Famicom AV Mod Situation in 2019

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lidnariq
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Re: Famicom AV Mod Situation in 2019

Post by lidnariq » Tue Apr 09, 2019 8:50 pm

For whatever it's worth, the ferrite bead on my NES is 3.5mm diameter, 5mm long. Looking through through-hole ferrite beads (edit: ) of similar geometry available on DigiKey, I see they're all 10mΩ DC and in the range of 45-150Ω at 100MHz. (And when I measure its DC resistance, it's less than what my meters can measure). I'd really be surprised if it had any effect on anything below 7MHz, give or take - and all of this crosstalk is tremendously lower frequency.
Last edited by lidnariq on Tue Apr 09, 2019 11:29 pm, edited 1 time in total.

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Ultron
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Re: Famicom AV Mod Situation in 2019

Post by Ultron » Tue Apr 09, 2019 9:50 pm

lidnariq wrote:For whatever it's worth, the ferrite bead on my NES is 3.5mm diameter, 5mm long. Looking through through-hole ferrite beads available on DigiKey, I see they're all 10mΩ DC and in the range of 45-150Ω at 100MHz. (And when I measure its DC resistance, it's less than what my meters can measure). I'd really be surprised if it had any effect on anything below 7MHz, give or take - and all of this crosstalk is tremendously lower frequency.
Yeah, good point, I found one 30 ohms at 5MHz, but still, the crosstalk is lower than that.

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Ben Boldt
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Re: Famicom AV Mod Situation in 2019

Post by Ben Boldt » Tue Apr 09, 2019 10:43 pm

I actually did add an Amo-bead on the lead of the resistor connected to 5V. It had no visible effect when added in addition to the tantalum from 5V to GND. From what I understand, this is similar but different than a ferrite bead. They are definitely built different inside. We have these laying around everywhere, stuck in the cracks in the floor, etc, so I just grabbed one and threw it on to see what happened. Also, this is a very different location than you show in your circuit, Ultron.

I will try to locate the ferrite bead in my famicom, remove it, and measure it. We have a wonderful Wayne Kerr machine for measuring inductance and low resistance, perfect for this. At what frequency(s) would you guys be interested for me to measure this?

Also, quick unrelated question -- I am looking at setting up a 240p Test Suite cartridge, which requires the unusual BNROM mapper. I will need to make it out of an old NROM cart and 74HC161. Do you know how to hook up the '161? It must connect /ROMSEL and CPU R/W. I am thinking /ROMSEL goes to the clock input, and CPU R/W goes to /PE input?? Or is it the other way around? I can't tell from pictures of BNROM boards. Maybe I will just try it both ways and see what happens, but if anyone happens to know I would feel better about it.

lidnariq
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Re: Famicom AV Mod Situation in 2019

Post by lidnariq » Tue Apr 09, 2019 11:42 pm

Ultron wrote:but still, the crosstalk is lower than that.
I have to assume the ferrite there is to block a copy of the spurious emissions at some much higher frequency. Maybe at 3xcrystal = 64.4MHz ? It would be right in the middle of US NTSC channel 3.
Ben Boldt wrote:which requires the unusual BNROM mapper. I will need to make it out of an old NROM cart and 74HC161.
If you're starting with donors, any discrete logic mapper would be a suitable donor - UxROM, AxROM. Even MHROM/GNROM/CNROM if replacing CHR RAM is easier than adding a latch.
Do you know how to hook up the '161? It must connect /ROMSEL and CPU R/W. I am thinking /ROMSEL goes to the clock input, and CPU R/W goes to /PE input?
Yes. /ROMSEL goes to ↑clock so that at the end of the cycle it'll latch the value on the data bus. R/W won't have changed yet by that time.

tepples
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Re: Famicom AV Mod Situation in 2019

Post by tepples » Wed Apr 10, 2019 5:23 am

Ben Boldt wrote:We have a wonderful Wayne Kerr machine for measuring inductance and low resistance
If I didn't know better, I'd read "Wayne Kerr machine" and think "Batman and his arch-rival working together".
Ben Boldt wrote:Also, quick unrelated question -- I am looking at setting up a 240p Test Suite cartridge, which requires the unusual BNROM mapper.
240p Test Suite for NES comes in both UNROM and BNROM versions. UNROM can be built from incredibly common donors, but if you prefer the BNROM version, you can build BNROM out of an AN/AM/AOROM cartridge by cutting the 161's output corresponding to CPU D4 and running PA10 (vertical mirroring) in its place.

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Ben Boldt
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Re: Famicom AV Mod Situation in 2019

Post by Ben Boldt » Wed Apr 10, 2019 12:02 pm

tepples wrote:
Ben Boldt wrote:We have a wonderful Wayne Kerr machine for measuring inductance and low resistance
If I didn't know better, I'd read "Wayne Kerr machine" and think "Batman and his arch-rival working together".
LOL we call it the wanker.
Wayner Kerr.JPG
tepples wrote:
Ben Boldt wrote:Also, quick unrelated question -- I am looking at setting up a 240p Test Suite cartridge, which requires the unusual BNROM mapper.
240p Test Suite for NES comes in both UNROM and BNROM versions. UNROM can be built from incredibly common donors, but if you prefer the BNROM version, you can build BNROM out of an AN/AM/AOROM cartridge by cutting the 161's output corresponding to CPU D4 and running PA10 (vertical mirroring) in its place.
Oh, I didn't realize this, I will have to look into that. I have a damaged famicom "soccer" (NROM) that has been begging for something like this.
lidnariq wrote:
Ultron wrote:but still, the crosstalk is lower than that.
I have to assume the ferrite there is to block a copy of the spurious emissions at some much higher frequency. Maybe at 3xcrystal = 64.4MHz ? It would be right in the middle of US NTSC channel 3.
Will do.
lidnariq wrote:
Ben Boldt wrote:which requires the unusual BNROM mapper. I will need to make it out of an old NROM cart and 74HC161.
If you're starting with donors, any discrete logic mapper would be a suitable donor - UxROM, AxROM. Even MHROM/GNROM/CNROM if replacing CHR RAM is easier than adding a latch.
Do you know how to hook up the '161? It must connect /ROMSEL and CPU R/W. I am thinking /ROMSEL goes to the clock input, and CPU R/W goes to /PE input?
Yes. /ROMSEL goes to ↑clock so that at the end of the cycle it'll latch the value on the data bus. R/W won't have changed yet by that time.
I will check around and see what carts I have, otherwise I will go ahead with the '161 in the soccer cart.

I will probably take apart my NES and dig out the ferrite bead, I do not want to touch my beloved AV famicom unless necessary... We have a big snowstorm here, it might be until this weekend or Monday to test the bead.

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Ultron
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Re: Famicom AV Mod Situation in 2019

Post by Ultron » Wed Apr 10, 2019 5:58 pm

Ben Boldt wrote:I actually did add an Amo-bead on the lead of the resistor connected to 5V. It had no visible effect when added in addition to the tantalum from 5V to GND. From what I understand, this is similar but different than a ferrite bead. They are definitely built different inside. We have these laying around everywhere, stuck in the cracks in the floor, etc, so I just grabbed one and threw it on to see what happened. Also, this is a very different location than you show in your circuit, Ultron.

I will try to locate the ferrite bead in my famicom, remove it, and measure it. We have a wonderful Wayne Kerr machine for measuring inductance and low resistance, perfect for this. At what frequency(s) would you guys be interested for me to measure this?
If you can, check 1MHz, 5MHz, 10MHz, 100MHz. If it goes down to 100kHz, check that too. We can get somewhat of a plot that way. That's some nice equipment!!


I have time to test some things this weekend in regards to the jailbars. I plan on removing the NESRGB from my top loader and adding AV again, so this would be a good time to test.

lidnariq
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Re: Famicom AV Mod Situation in 2019

Post by lidnariq » Wed Apr 10, 2019 6:32 pm

Do we expect the reactance to change as a function of frequency? I thought ferrites were comparatively ideal in that regard...?

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Ultron
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Re: Famicom AV Mod Situation in 2019

Post by Ultron » Wed Apr 10, 2019 6:57 pm

lidnariq wrote:Do we expect the reactance to change as a function of frequency? I thought ferrites were comparatively ideal in that regard...?
Yes, reactance changes with frequency in ferrite beads. I don't expect the bead to be the solution, but it would be nice to know its characteristics. If Ben Boldt has the time and access the equipment, it would be helpful.
Ferrite Bead.png
X is the reactance in the plot.

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Ben Boldt
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Re: Famicom AV Mod Situation in 2019

Post by Ben Boldt » Wed Apr 10, 2019 7:18 pm

Ultron wrote:If Ben Boldt has the time and access the equipment, it would be helpful.
I can think of no better use of my time after work. :beer:

As I removed the ferrite bead from my USA NES, I noticed my big 2200uF cap was bulged! Glad we had a reason to go in there.

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Ben Boldt
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Re: Famicom AV Mod Situation in 2019

Post by Ben Boldt » Thu Apr 11, 2019 5:17 pm

I took apart my AV famicom and verified that the ferrite bead looks exactly the same as the one I removed from the NES, and also that my AV famicom matches exactly your schematic Ultron.

I dug into both of my NES's and found that they are quite different than the AV famicom, and actually each of them even had different circuits than each other in the RF box... Both of them had an additional NPN transistor, and also a 3.3uH inductor involved. I am thinking that this extra stuff was due to tapping the video signal into the RF modulator. But since the AV famicom has the best video quality of them all (at least in my experience), I am not thinking that the NES's more complicated circuits are going to take us in a good direction.

I plan to do these things and see the difference at each step:
  • change my resistor values to 300/110
  • add the ferrite bead (after measuring it of course)
  • add the 560pF cap
  • Maybe try throwing in a 3.3uH and see what happens

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Ultron
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Re: Famicom AV Mod Situation in 2019

Post by Ultron » Fri Apr 12, 2019 5:39 am

Ben Boldt wrote:I took apart my AV famicom and verified that the ferrite bead looks exactly the same as the one I removed from the NES, and also that my AV famicom matches exactly your schematic Ultron.

I dug into both of my NES's and found that they are quite different than the AV famicom, and actually each of them even had different circuits than each other in the RF box... Both of them had an additional NPN transistor, and also a 3.3uH inductor involved. I am thinking that this extra stuff was due to tapping the video signal into the RF modulator. But since the AV famicom has the best video quality of them all (at least in my experience), I am not thinking that the NES's more complicated circuits are going to take us in a good direction.

I plan to do these things and see the difference at each step:
  • change my resistor values to 300/110
  • add the ferrite bead (after measuring it of course)
  • add the 560pF cap
  • Maybe try throwing in a 3.3uH and see what happens
Yes, there were maybe 4 different RF boxes the NES used in its lifetime. Mitsumi made 2 of them I think (I have one with a Mitsumi). I did trace the circuit out for that one, just don't remember where I put it.

That's a good plan. I hope to do some testing this weekend too.

lidnariq
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Re: Famicom AV Mod Situation in 2019

Post by lidnariq » Fri Apr 12, 2019 11:36 am

https://console5.com/wiki/Nintendo_NES-001 claims there were six different RF modulators used on the front-loader; three by Mitsumi and three by Alps.

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Ben Boldt
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Re: Famicom AV Mod Situation in 2019

Post by Ben Boldt » Fri Apr 12, 2019 2:17 pm

I only know how to go up to 3 MHz with the Wayne Kerr. Here is the data:

Code: Select all

Freq (kHz) | L (nH) | R (mOhm)
-----------+--------+-----------
3000       | 845    | 1200
2760       | 830    | 800
2500       | 815    | 600
2000       | 790    | 350
1500       | 778    | 250
1000       | 771    | 199
750        | 780    | 155
500        | 791.5  | 62.5
250        | 798    | 20
100        | 790    | -8
64.5       | 781    | -6
10         | 760    | 2.5
1          | 750    | 2.5
0 (DC)     | n/a    | 1.75
inductance.png
inductance.png (10.05 KiB) Viewed 4575 times
resistance.png
resistance.png (9.92 KiB) Viewed 4575 times

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Ben Boldt
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Re: Famicom AV Mod Situation in 2019

Post by Ben Boldt » Fri Apr 12, 2019 3:48 pm

I played with this circuit some today, and I have some findings.

My circuit was actually pretty different than the AV famicom's circuit, it would not be apples-to-apples to change the resistor values. So I took everything apart and built the AV famicom circuit, skipping the ferrite bead and skipping the 560pF cap. I found that, without the tantalum from 5V to GND, this circuit starts out with much less jailbars, and the composite voltage is right bang on 1 Volt. Adding the tantalum still gives a big improvement though. (Scope shot shown with Tantalum)
tek00008.png
I then added the 560pF cap, and I found that it squashed the signal a bit, making it less than 1V, and also the colors became less vibrant and just in general more muddy. I felt that it was in no way an improvement to add this cap, unless perhaps it is meant for ESD protection.
tek00009.png
Next, I inserted the ferrite bead from my NES, the same one I tested above. I found absolutely no difference with or without this bead installed. Putting both the bead and the 560pF cap, was the same as just the 560pF cap and no bead. In no situation did I detect any difference from the bead. However, I am using good quality BNC cabling for all of this. Maybe crappier cables might benefit from the bead and 560pF cap, not sure.

I would say that the AV famicom, plus tantalum from 5V to GND, minus ferrite bead, minus 560pF cap is the simplest/best solution so far:

Code: Select all

                     (GND)
PPU.20 ----------------+---------------------------------+
 |                     |                                 |
 |                  | / (c)  2SA937                      +----O } Composite
 |         PPU.21 --|< PNP                                      }   Video
 |                  | ^ (e)      220uF                   +----O }
--- Magic              |     Electrolytic     110        |
--- Capacitor          +----------|(---------/\/\/-------+
 |                     |
 |   (+5V)     300     |
PPU.22 -------/\/\/----+

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