I also see some
$1 shipped fixed 5V step-up converters (might not have enough current capacity though). There's another driver version they're using, XL6009, but some have said it's not as good (it runs at a higher switching rate, for one, for smaller caps) and it seems only one or two Chinese manufacturers make it. The spec sheet was also not very complete as compared to the LM2577, made my many major manufacturers and with a complete data sheet. Just some things I've been looking into for cheap that might be useful.
The 7805 is getting hot. And I took it out of the equation and hooked up the bench supply again and got the same response.
When I reset it which at this point even resets the lcd screen it works for a minute again. When I probe the video lines while it is off with my oscilloscope the lines look fine and continue to pulse as if they are displaying file. I left it on the bench supply for about 20 minutes and could not find any hot spots on the board.
I picked up the 7805 from a local electronics shop frequented by ITT tech students and other local pros so the part should be good quality.
I have not checked the current going out of the 7805 yet. I will check that tomorrow.
I have a lipoly 12volt sitting around that I have been thing ink about using. I did not thing about a step up. I was not sure they could carry enough current. I will look into the 2577 sounds like an interesting option to keep battery size small.
Carmojos wrote:
The 7805 is getting hot. And I took it out of the equation and hooked up the bench supply again and got the same response.
When I reset it which at this point even resets the lcd screen it works for a minute again. When I probe the video lines while it is off with my oscilloscope the lines look fine and continue to pulse as if they are displaying fine. I left it on the bench supply for about 20 minutes and could not find any hot spots on the board.
So... To make sure I'm understanding correctly:
After about a minute, the screen goes blank? And when the screen is blank, the PPU is still generating NTSC and the PPU address lines are still toggling? What do the data lines return?
But any music playing ... do the notes get stuck? Do the CPU address lines also get stuck?
Does the current change depending on whether the game has crashed or not?
It vaguely sounds like cartridge connection issues again...
Does it always happen at the same point in the game? Does this happen regardless of game? Are the ROMs in the cartridge getting warm? How about the cartridge card edge?
You are going to laugh at this. It turns out the problem was a faulty pot on the video amplifier circuit screwing the video signal up. That explains why all of the data lines continued to operate correctly. Nothing was wrong on the nes side. I got that fixed and now it runs stable.
Now to begin work on the audio circuitry.