Wonder Boy (Original, Sega 834-5191-01 PCB) factory jumper wire mod?

petsematary125

New member
Joined
Jun 23, 2015
Messages
8
Reaction score
1
Location
Plano, Texas
I recently got my Wonder Boy PCB mostly working (it crashes at random, but I think this is due to corroded sockets which I plan to clean or replace), but I am unsure of where exactly this green wire is supposed to be soldered.
One end is connected to the Sega 315-5012 chip on pin 6, the other is seemingly supposed to be connected to a pin on IC51, an M74LS257AP. However, the 74LS end of the wire was detached, so I am not sure which pin it is supposed to be connected to. I believe this is a factory installed wire since I see some other boards which have the exact same mod, the problem is I can't clearly discern which pin it is supposed to be soldered to.
As best I can tell from another boardest that I can find online, it appears to be pin 1, but again, I can't tell for sure.
The board seems to run with it attached to pin 1, though I don't know if an incorrect connection could be a possible cause of the random crashes.

Any help would be appreciated, as it seems like it is a bit difficult to find clear photos of this PCB model running Wonder Boy.
 

Attachments

  • Wonderboypcb.jpg
    Wonderboypcb.jpg
    904.3 KB · Views: 16
Last edited:
You can use the Up n Down schematics for this, here.

It looks like the 257s are involved in the DIPs but have some Data lines and a AD0 line at pin 1.

IMG_4403.jpeg

The custom IC110 has the AD0 linked to its pin 2

IMG_4404.jpeg

Not sure if this helps but that's what I can tell from the schematics…

p
 
Last edited:
Thanks for the info. Based on the schematic I'm still not entirely sure what exactly the wire mod would impact, but there is an Up n Down PCB on ebay which has the same wire connected to pin 1 on that 74LS257, so unless I hear otherwise, I'll probably just leave it connected there.
 
Thanks for the info. Based on the schematic I'm still not entirely sure what exactly the wire mod would impact, but there is an Up n Down PCB on ebay which has the same wire connected to pin 1 on that 74LS257, so unless I hear otherwise, I'll probably just leave it connected there.
You can at least test to see if pin 1 of either 257 is connected to the custom IC110 pin 2 on your pcb...

p
 
No continuity between pin 1 on either 257 to pin 2 on IC110/315-5012. There is continuity between Pin 1 on both 257s and pin 6 on IC110/315-5012 (pin 1 on IC51, the 257 next to Dip Switch A, is what is connected directly to pin 6 on IC110 with the wire)
 
Pin 6 is A4...

According to the MAME source, one set of DIPs reads at 0x0c (IORD), and the other set reads at 0x0d or 0x10, depending on the game.

0x0d would want A0 to the 257s -- 0x10 would want A4 -- but the SW5 decoding to pin 15 might have to change as well, and this screen is too small to search through the schematics to see where that's generated.

Code:
/* I/O map for systems with an 8255 PPI */
void system1_state::system1_ppi_io_map(address_map &map)
{
    map.global_mask(0x1f);
    map(0x00, 0x00).mirror(0x03).portr("P1");
    map(0x04, 0x04).mirror(0x03).portr("P2");
    map(0x08, 0x08).mirror(0x03).portr("SYSTEM");
    map(0x0c, 0x0c).mirror(0x02).portr("SWA");    /* DIP2 */
    map(0x0d, 0x0d).mirror(0x02).portr("SWB");    /* DIP1 some games read it from here... */
    map(0x10, 0x10).mirror(0x03).portr("SWB");    /* DIP1 ... and some others from here but there are games which check BOTH! */
    map(0x14, 0x17).rw(m_ppi8255, FUNC(i8255_device::read), FUNC(i8255_device::write));
}
 
Back
Top Bottom