Missing inputs on C2

[bodgit]

I have a C2 board that I've realised some of the player 1 inputs aren't working; namely the right direction and button 2. I've buzzed through from what I think are the correct fingers on the JAMMA edge to the pins on the 315-5296 I/O chip; both signals just pass through FLT34 or 38 and then both go through DA1, DA2 and RA4. Here's a diagram annotated with what I figured out:

Once I hit the I/O chip I was a bit stumped, and figured if that's the problem then I'm screwed. However on a hunch I tested the RA4 resistor array and the values are all over the place. Here's a closeup of RA4:

It's marked 102 so I'm assuming that's a 1KΩ array but I barely measure 650Ω on most of the resistors. Most importantly though, the two resistors I traced through I measure 12Ω and 90Ω (there's one other resistor in the array that measures 170Ω but I'm not sure what input that belongs to, nothing else appeared faulty on the input test in the service menu). The common pin on the array is tied to the +5V rail so I'm assuming this is being used for pullups.

Would this array being faulty be the likely cause of the two missing inputs? If someone could check my workings out, that would be appreciated!

 

[Apocalypse]

Hi,

From my experience it's almost always the 315-5296 custom chip (failing internally with a low resistance on input pins), but it's quite easy to pull the resistor array and check, who knows?
The good news is that custom chip seems easy enough to reproduce using latches and buffers.

 

[MoppelTheWhale]

if somebody ever make a repro of this - i would need one as well...

 

[Apocalypse]

@MoppelTheWhale I actually had a quick look and I'm pretty sure I can come whith a solution, when I'll have time...

 

[MoppelTheWhale]

You're the man! thanks!

 

[bodgit]

From my experience it's almost always the 315-5296 custom chip (failing internally with a low resistance on input pins), but it's quite easy to pull the resistor array and check, who knows?
The good news is that custom chip seems easy enough to reproduce using latches and buffers.

I pulled the resistor array and every resistor now measures close to 1KΩ so it does look like it's the I/O chip at fault. Guess I'm also interested in a repro then unless I can find a replacement.

 

[Catzoo]

I have the very same issue, and got to the same diagnostic after removing the RA, so i'm really interested in any solution that might help.

While i was working on this, i've had the idea of swapping the input physically to working one (with a custom jamma edge connector) in combination with a romhack that could swap input.

Is it even possible ? I don't have the skill to do such rom modification, but i wonder if it's possible, since the games are decrypted and checksum routines are well known ?

 

[GC8TECH]

This might help..... https://w.atwiki.jp/arcadegames/pages/40.html

 

[TulioAdriano]

I have a System C board that came with such an issue. Most likely a Jamma connector got plugged reversed sending 12V flying into some inputs. The solution was to replace the 315-5296 chip. Finding the chip wasn't hard. There are some posting on ebay for "Unknown SEGA IO board" that has 2 of those chips on it. Hot air desoldering took them out, then the hardest part was just to resolder it since it has a very fine pitch and many pins to attach, but once I got it done, the input issue was fixed.

 

[Catzoo]

Good job ! If you sell the 2nd one, shoot me a dm

 

[leadedsolder]

I think I've also got this problem on a Columns II (although not all the inputs are stuck – just right for one player, and left for the other,) and I have a couple loose System 24 mainboards that will probably also have this flaw, if it's that widespread. I noticed that this Japanese enthusiast has rebuilt what sounds like the decode and the latch(es) for the Port A/B controller inputs on some protoboard. I wonder how they kept it from fighting the original chip. Maybe it doesn't matter if the original chip is basically pulldowns now.

https://twitter.com/takarano_su/status/1276525433903648770

Would love a reproduction if it could be fit into the tiny QFP100 footprint, maybe a small pcb with castellated pins if such a thing is feasible. I will do some reading and see if I can figure out an equivalent circuit to stick on top and bodge in like this one.. CN4 would work on its own and be really clean, except that $840001, etc need A18 and A23.

 

[jacklick]

I was just troubleshooting a Columns stuck ON p1b1/p2b1 issue. Two Diode Arrays had a small hole in them and tested bad. P1 & P2 Button 3 were both reading dead short (even with all diodes and resistors removed). Interestingly enough, Button 1 didn't read shorted on input side but was being read that way. I concluded, like others here, jamma connector was flipped and 12v went to the button3 line blowing out the 315-5296 I/O chip. Anyway, good thread so figured I would post.