nfg.forums

So, I'm not sure if anyone can help me, but this is really baffling me.  I'm doing a Saturn 3-region single switch mod using that I saw from mameworld and mmmonkey.co.uk.

So the US region is the default position (switch is set in the middle or "off"), and each ends of the switch is either JP or UK.  So we have the jumper settings at:

Region - JP6(GND)/JP7(+5v) - JP10(+5v)/JP11(GND) - JP12(+5v)/JP13(GND)
----------------------------------------------------------------------------------------
JP - JP7(+5v) - JP11 (GND) - JP13(GND)
US - JP6(GND) - JP10(+5v) - JP13(GND)
UK - JP6(GND) - JP10(+5v) - JP12(+5v)

Now, my problem is that JP region is okay, but both the "off" position and the other "on" position of the switch is UK.  That is, I end up with a JP-UK-UK setting.

But according to the circuit diagram from mameworld,


I don't quite understand how I can even possibly get the above result.  US-UK is only changed by sending +5v or GND to JP12/13.  Right now going from "off" (US) to UK position does nothing, since my saturn recognizes them both as UK - meaning it's JP12/13 is staying on +5v.

Yet, when I switch over to JP, it works okay, but how can that be?  The above diagram doesn't do anything to JP12/13 when going from US to JP.  I'm soooo confused.  

Any Saturn and/or electronic wizkids know where I should start looking?  I'm not an electronics expert by any means, so any tip would be appreciated.

So whip out your multimeter find out what's really going on...

BTW, you should use a CMOS inverter chip (74HC04, 4049, etc), not TTL (7404, 74LS04, etc).