Text waterfall ahead! watch out!-
246A is a non-cost-reduced 246B/C
the ram expansion is 32MB, but there's 16MB onboard as well, 1 free slot, and what appears to be a slot similar to the 256's IO slot.
All of this is on the namco board.
The PS2 board is COH-H30000, an older version of the one we see in MOST 246B's. this IS the one we saw in a YJ auction as a 246B with a small heatsink (I'm going to refer to it as 246B1 in technical discussion until we have more info, but otherwise should be considered a B):
An interesting difference is that the power is supplied via a power socket on the top of the main board, NOT the push-through connection as seen in the GH-006 design.
I have a feeling that the 246B1 also uses a different namco board than a normal 246B as well, as the power is quite obviously seen being supplied via cable, not pin-through.
The sony board is actually a stack of 2 boards- I haven't been unable to separate them yet (can't get to the clip)- the interconnect is power-pin push-through like before, and the top board is very small- perhaps a regulator of some sort- I'll investigate later.
As usual the sony board is missing the digital video encoder.
The jamma interface AND the JVS interface operate independently and socket directly into the namco board. there is a power cable distribution system still.
the JVS IO has a 6-pin power plug on it (but only 5V is connected)- this is not used to power the system, but rather, by use of an external loopback, provide the JVS pcb with the 5V it needs to operate from the JAMMA interface.
the proper power plug on the JVS side of things is a 4-pin version of the same plug used on 246B-256... the wiring is: 12v, 5v, Gnd, Gnd- as such, it's easy to shift the 5v pin on the minimal cables I made between the 12 and Gnd, to get the system powered.
If the jamma board is connected to the JVS board by way of that external cable, shadowing appears- DON'T DO THIS.
Compatibility-
The 246A ships with a Teac CD-ROM drive. This drive will boot Bloody Roar 3, and presumably Vampire Night, RRV, and Wangan Midnight.
Putting in a DVD-ROM that works on a 246B+ will allow other games to work fine as well.
31khz works fine (with the same DIP configuration as seen on all other versions)
Basically, all 246A/B1/B/C have the same compatibility. the only differences appear to be in drive support.
Potentially, a 246A could be configured with a LOT more memory onboard by use of the ram expansion, but it's unlikely any game was ever made or tested to use this configuration.
The unused expansion board IO is unique to the 246, but it's possible that this platform was used for prototyping 256games/hardware- or some of the features of the 256 may have at least been in mind during its design.
Vampire Night-
The Vampire Night chassis is IDENTICAL in every way with the exception that the JAMMA IO board is not present. in its place is a metal filler plate.
IO for Vampire Night is handled via an external interface board as seen on the schematics in the manual (Listed as USB, BUT shows connection to the JVS port)
Bloody Roar 3-
Bloody Roar 3 is NOT drive dependent, but, like Tekken 4, is picky.
The LG DVD-ROM when used in the 246A will allow it to boot, and either the LG DVD-ROM or the Teac CD-ROM in the 246B will let it boot.
A non-compatible drive (Tekken 4 non-boot) appears to hang at the message:
[ SETUP CD LOCATION FILE ]
On a good boot, this message is followed by debug info about the copying of files to memory.
Interestingly, regardless of drive used on a 256, the game boots to this same message, then hangs.
ERGO:
System 256 is more than likely 100% compatible with all 246 games in theory. BUT, if the games use an ATAPI-specific command set, the will not boot, and instead hang right after the dongle completes its primary boot and prepares for disc access.
I feel that on this basis, tranfer of media to HDD/Flash Card would be possible, but the same games would retain incompatibility.
Bloody Roar 3 is 15khz only, but does support PS2 AND PS1 controllers.
I'm going to need to retest SC2 and see if it supports PS1 controllers as well.. My tekken 4 stick was instantly recognized and functional in BR3 at least, and this was very PRE-PS2.
EDIT:
One more thing-
Anyone else have a Bloody Roar 3 chassis- anyone?
Mine has some rework done to the Jamma pcb to connect Button 5 to the traces for Button 4. I'm curious if this came from Namco, Hudson, or some previous operator.