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Jailbars on a front loader - help required
http://forums.nesdev.com/viewtopic.php?f=2&t=16607
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Author:  romibraman [ Wed Oct 25, 2017 3:50 pm ]
Post subject:  Re: Jailbars on a front loader - help required

lidnariq wrote:

You can flip the super-simple schematic over to use a PNP transistor:

.



Gosh I so dumb... I did not run a wire from the 5v to E... you bet it did not work...

Can I go to PPU pin 40 or should I go directly to The 7805 ?

I will get my hand on a 33r and a 220r and try again tomorrow

Author:  lidnariq [ Wed Oct 25, 2017 4:32 pm ]
Post subject:  Re: Jailbars on a front loader - help required

Whatever's easier to get a wire to. Doesn't matter much.

Author:  romibraman [ Thu Oct 26, 2017 2:08 pm ]
Post subject:  Re: Jailbars on a front loader - help required

Ok update of the day.

I have been able to recreate the composite signal on the breadboard. It was not perfect, the color were off, but the jailbars were still clearly there. Not as visible than on the original RGB signal, but exactly the same pattern.

So I guess we can rule out the corruption of the video signal after the PPU

So what do we have left ?

PS : I also changed the CPU... same result.

Author:  lidnariq [ Thu Oct 26, 2017 2:37 pm ]
Post subject:  Re: Jailbars on a front loader - help required

The next thing I'd try would be isolating the PPU onto its own independent power supply.

Author:  romibraman [ Thu Oct 26, 2017 2:46 pm ]
Post subject:  Re: Jailbars on a front loader - help required

lidnariq wrote:
The next thing I'd try would be isolating the PPU onto its own independent power supply.


Interesting, so I lift Pin 40 and use another 5V supply ?

Should I isolate the ground too (pin 20) ?

Author:  lidnariq [ Thu Oct 26, 2017 2:54 pm ]
Post subject:  Re: Jailbars on a front loader - help required

No, ground needs to be tied so that digital signals can be communicated in and out of the PPU.

Author:  romibraman [ Thu Oct 26, 2017 2:58 pm ]
Post subject:  Re: Jailbars on a front loader - help required

lidnariq wrote:
No, ground needs to be tied so that digital signals can be communicated in and out of the PPU.


Ok so just an external 5v supply directly to pin 40. Thanks, that will be tomorrow’s episode.

Author:  romibraman [ Thu Oct 26, 2017 3:19 pm ]
Post subject:  Re: Jailbars on a front loader - help required

lidnariq wrote:
No, ground needs to be tied so that digital signals can be communicated in and out of the PPU.


Just to make sure, I need to wire the ground of external 5v supply to the common ground of the NES PCB right ?

Author:  lidnariq [ Thu Oct 26, 2017 3:26 pm ]
Post subject:  Re: Jailbars on a front loader - help required

Yeah, ground needs to be tied together somewhere.

Author:  FrankenGraphics [ Thu Oct 26, 2017 3:44 pm ]
Post subject:  Re: Jailbars on a front loader - help required

If the PSU is causing switching noise via EMC effects, high enough to appear in the video field repeated times per frame or even line, shouldn't a ferrite bead in the right spot help filter it out? Might be worth trying, considering they cost nickels.

Author:  lidnariq [ Thu Oct 26, 2017 4:10 pm ]
Post subject:  Re: Jailbars on a front loader - help required

Yeah, the right way to fix the +5V rail if it is the problem probably involves an L+C filter.

Author:  romibraman [ Fri Oct 27, 2017 8:01 am ]
Post subject:  Re: Jailbars on a front loader - help required

lidnariq wrote:
Yeah, the right way to fix the +5V rail if it is the problem probably involves an L+C filter.


Ok.....

So pin lifted, external power supply, a totally different 7805, everything grounded and...

Same thing. The image was slight distorted, i probably needed a few more caps in there, but I could still see the jailbars with the same pattern as before.

At this point I should probably give up but it’s really annoying not to even find the root cause of the issue.

If you have any other idea, my iron is still warm :-)

Author:  lidnariq [ Fri Oct 27, 2017 11:59 am ]
Post subject:  Re: Jailbars on a front loader - help required

romibraman wrote:
Same thing. The image was slight distorted, i probably needed a few more caps in there, but I could still see the jailbars with the same pattern as before.
Right, that's the big problem.

The jailbars that you showed are because it is the PPU itself that simultaneously drives both PPU A13 and the analog video output. (Probably. I think we've eliminated the capacitive coupling option?)

The power supply needs to be a lot firmer (more capacitors, with less ESR, a mix of both ceramic and electrolytic, shorter wires) to reduce the amount of visible jailbars.

Perhaps try moving the place where you supply the extra bonus 5V supply across the PPU's power and ground pins (if it's further away)

Author:  romibraman [ Sat Oct 28, 2017 3:25 am ]
Post subject:  Re: Jailbars on a front loader - help required

lidnariq wrote:
Right, that's the big problem.

The jailbars that you showed are because it is the PPU itself that simultaneously drives both PPU A13 and the analog video output. (Probably. I think we've eliminated the capacitive coupling option?)

The power supply needs to be a lot firmer (more capacitors, with less ESR, a mix of both ceramic and electrolytic, shorter wires) to reduce the amount of visible jailbars.

Perhaps try moving the place where you supply the extra bonus 5V supply across the PPU's power and ground pins (if it's further away)
The jailbars that you showed are because it is the PPU itself that simultaneously drives both PPU A13 and the analog video output. (Probably. I think we've eliminated the capacitive coupling option?)

The power supply needs to be a lot firmer (more capacitors, with less ESR, a mix of both ceramic and electrolytic, shorter wires) to reduce the amount of visible jailbars.

Perhaps try moving the place where you supply the extra bonus 5V supply across the PPU's power and ground pins (if it's further away)[/quote]

Ok I’ll have fun with capacitors

What do you recommend for capacitors values ?

All of them between the external 5v lines and the common ground ?

Thanks again man, you’ve really been a great help.

Author:  lidnariq [ Sat Oct 28, 2017 12:20 pm ]
Post subject:  Re: Jailbars on a front loader - help required

The big thing I'd look into would be minimizing ESR? So maybe a 100pF ceramic, a 100nF ceramic, and some electrolytic with a low ESR? all as close to the PPU power pins as possible.

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