Undesired Jail bars on French NES and checkerboard pattern

Discuss technical or other issues relating to programming the Nintendo Entertainment System, Famicom, or compatible systems.

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tepples
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Re: Undesired Jail bars on French NES and checkerboard pattern

Post by tepples » Mon Jan 20, 2020 6:20 pm

If the goal is to ensure a stable power supply by using a bypass cap to inject extra current as needed, having caps that are about the same value is probably OK.

psycopathicteen
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Re: Undesired Jail bars on French NES and checkerboard pattern

Post by psycopathicteen » Mon Jan 20, 2020 8:35 pm

I wonder why the French NES didn't use a PPU that outputted an RGB palette.

lidnariq
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Re: Undesired Jail bars on French NES and checkerboard pattern

Post by lidnariq » Mon Jan 20, 2020 9:44 pm

alfredocalza wrote:
Mon Jan 20, 2020 3:48 pm
Unfortunately, I do not have an oscilloscope. Are they too expensive?
They're not too bad anymore ... for this purpose a cheapo USB one should be fine, e.g. https://sigrok.org/wiki/YiXingDianZi_MDSO or https://sigrok.org/wiki/Hantek_6022BE (~$50-$60).

You can pay a little more (~$200-$300) for a substantially better one (1 GSa/sec, 60-100MHz).

All are a little silly for a one-off investment.

... hm. you might be able to use a USB capture card that accepts baseband PAL?
Do you think that doing something like this on my french NES is worth a shot? I already tried the tantalum caps in the range of 10 to 45 uf on the 5v input of the PPU and that did nothing on the jailbars.
May as well try...
psycopathicteen wrote:
Mon Jan 20, 2020 8:35 pm
I wonder why the French NES didn't use a PPU that outputted an RGB palette.
That requires custom silicon, and the French (and USSR/former USSR) market wasn't worth it to N. But it was worth it to UMC.

alfredocalza
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Re: Undesired Jail bars on French NES and checkerboard pattern

Post by alfredocalza » Tue Jan 21, 2020 7:25 am

I think I am going to skip the oscilloscope part for now and try to see if I can figure this out without it. I read that the cpu-11 board was the most problematic in terms of unwanted interference. I will try to compare all traces on this board with those on my other cpu-07 board to see what the differences are. For what I can remember, there were not really any differences on the traces near the ppu. However, there were substantial differences in the traces around the cic. The cpu-11 also has a bunch of diodes near the cic that the cpu-07 doesn't have. Could any of this be causing any interference on the video line or ppu?

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Re: Undesired Jail bars on French NES and checkerboard pattern

Post by lidnariq » Tue Jan 21, 2020 11:26 am

... I forget, have you disabled the CIC? If so, how?

alfredocalza
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Re: Undesired Jail bars on French NES and checkerboard pattern

Post by alfredocalza » Tue Jan 21, 2020 4:02 pm

lidnariq wrote:
Tue Jan 21, 2020 11:26 am
... I forget, have you disabled the CIC? If so, how?
Well I didn't, the previous owner did. He just broke one of the CIC's pins off. He did not even connect the pin to ground; instead he just ripped it off from the CIC. I always wondered if this had something to do with the jailbars or pattern.

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Re: Undesired Jail bars on French NES and checkerboard pattern

Post by lidnariq » Tue Jan 21, 2020 4:05 pm

Well, the checkerboard pattern might be from the CIC. The jailbars won't be.

You could try using the "two wires" CIC mod: viewtopic.php?p=209346#p209346 - it'll keep the CIC's clock from running, and the CIC's clock is about 4 MHz, so that could also be consistent with the output.

alfredocalza
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Re: Undesired Jail bars on French NES and checkerboard pattern

Post by alfredocalza » Wed Jan 22, 2020 12:32 am

lidnariq wrote:
Tue Jan 21, 2020 4:05 pm
Well, the checkerboard pattern might be from the CIC. The jailbars won't be.

You could try using the "two wires" CIC mod: viewtopic.php?p=209346#p209346 - it'll keep the CIC's clock from running, and the CIC's clock is about 4 MHz, so that could also be consistent with the output.
Thank you! I'll try this today when I get back home. The checkerboard pattern is a big issue for me; it doesn't look good at all.

It is still very strange to me that this console has jailbars, but the CPU-07 doesn't. I have looked at the board and everything around the PPU and around the composite video out line seems to be the same in both consoles. The major differences are around the CIC with two additional diodes and two additional resistors and different traces around it on the CPU-11.

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Re: Undesired Jail bars on French NES and checkerboard pattern

Post by alfredocalza » Wed Jan 22, 2020 2:39 pm

Nope, unfortunately, it did not work!

Some pictures here:

Here is the sync separator I built:
IMG_20200122_212730.jpg
IMG_20200122_212825.jpg
Here is the CIC mod:
IMG_20200122_212717.jpg
...And here are the same old results :(
IMG_20200122_212309.jpg

lidnariq
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Re: Undesired Jail bars on French NES and checkerboard pattern

Post by lidnariq » Wed Jan 22, 2020 3:03 pm

Well, looking more closely, the period of the checkerboard pattern is definitely some residual from the chroma signal. (There are 27 dots in the same time that it takes to emit two [?] blocks, so that's roughly 4.49MHz ± .09MHz, and PAL chroma is at 4.43MHz)

But without better diagnostic tools, I really can't help any further. Especially as long as you're reliant on the V7021.

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Re: Undesired Jail bars on French NES and checkerboard pattern

Post by alfredocalza » Sat Jan 25, 2020 5:33 am

I think I'm gonna end up buying an oscilloscope; I could just buy another NES for less money, but I just will not be able to rest until I find where the interference is coming from.

Talking about frequencies (which I do not know much about lol), What does the 26,06 mhz crystal on the nes motherboard do? It has a 18pf capacitor and a trimmer. The modulator had a 4,4 mhz crystal which I already replaced and adjusted, and which did not make a difference on jailbars or checkboard pattern. But what does the other crystal on the motherboard do? I have some spare crystals with the same frequency that I could replace it with (left overs from when I did my SNES 50-60hz multi region mod).

alfredocalza
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Re: Undesired Jail bars on French NES and checkerboard pattern

Post by alfredocalza » Sat Jan 25, 2020 6:29 am

Forget abut it. I just checked and I only have 17 and 21 mhz crystals, but not 26 mhz ones.

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Re: Undesired Jail bars on French NES and checkerboard pattern

Post by alfredocalza » Sat Jan 25, 2020 7:52 am

Lol, I started to mess with the 26mhz crystal trimmer on the board and broke the image. Now there are strange moving horizontal lines across the picture with different colours and cannot get the image back to what it was, even if I adjust the trimmer back in the same position as before. I think I might have broken the crystal or the trimmer!

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Re: Undesired Jail bars on French NES and checkerboard pattern

Post by lidnariq » Sat Jan 25, 2020 12:34 pm

alfredocalza wrote:
Sat Jan 25, 2020 5:33 am
I think I'm gonna end up buying an oscilloscope; I could just buy another NES for less money, but I just will not be able to rest until I find where the interference is coming from.
Something that acts like a TV that accepts PAL baseband may be a cheaper option, such as a composite-to-USB adapter.
What does the 26,06 mhz crystal on the nes motherboard do?
"Everything".
It's divided by 6 to generate the PAL chroma signal—4433618.75 × 6 = 26601712.5
It's divided by 5 to generate the 2C07 pixel clock
It's divided by 16 to generate the 2A07 CPU clock
It's divided by 32 to generate the 2A07 APU clock.

In contrast, the 4.43MHz crystal in the metal box is just for decoding the PAL chroma signal, and it just needs to be the same as the 26.6MHz÷6 above.

If I remember correctly, the Hong Kong and Brazilian NESes start with clocks that are approximately 21.4MHz and divide that by 6 for their color remodulation (both from NTSC to some kind of PAL), rather than having a separate 3.6MHz crystal.

If you pick a different crystal frequency that's slightly off, you'll lose the color portion signal well before anything else breaks. Up to 1%, maybe 2% off should still be safely decoded as monochrome video. Further detuned won't be accepted as valid video, but audio should still work.
alfredocalza wrote:
Sat Jan 25, 2020 6:29 am
Forget abut it. I just checked and I only have 17 and 21 mhz crystals, but not 26 mhz ones.
Here's a schematic that will generate a 26.6MHz clock from a 17.7MHz crystal.
alfredocalza wrote:
Sat Jan 25, 2020 7:52 am
Now there are strange moving horizontal lines across the picture with different colours and cannot get the image back to what it was, even if I adjust the trimmer back in the same position as before. I think I might have broken the crystal or the trimmer!
More likely the trimmer. I'm curious about the "moving horizontal lines [...] with different colors", though.

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Re: Undesired Jail bars on French NES and checkerboard pattern

Post by Jarhmander » Sun Jan 26, 2020 8:21 am

lidnariq wrote:
Sat Jan 25, 2020 12:34 pm
What does the 26,06 mhz crystal on the nes motherboard do?
"Everything".
Image
((λ (x) (x x)) (λ (x) (x x)))

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