Famicom AV Mod Situation in 2019

Discuss hardware-related topics, such as development cartridges, CopyNES, PowerPak, EPROMs, or whatever.

Moderator: Moderators

Great Hierophant
Posts: 780
Joined: Tue Nov 23, 2004 9:35 pm

Re: Famicom AV Mod Situation in 2019

Post by Great Hierophant »

I did my own jailbar removal mod, but I feel like I did not do something quite right. My Famicom is an HVC-CPU-07 with a rev. E PPU and CPU. I used this board from CatHouse Games https://console5.com/store/nes-toploade ... d-kit.html because it replicated almost all of the "ideal" NESDev/AV Famicom circuit. I had also replaced the Famicom's RF/Power Board with a BackOffice Power VAMP v3 board to compare its composite output with the CatHouse Games circuit. The BackOffice Power VAMP v3 provides essentially the equivalent of the Twin Famicom's circuit.

In this photo you can see what I have done :
IMG_20210613_121431447.jpg

The tantalum cap used is 10uF/35V. The video amplifier transistor by the PPU has been removed. I could have but did not add the 560pF cap to the CatHouse Games board.

Here is a sample of jailbars after the mod :
Screenshot 2021-06-13 11-22-17.png
Here is a screenshot of the output of the Power VAMP v3 board vs. CatHouse Games board :

Power VAMP v3 :
Screenshot 2021-06-12 22-04-57.png

CatHouse Games :
Screenshot 2021-06-13 03-24-47.png
Any suggestions on how to improve the jailbars further?
User avatar
Ben Boldt
Posts: 1149
Joined: Tue Mar 22, 2016 8:27 pm
Location: Minnesota, USA

Re: Famicom AV Mod Situation in 2019

Post by Ben Boldt »

One thing I notice is that you have a rather long wire between the PPU and the cathouse board. As an experiment, you might try removing the cathouse board and using 3 very short wires directly to the PPU pins, and connecting the 5V/GND wires directly to the tantalum capacitor. Not sure it will help, but worth a try.
Great Hierophant
Posts: 780
Joined: Tue Nov 23, 2004 9:35 pm

Re: Famicom AV Mod Situation in 2019

Post by Great Hierophant »

I was unsure whether there would be any difference between a long cable before the amplifier or after the amplifier. I figured that the video signal has to travel that distance at some point. I will move the CatHouse games board as close to the CPU as possible and see if there is any improvement.
Great Hierophant
Posts: 780
Joined: Tue Nov 23, 2004 9:35 pm

Re: Famicom AV Mod Situation in 2019

Post by Great Hierophant »

Ben Boldt wrote: Sun Jun 13, 2021 11:46 am One thing I notice is that you have a rather long wire between the PPU and the cathouse board. As an experiment, you might try removing the cathouse board and using 3 very short wires directly to the PPU pins, and connecting the 5V/GND wires directly to the tantalum capacitor. Not sure it will help, but worth a try.
I think this is what you had in mind, or something close to it, but it didn't have any obvious affect on the jailbars :
IMG_20210613_200416834_HDR.jpg
User avatar
Ben Boldt
Posts: 1149
Joined: Tue Mar 22, 2016 8:27 pm
Location: Minnesota, USA

Re: Famicom AV Mod Situation in 2019

Post by Ben Boldt »

Sorry it didn't help but worth a try I guess. I had not intended for you to move your tantalum but apparently it didn't make a difference. What value is your tantalum (uF)? My experiments showed that it should be in the range 4.7uF to 47uF, and not larger or smaller than that range.
User avatar
Ultron
Posts: 24
Joined: Tue Feb 26, 2019 6:36 pm

Re: Famicom AV Mod Situation in 2019

Post by Ultron »

I would try connecting the Tantalum cap between pin 20 and pin 40 on the PPU. Though I don't think this will fix it, it's worth a try.
Great Hierophant
Posts: 780
Joined: Tue Nov 23, 2004 9:35 pm

Re: Famicom AV Mod Situation in 2019

Post by Great Hierophant »

Ben Boldt wrote: Sun Jun 13, 2021 8:16 pm Sorry it didn't help but worth a try I guess. I had not intended for you to move your tantalum but apparently it didn't make a difference. What value is your tantalum (uF)? My experiments showed that it should be in the range 4.7uF to 47uF, and not larger or smaller than that range.
10uF is the value. I recall someone saying that the specific value is not critical so long as it is in that range. I think I had to move the tantalum because when I attached the +5v and GND wires to the legs of the tantalum as it was connected directly to the pins, the system wouldn't start. Why I don't know, but if the +5v and GND wires were attached to the voltage and ground planes, or the PPU pins, or as shown in the photograph, then there would be no issue.
Ultron wrote: Sun Jun 13, 2021 8:43 pm I would try connecting the Tantalum cap between pin 20 and pin 40 on the PPU. Though I don't think this will fix it, it's worth a try.
I might try that, although I might need to extend the legs of the tantalum a bit, I don't have any axial tantalums which would be ideal for the purpose.
User avatar
Ben Boldt
Posts: 1149
Joined: Tue Mar 22, 2016 8:27 pm
Location: Minnesota, USA

Re: Famicom AV Mod Situation in 2019

Post by Ben Boldt »

Glad to hear you have 10uF, that's perfect. Do you have more? You can try putting more than 1 in parallel, and additionally to pin 40.

The tantalum cap was basically the only thing we found that gave any improvement to the jailbars. It is definitely worth tweaking with it. Pin 20 to pin 22 (the way you had it before Great Hierophant) seemed the best and most convenient on my Famicom but please do experiment and let us know anything that shows an improvement. It should have been OK to connect the wires to the legs of the tantalum; you may have had a short or bad connection.

When you change things, it's tricky to tell if it is getting better by looking at the screen. It has to change a lot to tell a difference. It helps touching additional caps here and there with it running. You can watch the screen and see if you notice changes as you connect and disconnect the cap repeatedly. This will be the only way to identify things that cause slight improvements.
Great Hierophant
Posts: 780
Joined: Tue Nov 23, 2004 9:35 pm

Re: Famicom AV Mod Situation in 2019

Post by Great Hierophant »

Ben Boldt wrote: Sun Jun 13, 2021 9:10 pm Glad to hear you have 10uF, that's perfect. Do you have more? You can try putting more than 1 in parallel, and additionally to pin 40.

The tantalum cap was basically the only thing we found that gave any improvement to the jailbars. It is definitely worth tweaking with it. Pin 20 to pin 22 (the way you had it before Great Hierophant) seemed the best and most convenient on my Famicom but please do experiment and let us know anything that shows an improvement. It should have been OK to connect the wires to the legs of the tantalum; you may have had a short or bad connection.

When you change things, it's tricky to tell if it is getting better by looking at the screen. It has to change a lot to tell a difference. It helps touching additional caps here and there with it running. You can watch the screen and see if you notice changes as you connect and disconnect the cap repeatedly. This will be the only way to identify things that cause slight improvements.
I can salvage another 10uF tantalum from one of my IBM PC video cards, as IBM loved to use tantalums in the early days. I posted a few Youtube videos showing the mod's video output so far :

https://youtu.be/xPgF8CFkY-Q - Unmodded Famicom RF
https://youtu.be/QSRcSyCgorg - Famicom with Power VAMP board
https://youtu.be/qXz1wV_OrBc - Famicom with CatHouse Games board
User avatar
Ben Boldt
Posts: 1149
Joined: Tue Mar 22, 2016 8:27 pm
Location: Minnesota, USA

Re: Famicom AV Mod Situation in 2019

Post by Ben Boldt »

Great Hierophant wrote: Mon Jun 14, 2021 8:46 am I can salvage another 10uF tantalum from one of my IBM PC video cards, as IBM loved to use tantalums in the early days.
That breaks my heart to something like that die for this. You should sell the video card on eBay and use the money to buy brand new tantalums.
Great Hierophant
Posts: 780
Joined: Tue Nov 23, 2004 9:35 pm

Re: Famicom AV Mod Situation in 2019

Post by Great Hierophant »

Ben Boldt wrote: Mon Jun 14, 2021 4:09 pm
Great Hierophant wrote: Mon Jun 14, 2021 8:46 am I can salvage another 10uF tantalum from one of my IBM PC video cards, as IBM loved to use tantalums in the early days.
That breaks my heart to something like that die for this. You should sell the video card on eBay and use the money to buy brand new tantalums.
I tried it and it made no difference, so it went back to its card. Then I removed the single tantalum and that made no perceptible difference either in the jailbars either. The jailbars have this fluctuating pattern on a non-moving screen when the jailbars are more or less prominent over time. It cycles every 4-5 seconds.

I really think this rev. E PPU chip is pretty much a noisy beast which nothing will help, like some/many of the 2C03 chips.
User avatar
Ultron
Posts: 24
Joined: Tue Feb 26, 2019 6:36 pm

Re: Famicom AV Mod Situation in 2019

Post by Ultron »

Tantalum or Electrolytic caps in that size are a dime a dozen. I wouldn't salvage them from old equipment, try a new one.

Again, I know a fix for some is not a fix for all. This really needs a permanent solution for all. I was experimenting with a fix back in the day, but it's been a while since I looked at it. I'll have to check this out again, hopefully this week.
Great Hierophant
Posts: 780
Joined: Tue Nov 23, 2004 9:35 pm

Re: Famicom AV Mod Situation in 2019

Post by Great Hierophant »

In a perfect world I imagine a cheaper NESRGB like FPGA board which only generates composite video and s-video but does it in the way the PPU originally did it or could have done it and replaces the Power Board so the Eject functionality of the Famicom is not lost. No custom palettes, no dejitter, just clean reconstructed PPU video.
User avatar
Ben Boldt
Posts: 1149
Joined: Tue Mar 22, 2016 8:27 pm
Location: Minnesota, USA

Re: Famicom AV Mod Situation in 2019

Post by Ben Boldt »

Great Hierophant wrote: Tue Jun 15, 2021 11:36 pm In a perfect world I imagine a cheaper NESRGB like FPGA board which only generates composite video and s-video but does it in the way the PPU originally did it or could have done it and replaces the Power Board so the Eject functionality of the Famicom is not lost. No custom palettes, no dejitter, just clean reconstructed PPU video.
I think an ideal RGB / HDMI mod should replace the entire PPU and add VTxx functionality.
Post Reply