Twin Famicom
Introduction
A Japanese exclusive variation of the Famicom, the Twin Famicom by Sharp (licensed by Nintendo) was released in 1986 and is unique in that it is a Famicom console with integrated Famicom Disk System (FDS). To learn more about the FDS please see Nintendo Famicom Disk System.
Rather than just a curiosity nowadays, however, anyone looking to get an FDS and Famicom separately will likely find difficulty getting hold of the required RAM adapter cartridge so having the disk system built-in to the Twin Famicom provides everything needed to experience the disk based Famicom games. Another bonus of having a Twin Famicom is that it has composite video output whereas the original Famicom had RF only.
Overview
There were two main models of the Twin Famicom, model AN-500R which is red with black highlights and complementary model AN-500B which is black with red highlights. In 1987 two additional models became available with turbo controllers and two new colour schemes; model AN-505-BK black with green highlights and AN-505-RD red with beige highlights. This page will focus on model AN-500R as that is what I own, however, a lot of the information will be applicable to the other models too.
The Twin Famicom originally came with a linear 'brick' power supply, model AN-500, rated for AC 100V 50/60Hz 21VA input and DC 7.6V 1.25A centre positive and has a barrel plug connector that plugs into the Twin Famicom. If you do intend to use the original power supply then you will need to use a step-down converter if your mains is rated above 100V or you can use an alternative suitably rated power supply that matches the original power supply output power requirements and polarity but rated for your mains voltage.
Not surprisingly since the Twin Famicom combines a Famicom and disk system that the Twin Famicom is much larger, measuring approximately 275mm x 250mm x 75mm. On the top of the console we find 'SHARP' and 'TWIN FAMICOM AN-500R' written near the cartridge port as well as some Japanese text which is possibly a warning or instruction for operating the system. Near the cartridge port there is a large sliding mode select switch which when pushed toward the cartridge port selects disk mode and if no disk has been inserted you will see a 'Nintendo/PLEASE SET DISK CARD' screen where Mario and Luigi run along the bottom of the screen, hitting the Nintendo sign to make it change colour. You can view a video of the animation below:
Curiously, when playing the animation in disk mode some Twin Famicoms display 'FAMICOM' instead of 'Nintendo' but others display 'Nintendo' even for the same model number. It's possible that early Twin Famicoms used the same BIOS as used in the original, standalone disk system You can see the 'FAMICOM' version of the animation here:
You can then insert a Famicom disk game and it will load but note that you will not be able to insert a cartridge until you change back to cartridge mode.
When the mode select switch is in the opposite position the console is in cartridge mode and a cartridge can be inserted (which you should do while the power is off). In front of the mode select switch is a push button for ejecting a cartridge that has been inserted (while the power is off).
At the front of the console is the floppy disk slot with a yellow disk eject button, a small red disk access LED, a large round grey reset button, and a locking beige power button at the far right. On the right side of the console are two expansion connectors, labelled A and B, with connector B hiding behind a sliding cover. Port A is an expansion connector just as you would find on an original Famicom for connecting 3D glasses, keyboard, etc., and port B is supposedly for connecting an FDS RAM adapter cartridge so that the Twin Famicom can function as a disk system for an original Famicom but I've found conflicting information online. Note that port B is very similar to the A/V port Nintendo would later use on its consoles, such as the SNES, and it's possible to modify an A/V cable to fit the socket.
At the back we have two cables for the two wired in controllers, an 8-pin DIN A/V connector (for an RF adapter which was included when the console was bought originally), a yellow RCA composite video connector, a white RCA mono audio connector and lastly the power connector. On the bottom of the console is a black trapdoor which when removed reveals expansion connectors C and D which are normally fitted with a kind of loopback cable. It appears that port C carries the internal RAM adapter signals and port D the drive signals so the cable routes those signals so the Twin Famicom functions as normal. It is unknown exactly what ports C and D were actually intended for in terms of expansion, outside of normal operating conditions.
On the underside of the console is a sticker with the model number AN-500R along with the power rating and serial number.
As mentioned, the Twin Famicom's two controllers are wired to the console as with the original Famicom but unlike with the Famicom which has space to hold the controllers either side of the console the Twin Famicom has space for the controllers at the back of the console. The controllers are a different design to those found on the original Famicom in terms of being branded 'twin Famicom', the colour scheme, and labelling the controllers as '1' and '2' respectively instead of 'I' and 'II'. The buttons on the controllers, however, are the same on the Twin Famicom as the original Famicom, as well as the player 2 controller having a microphone and microphone volume slider as with the original Famicom.
Games
The Twin Famicom is compatible with all Famicom cartridge and disk system games. To learn more about the disk games please see:
Internals
This section will deal with the Twin Famicom model AN-500R, however, the information will also apply to the other models.
To take apart the Twin Famicom you will need to remove 7 long screws from the underside and then the top can be separated from the other half, revealing the internals, which you can see in this photo:
In the top left we have a Mitsumi disk drive, which is very similar to the disk drive found in the standalone disk system for the Famicom and should be interchangeable. To the right of the disk drive is the A/V and power supply board, and toward the bottom is the main board including the cartridge port, expansion connectors and switches as well as the disk access LED. Of further interest on the main board are a couple of test points (TP101, TP102 and TP103) and the following ICs:
RP2C33A Famicom Disk ASIC containing a disk controller, sound synthesizer and 8KB BIOS ROM.
RP2A03E CPU.
RP2C02 PPU (under the heat sink which you can just about see poking out near the CPU to the right of the cartridge port.
6116ASP 2KB SRAM x2. Work RAM/Video RAM.
HM6264P 1KB SRAM. Unknown use.
HM48416AP-15 x4 16K x 4 bits. Makes up the 32KB part of the integrated RAM adapter used for disk caching.
As well as some glue logic type chips.
If you are opening the console for servicing it would be a good opportunity to look at the general condition of the PCBs to see if there are any leaking capacitors that need replacing. It is also a good idea to check the disk drive belt and to do that you will need to first take out the 4 screws holding the disk drive in place (there are only three screws holding down the disk drive in the photo above so it seems someone attempted a repair and lost a screw). Next you can turn over the disk drive and remove another 3 screws which are holding the back metal plate on. Once that plate is off you should be able to see whether the belt is still in one piece but if not the the remaining pieces of the belt will need to be removed before a new belt can be installed. In the following photos you can see that when I opened up my Twin Famicom the disk drive belt had broke (and there were pieces laying around inside the console).
Please see the Troubleshooting section on this page for more information about changing the drive belt.
Troubleshooting
A/V issues
The Twin Famicom outputs an NTSC-J video signal so if you get no output while the console is on make sure your TV/monitor supports NTSC. If the Twin Famicom is in disk mode it should show the 'PLEASE SET DISK CARD' screen. If you get a grey screen with a cartridge inserted while in cartridge mode then the cartridge may be dirty and need cleaning or it could be the Twin Famicom's cartridge connector that needs cleaning.
If you are able to play games but the graphics are glitchy then possibly the video RAM and/or PPU is bad and needs replacing. Please see this video for help:
Disk read errors
As with many old disk drives the drive belt usually goes bad with age, either becoming stretched or breaking into multiple pieces, so if you have trouble loading a disk game it could be time to change the belt. Please use a high quality replacement belt rather than just an elastic band as that will degrade over time and possibly break. As for obtaining a replacement belt you may find for sale online or if you have belt spares from other devices try to find one that matches the following spec which was taken from this site:
http://forums.nesdev.com/viewtopic.php?t=614
2mm (0.080 inch) to 4mm wide (0.160 inch), 1mm thick (0.040 inch), 229mm (9 inch) to 232mm (9.125 inch) inside diameter.
The following video goes over changing the drive belt and also deals with audio problems:
Here is another video on changing the drive belt which is for the standalone disk drive but should still be helpful for the Twin Famicom:
Disk Write Errors
It's possible that the copy protection of the Twin Famicom can cause write errors as the system sees the disk as invalid if there are no other issues with the disk drive (such as a dirty read/write head). Please see this site for information about disabling the copy protection, which should only be used as a last resort if you still get write errors after carrying out realignment:
All content of this and related pages is copyright (c) James S. 2021