I googled for it on aliexpress and I see it is quite expensive (75$). In one of the phonos, seller shows (probably) his workshop where he assembles them. No idea if this is one-person masterpiece or some larger quantity production.
My first impression was really good:
* The design consists of two thick (1.5mm) PCBs connected together with two rows of header pins,
* There are no blobs, just discrete chips - RP2A03G CPU + RP2C02G-0 PPU. All other chips have their markings removed with sandpaper
* Bottom and top shell is made out of plexiglass, while borders are done out of some kind of plastic, everything is assembled using screws (only a little bit of hot glue for the batteries and speaker, which are permanently glued)
* Video quality was quite acceptable,
However, after powering it up, I found some oddities:
* Small speaker generates constant noise added to the sound (even if game does not play any music). Using head-phones makes it a little better.
* There is also some weird echo or reverb,
* There are minor graphic problems in some games (no, it's not the connector fault).
So I spent quite a lot of time trying to reverse-engineer it and found a lot of oddities:
** BOTTOM PCB **
1. Those two 16850 rechargeable batteries that power up everything are connected in parallel. No idea if this is good for their life-time or charging
2. Clock generation circuit is extremely weird which results in 0-3V amplitude clock and both CPU's and PPU's clock are driven by the same signal
3. Audio voltage drop and mixing resistors have non-standard values
4. There is a DB9 pin port (which can be used to connect external joypad for player 2). Its pinout is:
So except the standard signals needed for joypad, they added 4017.D1 and 4016.D1 (for connecting P3 and P4 famicom-like adapter). There are even 4017.D3 and 4017.D4 for zapper, but they routed and shorted both of the signals to the metal chasis of the DB port (LOL). OUT1 and OUT2 are not available so no external keyboard.
5. Instead of using 2*74x368 like in regular Famicom, they prefered 74x125+74x04
and some octal inverting buffer
It seems to be 74540
6. PPU-A13, present in the cartridge connector is not directly routed to PPU'a A13. Insted, they used some logic to make it appear like:
Code: Select all
PPU-A13 PPU/WE PPU/RD | PPU-A13 on cartridge connector 1 x x 1 0 0 x 0 0 x 0 0 0 1 1 1
Maybe this is source of those weird graphical glitches that appear in some cartridges (with slower EPROMS?)
7. Tiny DC power jacks looks quite fragile to me
8. The four LEDs connected as some kind of battery power indicator (?) have no resistors in series, causing extra bright light. This is the only chip in the bottom PCB that I have no idea what is responsible for (battery charging or discharge protection?)
** TOP PCB**
This is harder - I don't understand function of most of the chips. There is for sure 4021 for the built-in joypad, LCD controller and its eprommm, but there are a lot of other unknown chips (audio amplifier, something that generates turbo for butons, something that reacts for volume up/down)
* I checked the TURBO signal and it is 13.7Hz square wave. There are no signs of other non-square signals so it appears to be generated directly from the chip.
* I checked IC2 pins 15 and 16 when pressing VOLUME UP/DOWN buttons and they appar to be some clock/data signal generated by the IC2 into IC6 (there are 21 volume levels)
It makes me think that IC2 is some microprocessor for aggregating diferent functions. I haven't found any with that pinout (16 pin, 8=GND, 6=VCC, maybe it is CY8C4014SXI?)
* IC6 seems to be digitally controlled two channel potentiometer (FM62429)
* IC5 seems to be sound effect generator. The connections is very similar to the "echo" circuit in PT2399 (or HT8970)
* IC3 seems to be 4066 (four analog switches)
* IC7 is still unkown, but is is some kind of AUDIO amplifier (haven't found any with 8 pins, 6=VCC, 1/7=GND)
Surprisingly, there are no single electrolytic capacitor in the whole device. I soldered two and noise seems to be lower but it is still audible at some volumes, maybe the potentiometer adds it.
What the microcontroler does (except volume control) is not clear.
Its inputs are:
* sound generated by game,
* VOLUME UP/DOWN buttons
Its outputs are:
* DATA/CLOCK to the potentiometer,
* drive the POWER LED (but is still seems to be ON after power-up),
* drive voltage to the LCD controler via Q1 mosfet (but it stil sems to be ON)
* control those four analog switches (but it seems to turn on IC3A and IC3D and off IC3B and IC3C, resulting in the external audio/video mini jack to be efectively disconnected)
So either there need to be some special sound pattern or button combination to activate the AV jack.