AV mod made "easy"? - updated, more questions

Started by SlumberingWeird, June 05, 2020, 10:26:40 am

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yes the buzzing is usually from the mic. Just cleane the graphite sliders on the joystick 2 PCB and with a very fine sandpaper about 2500 do the metal springy slider thing.
About the further improvements on the mod without cutting the pin 21 or trace from it to the the original transistor .
I read in some threads that you can add a 22mF inductor in series right before the center pin on the video RCA to reducing jail bars even more, but I did not tested this yet, because do not have the inductor with similar parameter  :) 


I did the mod on a HVC-CPU-07. I used a BC557B instead of 2N3906 (friend have already some of them...)
I'm quite happy with the output, I mean it's better than what I was expecting.
There is still more or less some jailbars depending on the color of the background, worst is probably SMB3, but it's not outstanding.
However, very top and bottom of picture is missing. Is there something I can do ? Any idea ?
I have only one CRT TV (trinitron) for testing, I never had such important issue with other devices. I assume TV settings are OK.


Check how to change the image geometry on your TV. You might need the remote to access the service menu. Some TV-sets actually has knobs for changing some things but this is mostly found on monitors and some very old TV-sets.

But if other devices are fine, it might be the AV-mod that is the culprit.
Does your other devices use the same signal as the Famicom? By that I mean NTSC composite. Some TV-sets may store different settings for different types of signals, meaning that even if the geometry is fine for PAL you may need to change it for NTSC (assuming your TV supports both PAL and NTSC).


TV supports both PAL/NTSC, SECAM also, but you are pointing something, I have no issue with NTSC, but it's not composite NTSC. Other devices are RGB.

This TV have a service menu with dozens of settings, including geometry and lots of things I don't understand, but as far as I remember, they don't look specifics to the input. I will check again.
Unfortunately, I don't have anymore another TV to try out. Also OSSC won't work with composite.


A seems like a very good TV, you may want to look up how to change geometry on the internet, there are probably youtube videos with similar settings as found on your TV. If you have some sort of flashcartridge solution for your Famicom (or about any other console) you can use the 240p Test Suite to generate a test picture that you can use to see what is considered overscan and what is action safe display area. You then adjust the picture until the overscan area is more or less just outside the screen. There is no one perfect setting, especially not for Famicom/NES as games very often shows more or less artifacts at the edges when scrolling, so you would have to keep that in mind. If you crop out too much overscan some games will have the status bar outside the screen. Edge garbage is a characteristic of the Famicom so some overscan is unavoidable.

Yeah if the TV supports that many different signals it only makes sense that it would store different geometry setting profiles for NTSC, PAL, SECAM, RGB 60 Hz, RGB 50 Hz etc.

"NTSC RGB" of course doesn't make sense since NTSC is a type of analog color encoding used in RF/composite/S-video (while RGB equals no color encoding), but I guess your TV may store different setting profiles for 60 Hz RGB signals and 50 Hz RGB signals, since a 50 Hz RGB video source probably uses PAL timing for hsync while a 60 Hz RGB video source uses NTSC timing for hsync. The different hsync timing would make the picture a bit too much to the left or right if they use the same settings, so it makes sense to store separate settings, I know my CRT does.


Thanks for the explanation, and the ideas !
I could find information that confirm TV supports NTSC4.43 and NTSC3.58

I don't have any flashcartridge for the famicom, but I can use my PC-Engine (RGB) as I see a 240p suite is available.
This is even better, I will see if settings for the famicom affect the PCE
I will try today or tomorrow...


problem solved
hum.... this was actually VERY stupid
this is 16/9 TV, so it has one feature to make 4/3 looks like 16/9 by cropping a little bit top/bottow and streching right/left
when input is RGB, it switches automatically to full 16/9
when input is composite, it does nothing and keep actual setting ... that's the reason why very top/bottow was missing

240p test shows also geometry is not perfect, and red tends to bleed on the left.
I will try service menu, but 25 years old caps might not help, and geometry/color has never been perfect even when it was new.

So finally, the mod works very fine, with limited failbars :)


If you have a scart on your TV you can force it to change the mode by one of the scart pins:
"Pin 8, the function switching pin, carries a low frequency (less than 50Hz) signal from the source that indicates the type of video present.

0V-2V means no signal, or internal bypass
4.5V-7V (nominal 6V) means a widescreen (16:9) signal
9.5V-12V (nominal 12V) means a normal (4:3) signal"
(Taken from: https://pinouts.ru/Audio-Video-Hardware/Scart.shtml )


yes, maybe useful to somebody.
I will keep as it is, I just have to remember to force to 4/3 ...
I used a TRRS jack, so no more space for additional wire.


Oh widescreen, it's truly a very good TV. Take good care of it.


Is it the audio and video are not already boosted/filtered? Why use additional components?


Quote from: FAMICOM_87 on March 06, 2023, 11:47:03 amI read in some threads that you can add a 22mF inductor in series right before the center pin on the video RCA to reducing jail bars even more


Have you a link to this thread ?
Looks something wrong, if it's an inductor, it should rather be mH
if it's a capacitor, 22mF is not an usual value...


December 08, 2023, 01:43:42 am #27 Last Edit: December 08, 2023, 01:50:20 am by FAMICOM_87
I do not remember from where I read that. And yes my bad, it is 22μH  (Microhenry) ! you can try with other values like 10 to 30 for example as well, and pick the best one for your taste :)

Edit here you are :