The CXA2075 AV Famicom

Today I soldered together the video circuit of one of the kits I ordered. I wanted to test if it's possible to replace the cxa1645 that comes with the kit with a cxa2075 so I didn't solder in the encoder chip. Since I just wanted to test if the chips would be compatible I wired up the cxa2075 in such a way that it would easily be removable. So I present you with......

The cxa2075 av famicom prototype:



And does it work?



Better than I expected! Now I'm going to clean up my gaming area and test to see if the video quality looks improved over the cxa1645. There's also a chance that the picture quality will be even more improved with the encoder soldered right onto the kit but I ran out of loose cxa2075 chips and I'm waiting on the next batch to show up.

Did some testing and indeed the picture is sharper than before! Also I think the colour encoding looks a little better than before! I ordered some more loose cxa2075 encoder chips a while ago so I'll wait for those to show up before I solder one directly onto the kit pcb.

Nice work Drakon! I'll be ordering the chip to replace the 1645 in my kit. Was it a simple drop in replacement or did you have to change the circuit surrounding it a little?

teknix1 wrote:

Nice work Drakon! I'll be ordering the chip to replace the 1645 in my kit. Was it a simple drop in replacement or did you have to change the circuit surrounding it a little?

It's almost a drop in replacement. The composite video circuit is different and I havn't messed around with wiring that yet.

CXA1645:



CXA2075:

Nice work! Seems like there's a slight change in brightness or contrast. Regardless, I'm very anxious to see where you can get from here by playing with the circuit.

teknix1 wrote:

Nice work! Seems like there's a slight change in brightness or contrast. Regardless, I'm very anxious to see where you can get from here by playing with the circuit.

Yeah the 2075 kit I weakened the resistor because the s-video from these kits looks a bit dark. Really there's nothing to "play with" at this point it's as good as it will ever get right now.

This is awesome, any chance you might share the specifics of this mod? What value of resistor, etc... I got my board yesterday. Still waiting on the CXA2075, should be a matter of days now.

Thanks in advance!
Nic

teknix1 wrote:

This is awesome, any chance you might share the specifics of this mod? What value of resistor, etc... I got my board yesterday. Still waiting on the CXA2075, should be a matter of days now.

Thanks in advance!
Nic

Uhh I already have extra cxa2075 chips you didn't need to order any. Anyway the av famicom kits I use are designed for the cxa1645. The cxa2075 is meant to be a pin compatible drop in replacement for the cxa1645 which it is. I only changed one part from a cap to a resistor but even that part's only necessary for composite video. Anyway just check the datasheets for the cxa2075 and the 1645 and you'll see for yourself.

Sounds good, I'll take a peek at the datasheets then.

Thanks
Nic

After extensive testing this mod is a complete success and 100% finished. The only thing my cxa2075 video circuit lacks is composite video but I don't care at all about composite video so I consider this mod as completed.