Author Topic: N8 Pro NES Black Static  (Read 1787 times)

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Offline samson7point1

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N8 Pro NES Black Static
« on: February 02, 2020, 01:22 AM »
https://youtu.be/Sxu2uRqKrMI

Just received my N8 Pro NES today and I'm having this really weird issue.  When I first turn the NES on everything looks normal, but after about 20 or 30 seconds these little black streaks start flickering across the image.  It starts off with one or two flickers then gets progressively worse until the whole screen is covered in black static.  This doesn't happen with my original EDN8 or original carts on this Frontloader NES.  It happens whether I load a game or if I just leave it on the menu and don't press any buttons. 

After verifying this only seems to happen with the N8 Pro cartridge I also tried all of the following troubleshooting:
- switched out my Retro Game Cave power supply for an OEM power supply
- wrapped the cart in foil (for a makeshift RF shield)
- upgraded the 7805 with a brand new 2A version
- removed the Blinking Light Win and used the original edge cartridge connector
- moved the NES to a different TV on a different floor of the house

I borrowed a different front-loader NES, popped the N8 Pro into that one and everything seemed to work perfectly.  I was able to play for several minutes I didn't see any hint of black flickering at all.  So the problem is definitely that cartridge with that console, but I'm not sure why.  I've ordered a capacitor kit for the first NES because the fact that it takes a few seconds to start exhibiting the problem is a pretty good indicator that it's a capacitor problem, but while I wait for the kit to arrive, I wanted to ask in case there might be some other known explanation for this.

Does the N8 Pro draw more power than the older model?  If it does that might explain why my NES still works fine with standard carts but not with the N8 Pro.

At any rate, I'll try to update this post after I've re-capped the first NES.

Offline Odin Belmont

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Re: N8 Pro NES Black Static
« Reply #1 on: February 03, 2020, 09:30 PM »
https://youtu.be/Sxu2uRqKrMI

Just received my N8 Pro NES today and I'm having this really weird issue.  When I first turn the NES on everything looks normal, but after about 20 or 30 seconds these little black streaks start flickering across the image.  It starts off with one or two flickers then gets progressively worse until the whole screen is covered in black static.  This doesn't happen with my original EDN8 or original carts on this Frontloader NES.  It happens whether I load a game or if I just leave it on the menu and don't press any buttons. 

After verifying this only seems to happen with the N8 Pro cartridge I also tried all of the following troubleshooting:
- switched out my Retro Game Cave power supply for an OEM power supply
- wrapped the cart in foil (for a makeshift RF shield)
- upgraded the 7805 with a brand new 2A version
- removed the Blinking Light Win and used the original edge cartridge connector
- moved the NES to a different TV on a different floor of the house

I borrowed a different front-loader NES, popped the N8 Pro into that one and everything seemed to work perfectly.  I was able to play for several minutes I didn't see any hint of black flickering at all.  So the problem is definitely that cartridge with that console, but I'm not sure why.  I've ordered a capacitor kit for the first NES because the fact that it takes a few seconds to start exhibiting the problem is a pretty good indicator that it's a capacitor problem, but while I wait for the kit to arrive, I wanted to ask in case there might be some other known explanation for this.

Does the N8 Pro draw more power than the older model?  If it does that might explain why my NES still works fine with standard carts but not with the N8 Pro.

At any rate, I'll try to update this post after I've re-capped the first NES.

If it works fine on the other front loader then it's not the cartridge,but your NES.

Offline samson7point1

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Re: N8 Pro NES Black Static
« Reply #2 on: February 05, 2020, 08:24 PM »
If it works fine on the other front loader then it's not the cartridge,but your NES.

That's one possible explanation, yes but it's not the only one. 

The console doesn't misbehave with any other cartridges so whatever else is true the N8 Pro is doing something differently than the legacy N8 and original cartridges.  Now it may very likely turn out that the capacitors in that NES are on the way out but still working well enough that I only notice issues with N8 Pro because the N8 Pro draws more power (I don't actually know that's it's drawing more power because no one has answered that question yet, but it fits the narrative). 

The other possible explanation is that the NES has some funky hardware revision that doesn't play nice with the cartridge, in which case it would be the cartridge and/or firmware and not the NES that was faulty.  While this is not the more likely explanation, it is certainly not unprecedented.

Online nuu

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Re: N8 Pro NES Black Static
« Reply #3 on: February 05, 2020, 10:49 PM »
The Retro Game Cave power supply seems to be able to supply with 2A. I don't think the pro would need that much unless you have a lot of mods on your NES.

Since the lines happens only after some time I guess something is getting hot and starts to fail. There is nothing in the pro that gets very warm?

Offline KRIKzz

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Re: N8 Pro NES Black Static
« Reply #4 on: February 05, 2020, 11:04 PM »
N8 PRO has low power consumption, may be even less than original N8. It something around 60mA

Offline samson7point1

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Re: N8 Pro NES Black Static
« Reply #5 on: February 05, 2020, 11:15 PM »
N8 PRO has low power consumption, may be even less than original N8. It something around 60mA

Thanks for the clarification, though that makes this even stranger. Is it possible the N8 pro isn't drawing more power by itself but somehow causing the CPU/PPU to do more work and draw more power?  I don't understand why else it would just happen with this one cartridge.

I expect to have the system recapped by the end of the week and I expect that will probably fix this issue but I'll update this thread either way.

Offline KRIKzz

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Re: N8 Pro NES Black Static
« Reply #6 on: February 06, 2020, 02:56 AM »
N8 PRO has low power consumption, may be even less than original N8. It something around 60mA

Thanks for the clarification, though that makes this even stranger. Is it possible the N8 pro isn't drawing more power by itself but somehow causing the CPU/PPU to do more work and draw more power?  I don't understand why else it would just happen with this one cartridge.

I expect to have the system recapped by the end of the week and I expect that will probably fix this issue but I'll update this thread either way.

Peak current during sd and fpga initialization could be larger.

Offline samson7point1

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Re: N8 Pro NES Black Static
« Reply #7 on: February 06, 2020, 03:46 AM »
Just finished re-capping the NES and the problem is still there and it's still just with the N8 Pro - everything else works fine.

I've made another video demonstrating with the original cartridge, the legacy N8 and the N8 Pro to show that everything else works fine.  (Feel free to laugh as I try to free my cartridge from the death grip of the first gen Blinking Light Win connector).

https://youtu.be/nJ2HXyoJ-cM

The only reason I'm using Castlevania III is because I like the game, this happens with any game on the N8 Pro, or even if I just leave it on the menu for a minute.

The reason the video is taken at an angle is so you don't see my face in the reflection, but you can clearly see that there's a completely stable picture with both the original cart and the legacy N8, but the N8 Pro starts flickering right away and just keeps getting worse.

The only mods this NES has are the expansion audio resistor and the Blinking Light Win.  I've tested with these removed and it makes no difference.

If the NES was faulty I would expect to see this problem with other cartridges but I don't.  And I've now tested the N8 Pro with a third front-loader NES and it doesn't show the issue, so it's still just this one NES and only with the N8 Pro.

Offline KRIKzz

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Re: N8 Pro NES Black Static
« Reply #8 on: February 06, 2020, 04:02 AM »
I really have no any ideas so far, i just have nothing to work with. If other users will reproduce such problem also then i will try to ask send me system for tests.

Offline KRIKzz

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Re: N8 Pro NES Black Static
« Reply #9 on: February 06, 2020, 04:21 PM »
 I wonder if you can try to switch little jumper on N8 pcb from 5v to 3v and check if it fix your problem. Seems like you have some soldering skill and equipment if you recaped your system (:


Offline samson7point1

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Re: N8 Pro NES Black Static
« Reply #10 on: February 07, 2020, 02:08 AM »
Awesome!  That totally fixed it.  Thank you!

What exactly is that jumper doing?  I get that the NES has a 5v bus and the N8 chips are probably all 3.3v but I assume that jumper isn't connecting 3.3v chips directly to the 5v bus, or is it?

By the way that board is a freakin' work of art.

Offline KRIKzz

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Re: N8 Pro NES Black Static
« Reply #11 on: February 07, 2020, 03:05 AM »
Awesome!  That totally fixed it.  Thank you!

What exactly is that jumper doing?  I get that the NES has a 5v bus and the N8 chips are probably all 3.3v but I assume that jumper isn't connecting 3.3v chips directly to the 5v bus, or is it?

By the way that board is a freakin' work of art.

No it not connect 3.3v chips to 5v bus. This jusmper switches io levels at the bus transceiver. I found that some NES units has IO levels significantly lower than 5v, actually around 3.8v. May be some units has even lower (like yours supposedly). Furthermore hi signal phases isn't smooth, in such conditions bus communication with transceiver at 5v isn't stable.


Thi is how PPU address bus signal looks like


Offline samson7point1

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Re: N8 Pro NES Black Static
« Reply #12 on: February 07, 2020, 06:09 PM »
Sorry for my ignorance, but I'd like to repeat back my interpretation of what you said to see if I understand it correctly. 

The transceiver in the N8 Pro is essentially buffering the IO between the chips on the cartridge and the PPU and the PPU side of the transceiver expects the logic from the PPU to be ~5v.  For some reason, the I/O coming from the PPU in my NES is closer to 3v than it is to 5v so some of the signals meant to be read as logic high are dropping below the threshold and getting interpred as logic low.  Is this jumper is telling the transceiver to read input signals from the PPU as low as 3v as logic high, or is it telling the transceiver to stop trying to raise the output signal voltage to 5v because the PPU isn't providing enough power to do it?  Or is neither correct and I'm completely off?


If you can tell me which point you're tapping with the probe and what you're using as a test ROM, I may be able to attach my scope and confirm what the logic level from the PPU in my NES is actually at - assuming it is of any interest to you.

Offline KRIKzz

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Re: N8 Pro NES Black Static
« Reply #13 on: February 07, 2020, 07:32 PM »
both input and output in transceiver operates at reduced voltage if you change jumper.
Certain rom does not matter, you can use any. For measurement you can use any ppu address line or WR/RD signals. https://wiki.nesdev.com/w/index.php/PPU_pin_out_and_signal_description