Famicom with AV Mod is not working

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

Moderator: Moderators

Mitchel
Posts: 11
Joined: Mon Feb 06, 2023 12:45 am

Famicom with AV Mod is not working

Post by Mitchel »

Hello,

I'm still new here in the forum, but have come across it several times during various searches. I hope this is the right subforum. I have purchased a Famicom, as well as two games and have a problem and hope you can help me. With the Famicom, I knew that I had to install an AV mod to connect it to my TV so that the console would work for me.

Now I have the problem that I only get a black picture (with a green tint I would say) displayed when I start the Famicom with and without a game.

Here I have made two pictures of my AV Mod modification. I used the board from CatHouse Games: https://www.cathousegames.com/nes-av-mod
1675674008906.jpg
1675674008890.jpg
I connected the three lines with a TRRS cable and from there via composite video to my TV. Now I get the following picture on the TV, no matter if I have a game plugged in or not. When the console is off, a blue screen is displayed, so something is being transmitted.
1675674008826.jpg
I have also output the PIN21 from the PPU to an oscilloscope and get this signal, again regardless of whether a game is plugged in or not.
1675674008858.jpg
1675674008842.jpg
I hope someone has experience and can find with me a solution to my problem.

Some more hints to my setup. I have the board revision HVC-CPU-GPM-02, operate it with a plug-in power supply (9V, 1A, inside minus, outside plus) and have exchanged all capacitors which are specified here for the board: https://wiki.console5.com/wiki/Famicom.

On my AV Mod board I get 4,93V at the +5V voltage, which I would see as ok for now.

Many greetings from northern Germany
Mitchel
darleiv
Posts: 69
Joined: Wed Feb 23, 2022 10:55 pm

Re: Famicom with AV Mod is not working

Post by darleiv »

eliminação de barras verticais em clones.jpg
lidnariq
Posts: 11429
Joined: Sun Apr 13, 2008 11:12 am

Re: Famicom with AV Mod is not working

Post by lidnariq »

Mitchel wrote: Mon Feb 06, 2023 4:19 am I have also output the PIN21 from the PPU to an oscilloscope and get this signal, again regardless of whether a game is plugged in or not.
1675674008858.jpg
1675674008842.jpg
That is a valid video signal. But do you see the same on the video output from your amplifier?

The gradient from black at top to green at bottom is suspicious, unless that's an artifact of your TV's viewing angle.
Mitchel
Posts: 11
Joined: Mon Feb 06, 2023 12:45 am

Re: Famicom with AV Mod is not working

Post by Mitchel »

lidnariq wrote: Mon Feb 06, 2023 11:37 am That is a valid video signal. But do you see the same on the video output from your amplifier?

The gradient from black at top to green at bottom is suspicious, unless that's an artifact of your TV's viewing angle.
Thank you for your answer. The output of the pcb is lower but shows the same signal.
IMG_20230206_210601.jpg
The gradient is not correct. I made a new picture in the dark. The complete screen has the same color.
IMG_20230206_205238.jpg
On the TV directly it is darker and not so green.
Joe
Posts: 649
Joined: Mon Apr 01, 2013 11:17 pm

Re: Famicom with AV Mod is not working

Post by Joe »

I don't know if the levels are correct, but it seems to work with your TV, and a solid colored screen is normal when there's no cartridge.

Have you tried cleaning the cartridge connector?
lidnariq
Posts: 11429
Joined: Sun Apr 13, 2008 11:12 am

Re: Famicom with AV Mod is not working

Post by lidnariq »

Do you hear video game sounds? Or does it just stay there?

A solid green screen means several parts are working, but also that several things aren't.

If you put your oscilloscope on CPU pin 4, does it continue to change when the screen is green? Or does it end up stopping either high/low some time after reset?
Mitchel
Posts: 11
Joined: Mon Feb 06, 2023 12:45 am

Re: Famicom with AV Mod is not working

Post by Mitchel »

Joe wrote: Mon Feb 06, 2023 1:45 pm I don't know if the levels are correct, but it seems to work with your TV, and a solid colored screen is normal when there's no cartridge.

Have you tried cleaning the cartridge connector?
Hi Joe,
Yes I cleaned the contacts of the module with isopropanol and also tried both games from two different sellers.

lidnariq wrote: Mon Feb 06, 2023 1:48 pm Do you hear video game sounds? Or does it just stay there?

A solid green screen means several parts are working, but also that several things aren't.

If you put your oscilloscope on CPU pin 4, does it continue to change when the screen is green? Or does it end up stopping either high/low some time after reset?
Hi lidnariq,
no I do not hear any sound. As soon as I turn on the console, this screen appears. This is as I said black-green, so not completely in light green.

When I measure the CPU pin 4 with the oscilloscope I get a straight line so just an offset. With the multimeter I measured 184mV.
I also pressed the reset button. The video signal (PPU PIN21) goes low when I hold it down, so it goes to GND. However, the CPU PIN4 remains unchanged at 184mV even when pressed and held.
1675674008890 - Kopie.jpg
Joe
Posts: 649
Joined: Mon Apr 01, 2013 11:17 pm

Re: Famicom with AV Mod is not working

Post by Joe »

Mitchel wrote: Mon Feb 06, 2023 11:05 pmHowever, the CPU PIN4 remains unchanged at 184mV even when pressed and held.
Does it do anything when you let go of reset?

If it doesn't do anything, how about pin 3 or pin 29?
Mitchel
Posts: 11
Joined: Mon Feb 06, 2023 12:45 am

Re: Famicom with AV Mod is not working

Post by Mitchel »

Joe wrote: Mon Feb 06, 2023 11:31 pm Does it do anything when you let go of reset?

If it doesn't do anything, how about pin 3 or pin 29?
No, I see no difference after releasing the Reset Button.

When I measure Pin3 I have a voltage of 190mV. When I Press the Reset Button it goes Low to 0V. When I release it, it goes directly to 190mV again.

At Pin 29 I get a nice frequency of 20 MHz as you can see in the picture below.
IMG_20230207_160947.jpg
lidnariq
Posts: 11429
Joined: Sun Apr 13, 2008 11:12 am

Re: Famicom with AV Mod is not working

Post by lidnariq »

CPU pin 3 must rise to 3V (or higher) before your Famicom can do anything. Check if you accidentally shorted it to pin 2 or anywhere else.
Mitchel
Posts: 11
Joined: Mon Feb 06, 2023 12:45 am

Re: Famicom with AV Mod is not working

Post by Mitchel »

lidnariq wrote: Tue Feb 07, 2023 11:00 am CPU pin 3 must rise to 3V (or higher) before your Famicom can do anything. Check if you accidentally shorted it to pin 2 or anywhere else.
Thank you for the hint. I check and also desolder audio from Pin 2 and it is not shortened to this Pin3. It is still 190mV. Are there any schematics that I can check, where this Error can be?
lidnariq
Posts: 11429
Joined: Sun Apr 13, 2008 11:12 am

Re: Famicom with AV Mod is not working

Post by lidnariq »

The leaked official Famicom schematic is here: https://www.nesdev.org/Ntd_8bit.jpg

As far as I can tell, pin 3 should connect to a capaicitor and the reset switch and nothing else.
Mitchel
Posts: 11
Joined: Mon Feb 06, 2023 12:45 am

Re: Famicom with AV Mod is not working

Post by Mitchel »

lidnariq wrote: Tue Feb 07, 2023 1:49 pm The leaked official Famicom schematic is here: https://www.nesdev.org/Ntd_8bit.jpg

As far as I can tell, pin 3 should connect to a capaicitor and the reset switch and nothing else.
Thank you very much for the information. I have desoldered the AV Mod, the capacitor and also the reset button. In addition, I looked again directly at the reset pin and can not find a short there. Furthermore, I still only have a voltage of about 190mV at the reset pin. Would you know what else I could test?
lidnariq
Posts: 11429
Joined: Sun Apr 13, 2008 11:12 am

Re: Famicom with AV Mod is not working

Post by lidnariq »

You could try adding a temporary external pullup resistor to pin 3.
Mitchel
Posts: 11
Joined: Mon Feb 06, 2023 12:45 am

Re: Famicom with AV Mod is not working

Post by Mitchel »

lidnariq wrote: Tue Feb 07, 2023 11:45 pm You could try adding a temporary external pullup resistor to pin 3.
What could I use there? 10k to +5V?
Post Reply