Famicom AV Mod Situation in 2019

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Eicar
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Famicom AV Mod Situation in 2019

Post by Eicar » Tue Feb 19, 2019 2:01 am

Hi,

I've just gotten a Famicom that I would like to AV mod. This is the standard HVC-CPU-05 revision. However, I'm unsure about what mod to go for.
I've read through forums all the way back to 2009 and up today and there seem to be a wide range of possible solutions, all with their own pros and cons.
The goal for me is to have the cleanest composite signal without jail bars and interference. Mono audio (without buzz'ing) is ok, since I already have multiple other solutions to cover stereo (Like the NT Mini). I've also looked at premade kits like the ones sold here:

- Console5.com - https://console5.com/store/nes-toploade ... d-kit.html (Based on the original AV Famicom schematics?)
- Otakus-store - http://www.otakus-store.net/en/modding- ... cable.html (No idea what this design this is based on... Claim to be free from jail bars?)
- Retrofixes.com - https://store.retrofixes.com/products/o ... pgrade-kit (Single transistor mod with a few extra caps for audio filtering?)

All suggestions are welcome.

-Eicar

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Ben Boldt
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Re: Famicom AV Mod Situation in 2019

Post by Ben Boldt » Wed Feb 20, 2019 8:49 am

I also wonder about this. I have done 2 AV mods where I removed the PPU and wrapped it in copper tape, replaced caps, added extra bypass caps all over the place, used all thin coax wires, etc., and 1 of those famicoms still had very slight jailbars. I wasn't sure what else to try.

I have had GREAT experience with using a single 1/8" TRRS jack out the side of the famicom, then the appropriate AV cable. It is a very clean minimally-destructive way to get AV out of the famicom. Beware though that there are 2 slightly different lengths of TRRS and it does matter.

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Re: Famicom AV Mod Situation in 2019

Post by koitsu » Wed Feb 20, 2019 12:04 pm

Eicar wrote:All suggestions are welcome.
I suggest not modding your Famicom at all. Try an AVS instead.

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Re: Famicom AV Mod Situation in 2019

Post by rainwarrior » Wed Feb 20, 2019 3:10 pm

Ben Boldt wrote:I also wonder about this. I have done 2 AV mods where I removed the PPU and wrapped it in copper tape, replaced caps, added extra bypass caps all over the place, used all thin coax wires, etc., and 1 of those famicoms still had very slight jailbars. I wasn't sure what else to try.
I did a very simple mod and ended up with only very slight jailbars. ;)

For an example of how slight: here's a video.

I kinda feel like jailbars on a Famicom AV mod are mostly down to luck, some devices are just worse than others no matter what you do. I'm uncertain whether desoldering the PPU to apply copper tape is helpful enough to justify doing.

(Edit: I forgot to mention I also put a bypass capacitor across the PPU power source. It's a very non-invasive addition that I think is worth trying before considering taking the whole PPU out.)
Ben Boldt wrote:I have had GREAT experience with using a single 1/8" TRRS jack out the side of the famicom, then the appropriate AV cable. It is a very clean minimally-destructive way to get AV out of the famicom. Beware though that there are 2 slightly different lengths of TRRS and it does matter.
TRRS is an interesting way to connect. I just used 2 x RCA, myself.
Last edited by rainwarrior on Thu Feb 21, 2019 5:07 pm, edited 2 times in total.

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Re: Famicom AV Mod Situation in 2019

Post by Ben Boldt » Wed Feb 20, 2019 7:04 pm

rainwarrior wrote:The copper tape and the rest of that seems like superstition to me.
Shielding is sort of unpredictable and hit & miss, but it is a real thing. It makes more of a difference the higher frequency and longer lengths that you are dealing with. To your point, composite video across 5 inches of unshielded wire (~1 inch of which is inside the PPU chip) is probably on the threshold where it starts to matter.

One instance where I know that shielding made a huge difference was with my Sega Genesis SCART cable. The cable I bought was not shielded at all and it had pretty nasty jailbars and ghosts on the screen. I chopped off both ends, and also chopped both ends off of a VGA cable. I then soldered the SCART ends onto the VGA cable, and the difference was amazing. I hoard VGA cables from recycle bins ever since. It also slightly improved my SNES SCART experience when I did this.

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Re: Famicom AV Mod Situation in 2019

Post by rainwarrior » Wed Feb 20, 2019 8:39 pm

Sorry about the way I said that. Yes I didn't mean that shielding isn't a thing, I just don't think it really helps with the Famicom AV mod, from all the accounts I've heard over the years. Every account I'd heard of it was either that they ended up trying it but it didn't fix the jailbars, or they had done it anyway without trying something easier first so there was no comparison, and I'd also heard of several people (myself included) who don't have much of a jailbar problem without doing it.

Though, if you did try it both ways and found it made a noticeable difference, that would be good to know your experience. I haven't tried it myself ('cause I got jailbar-lucky), I'm just going by what others have said about it, and desoldering the PPU is a lot of work and risk of failure if it's not really going to help.
Last edited by rainwarrior on Thu Feb 21, 2019 5:08 pm, edited 1 time in total.

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Re: Famicom AV Mod Situation in 2019

Post by Eicar » Thu Feb 21, 2019 3:24 am

rainwarrior wrote: I did a very simple mod and ended up with only very slight jailbars. ;)

For an example of how slight: here's a video.

I kinda feel like jailbars on a Famicom AV mod are mostly down to luck, some devices are just worse than others no matter what you do. Desoldering the PPU to apply copper tape seems like superstition to me.

(Edit: I forgot to mention I also put a bypass capacitor across the PPU power source. It's a very non-invasive addition that I think is worth trying before considering taking the whole PPU out.)

TRRS is an interesting way to connect. I just used 2 x RCA, myself.
Thanks! I will probably start with the same schematics and take it from there. Btw, did you use the 2sa937 transistor or something else? Also, did you use an electrolytic capacitor, or a ceramic one for the PPU VCC/GND? Do you remember the capacity?

I'll post the result later. I'm still waiting for some parts in the mail :)

** Update: I Just found a pile of 2sa1015... They are also PNP transistors so I guess they can be used as a replacement for the 2sa937? **

-Eicar

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Re: Famicom AV Mod Situation in 2019

Post by rainwarrior » Thu Feb 21, 2019 1:56 pm

I used a 2N3906, which I believe is an extremely common part, but I don't know transistor part numbers intimately so I can't help suggest substitutes. Check the datasheets maybe.

I can't remember what capacitor I used, it was several years ago now. Might have actually been a large ceramic I had on hand, or possibly tantalum. I think I was avoiding electrolytic (personal paranoia?), but I assume polarized is fine for this application. Edit: Ben Boldt suggests that ceramic is the way to go, below.

Sorry, I'm not much help for the details. I didn't design the circuit I was just following a recipe (+ the bypass cap which just seemed like something worth trying). Maybe Ben Boldt or someone a bit more versed than me in this topic could comment about substitutions. All I have to offer is my own anecdote of one successful mod, and what I've heard reported by others.
Last edited by rainwarrior on Thu Feb 21, 2019 5:09 pm, edited 1 time in total.

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Re: Famicom AV Mod Situation in 2019

Post by Ben Boldt » Thu Feb 21, 2019 3:31 pm

I used to be a HUGE fan of tantalums but got scared of them lately. If they get reverse voltage at all, it can be doom for the cap. I think tantalum might not be the best choice here, they work their magic best on voltage rails and things that always stay positive. But these days, there are very good and cheaper alternatives to tantalum.

I am not sure about transistor substitutions for video signal. In the site I linked to, it had me remove a transistor and re-use it for this purpose, so that is what I did.

Bypass caps should be ceramic and small in value, recommend 10nF. Anything 1-100nF is OK. The purpose of the bypass cap is to "short out" high frequencies, which means low ESR at high frequency. That is what small ceramics do best. It might be tempting to put a big 100uF electrolytic for this purpose, but bigger isn't better. A big electrolytic won't have any effect at all at high frequency where you need it, really defeating the purpose. Bigger is not better in this case - use ceramic with short leads.

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Re: Famicom AV Mod Situation in 2019

Post by Eicar » Fri Feb 22, 2019 6:24 am

The 2sa1015 appears to be working just fine. I just made a temporary breadboard build just to test it and the image quality on my Sony PVM is actually very nice... I mean this is all looong cable lengths connected to a breadboard. I'm actually very surprised that it looks this good. @Ben: What you say about ceramic caps also makes a lot of sense. I've previously repaired jamma boards and those are usually filled with 104 caps (100nF) all over to filter noise. Those board are also very big and often two boards connected together so noise filtering is also very important. (If anyone is interested you can read more about my repair work on my blog-page: https://www.retrobits.no/).

However, back to my famicom. I do have jail bars. I've used SMB to test because it has a nice blue background. I'll probably get some time this weekend with my oscilloscope, so then hopefully I will be able to find the source of the problem.
I like to investigate problems first.. I don't do random things and hope for the best.. I've attached a few images if anyone is interested...

-Eicar
Attachments
smb.jpg
IMG_20190221_230509.jpg

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Re: Famicom AV Mod Situation in 2019

Post by Ultron » Tue Feb 26, 2019 8:17 pm

I was planning on testing this out too. I have a version 6 PB.

The copper shield can do some help. Also, putting the PPU in a high-quality socket may help too, since it increases the distance from the board traces, which is what the copper shield is protecting the PPU from.

The 2 systems that have AV built in (AV Fami, NES) have inductors in their video path. The NES has 2 - there is one extra in the RF/AV box, probably to help filter out noise picked up from the RF modulator components. The other one in the NES and the AV Famicom are ferrite beads.

The original Famicom does not have an inductor in the video path. I think the top-loader does (have to check again), but with the AV mod, it is bypassed.

I find it interesting that all these circuit leave it out, or say "not necessary". Who tested that they are not necessary? It would be interesting to see what the frequency is of the jailbars with the o-scope.

As far as the transistor to use, any jellybean PNP will work. It is being used as a buffer.

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Re: Famicom AV Mod Situation in 2019

Post by Eicar » Wed Feb 27, 2019 2:49 am

Hi again!

I've reached the end of round 1 when it comes to researching this. To sum it up, I've NOT been able to find the real source of the problem for the jailbars, however i have been able to remove ALL jailbars from the composite video signal. I would also like to mention that I almost have zero knowledge on analogue video signals. I've always lived my life on the digital side, so all this it pretty new to me. I'm just trying to learn as I go along. There's also no better way to learn something than to actually get your hands dirty. If I'm writing something here that's completely wrong, or incorrect then I would very much like to get some feedback. My main motivation here is to learn about analogue electronics and any help is appreciated.

So as someone mentioned earlier, small ceramic caps like 100nF between Vcc and Gnd will remove high frequency noise from the input. Most arcade jamma-boards are saturated with them. I tested multiple ceramic caps between the PPUs VCC and Gnd However, this does not have any impact on the jailbars at all. And to me it also makes sense. Jailbars must be caused by a repeating cycling interference to the signal as it has a very defined and visible footprint on the observed video signal. When I looked at the VCC on the board it struck me that the VCC looked "polluted" and also to some degree unstable. VCC would oscillate in the 4,7v-5,2v range depending on where I looked at the signal. The frequency was not clearly visible. My theory is that aging components on the board have started to drain more current over the years due to corrosion and leaking caps and that they are causing a voltage drop+interference to the VCC/Gnd planes. So, my next step then was to try to stabilize the VCC on the board. I first looked at the big 1000uF cap by the 7805 voltage regulator on the PSU. However, after removing and testing it I found that there was nothing wrong with it. It still had the 1000uF capacitance. Next, I tried to solder another 1000uF parallel to the first one, however that also didn't have any impact on the situation. Since I have the VCC and GND from the PPU out on my breadboard I then started to test different electrolytic capacitors to see if it had an impact on the jailbars. And it turned out it did! Starting with a 22uF it turned out to weaken the jailbars slightly. I then started to increase the capacitance and when I reached 100uF all the jailbars were completely gone. And I mean COMPLETELY gone! I also tried a 1000uF however, it didn't make it any better. After all it was more or less perfect already. The VCC looked better on my oscilloscope now as well. The oscillating variance was gone and there was only some brief noise/jitter left. I then played SMB for some time just to see how it looked. I noticed that sometimes like every 20-30 seconds I could see some white scanlines on random locations. If this is caused by ground noise going into the the EXT pins on PPU or if it's caused by noise on the VCC i don't know. However, when I applied a 100nF ceramic cap between the PPUs VCC and GND then the problem dissappeared. I played SMB for about one hour without any glitches so I'm quite happy with the result.

I also tried all the other "solutions" mentioned elsewhere with lifting the PPUs video pin. I actually went as far as removing the PPU completely using my vacuum de-soldering station. However, this did NOT have any impact on the jailbars at all. I also socketed the PPU, however I later reverted this at it would interfere with the eject button on the console. There's basically not enough room to socket the PPU. The grounded copper tape approach also didn't do anything at all so I never glued it on my PPU.

I also tried different video amp designs on my breadboard but I ended up with the amp design from Console5. This proved to give an excellent image on my PVM. It also has a simple high-pass filter on the output for removing the DC offset skew. Some designs also has a 560pF low-pass filter which I think will remove noise above 2,4Mhz or so. However, my video was already noise free so I didn't add it. I guess the my PVM and normal CRT TV already has some filtering builtin as well. (Isn't 2,4Mhz low-pass filter a bit too low anyway??)

I've added a few images here. However, the result looks better in real-life..

All feedback is appreciated!

-Eicar
Attachments
No more jailbars!!
No more jailbars!!
SMB on PVM
SMB on PVM
Final solution.
Final solution.
Board without PPU.
Board without PPU.
Removed PPU. Not needed......
Removed PPU. Not needed......

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Re: Famicom AV Mod Situation in 2019

Post by koitsu » Wed Feb 27, 2019 5:13 am

This is probably one of the most useful/detailed posts I've seen talking about solving the actual problem on an AV-modded Famicom. I actually appreciate it, even though I choose not to mod consoles (though I may make an exception for one particular system I have, keep reading).

I have lots of questions. I'll start with these. You said what fixed the jailbar problem for you was:

1. Adding a 100uF electrolytic capacitor...
1a. ...which is JWCO brand, and spec'd at 16V, as I could tell from the picture...
1b. Between what and what? It isn't clear exactly from your story, you just say you had PPU VCC and GND hooked up to a breadboard and then kinda "magic!"
1c. Since electrolytic caps are polar, what did you connect the positive and negative legs to?

2. Adding a 100nF ceramic disc capacitor between PPU VCC and GND...
2a. Is this the cap labelled 104 in your photo? (It's the only ceramic I see in the photo)
2b. What voltage?

3. What is the JWCO brand capacitor depicted in your photo on the far left of the board? Is it related to the jailbar problem? If not, ignore. If so:
3a. What is it wired/connected to?
3b. What are its specs?
3c. Since electrolytic caps are polar, what did you connect the positive and negative legs to?

More things, saving the best for last:

4. For your electrolytic cap(s) you used JWCO (Jiaweicheng Electronic Co. Ltd / 佳维诚电子有限公司) brand caps, from Shenzhen, Guangdong, China. I've used these caps myself with general success -- they're inexpensive, easy to get, and "get the job done" -- but the badcaps.net forum and eevblog forum both consider them to be "best-effort" and not long lasting. If you plan on keeping your modded Famicom in good condition, I'd suggest picking another cap brand (Rubycon, Nichicon, Panasonic, ELNA). They're quite a bit more expensive, but you can find them on eBay from reputable places (if you want eBay seller names within the US that are worthwhile, let me know, as I've bought from a couple and would be happy to give you links to them).

5. Did you have jailbar problems with the Famicom before you did your AV mod, or only after? I think this piece of information is crucial. We do know that the jailbar problem can plague both RF and non-RF Famicoms (I have an actual real/non-modded AV Famicom myself, but also have a top-loader NES (RF)).

Why I ask what I did about #5: now if only people could figure out how to solve this problem in this particular manner for the NES top-loader, which is mostly RF-only and notorious for having some of the worst jailbars you've ever seen. I own one (I bought it shortly after it came out, so roughly early 1994), yet it's always been this way. I don't want to hijack this thread for the NES top-loader -- we have several threads on that system/subject already, but all of them are pretty much "black magic" dust heaps of generally vague and not-very-helpful information. The only thing we do know for sure is that some SUPER rare top-loaders (very late-gen) actually had a completely redesigned circuit board (see pictures in linked thread; the right PCB is the redesigned one): one was still RF, the other used a multi-out jack similar to the real AV Famicom (not modded) and thus was composite, and both completely rectified the problem. The rare ones were supposedly only repaired models (back when you could send your products into Nintendo for repair + serviced + sent back to you), not actually sold-on-the-shelf models.

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Re: Famicom AV Mod Situation in 2019

Post by Eicar » Wed Feb 27, 2019 6:33 am

Hi,

That was alot of questions. I'll try my best to answer... :)

1. Yes! I put it between PPU VCC (pin 40) and GND (pin 20). Minus on CAP goes to GND like in a normal bypass cap setup.
1a. Yes, I ordered a huge pack from china with different values a while back. I'm guessing they're not the best electrolytic caps based on the price and they might dry out over the years. I can replace them again if needed. :)
1b. I soldered two wires from PPU pin 40 and pin 20 to my breadboard. It was then easy to hot-swap different bypass caps on the breadboard to see the results live.
1c. + goes to PPU pin 40 (VCC), and - to PPU pin 20 (GND)

2. Yes, between the same pins as above
2a. Yes, it's a normal 104 ceramic disc (100nF). You see it right under the PPU between pin 20 and 40. I used shrink plastic to cover the legs. I love shrink plastic :)
2b. I have no idea. These are no-name ones. Normally 104s should survive 50V.

3.
Ok, let's clear up a few things here. After I did the breadboard testing I also discovered that the location of the 100uF didn't matter that much. So instead of soldering it directly between pin 20 and 40 I ended up soldering it between VCC and GND on the left side of the PCB. This is still quite close to the PPU. Since there was a nice place further up to the right side of the board as well I also put a second 100uF there. This didn't have any impact on the image in anyway. You must remember that these bypass caps are only there for flattening the DC voltage on the board. However, electrolytic caps will not filter high frequency jitter. For that you need lower values ceramic disc capacitors (like the 0.1uF = 100nF). The discs should also be placed as close to the chips VCC/GND pins as posible to make it as efficient as possible. The larger electrolytics are just "buffers" that will stabilize the VCC across the pcb. I added two on the PCB. One would have worked just as fine. The red and black cable on the left side of the PCB (VCC+GND) goes to the actual video amp together with PPU video out pin 21.
(I ended up lifting the leg from the board since I had already taken it out. However, it didn't effect the jailbars if it was lifted or not. I tested both.) This circuit is "hidden" in the lower left part of the case. You can can see some resistors etc. there it you look closely. The final video out then goes along the joystick cable on the left side and all the way out the back. I also hooked up audio out from pin 46. I sent this through a 1kOhm resistor and a 22uF cap to remove any DC voltage from the output. This also works as a high-pass filter.

4. I'm not going to argue with you here. I'm well aware that these caps are probably not the best. I always measure the capacitance of the caps before I use them. If they are far from the labeled value then they go to the recycle bin. How long they will live I also don't know. If you have URLs to good quality electrolytic caps with good prices then by all means I would like to know.

5. I live in the PAL region of the world. Even though my PAL TV can deal with NTSC composite signals it's unable to tune in on Japanese RF frequencies. This also means that I have no idea if the jailbars are present on the RF part of the signal. I've only seen the composite signal via my own av amp. This is the circuit I used for my mod: https://console5.com/wiki/File:NES_Topl ... ematic.png

I will probably try to get hold of more famicoms. Even broken ones, just pcbs or the once in bad shape just to research this further. If you know anywhere I can buy old famicoms in bulk for a good price then please let me know. Buying one by one from ebay gets expensive quickly due to the shipping cost. If I could by 4-6 in one batch from somewhere it would be great! :)

I hope I was able to give you some satisfying answers.

-Eicar

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Re: Famicom AV Mod Situation in 2019

Post by tepples » Wed Feb 27, 2019 7:36 am

Is your TV "cable-ready" in the sense that it has a mode for various countries' analog cable band plans? If so, I've made another topic about receiving RF signals on a non-Japanese TV.

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