After crudloads of nes and famicom modding I finally got back in the mood for some pc engine modding. This commission is another epic one for detroit44. For this job I'm rgb modding two pc engine duo r systems and then I'm building an external jamma adapter that you can plug these systems into so you can play them on an arcade cabinet.
These days using the ths7314 rgb amp for systems is all the rage so I built something similar to this schematic posted by the nice people from pcenginefx:
I used 3m ohm resistors to vcc instead of 3.6m ohm. I didn't bother with the 330 uf caps and between vcc and gnd I just used a 0.01 uf cap which I plan to switch with a 0.1 uf for some nice power decoupling.
I tapped rgb + composite sync from the appropriate pins of the huc6260 video chip which is the same video chip found in any model of the pc engine or turbografx 16 system. This chip is fantastic if you change a little circuitry you can also get 99% perfect s-video from it too.
The picture wouldn't sync up at all. After checking my work over and scratching my head for a while I realized that the pc engine rgb guides out there also have you amp sync as well as rgb. Unfortunately the ths7314 can only amp three signals so I needed to build something separate to clean up sync. I used the old 1992 transistor amp schematic for sync and it worked for a couple of seconds but then lost sync. I next ditched the amp and constructed myself a lm1881 circuit and....
This part took much longer and more hardware than I was expecting. But I'm glad it's over, the rest is all stuff I've more or less done before. This was the only part that was really treading a little bit into uncharted water.