I have an old Japanese MegaDrive 1 with one of those awful CXA1145 video encoder chips. Using RGB I get some ugly "jailbars" in all the blue colors.
Notice how the red and green colors look perfect.
The stock CXA1145 is wired up roughly like this:
And when I swapped the green and blue in and outputs like this:
- The blue colors were perfect but now the greens had jailbars. So the video encoder is definitely to blame here...
I also have another JAP MegaDrive 1 and the problem is the same on that as well. Tapping the R,G and B lines from the input of the chip doesn't work.
I read that the Sony CXA1645 is better so I ordered one and it got here yesterday. I removed the old CXA1145 from the MegaDrive and soldered it in like this:
Pin: Soldered to:
1 (GND): MegaDrive MB Pin 1 (GND)
2 (R in): MegaDrive MB Pin 2 (R in)
3 (G in): MegaDrive MB Pin 3 (G in)
4 (B in): MegaDrive MB Pin 4 (B in)
5 (N/C): Nothing
6 (SCIN IN): GND (not sure about this one...)
7 (PAL/NTSC): MegaDrive MB Pin 7*1
8 (N/C): Nothing
9 (YCLPC): 0.1uF > GND
10 (SYNC IN): MegaDrive MB Pin 10 (SYNC)
11 (N/C): Nothing
12 (Vcc): MegaDrive MB Pin 12 (Vcc)
13 (IREF): MegaDrive MB Pin 13 (?)*2
14 (VREF): MegaDrive MB Pin 14 (?)
15 (Y OUT): MegaDrive MB Pin 15*3
16 (C OUT): MegaDrive MB Pin 16*4
17 (N/C): Nothing
18 (FO): 20K > GND
19 (Vcc2): MegaDrive MB Pin 19 (Vcc)
20 (CVIDEO): MegaDrive MB Pin 20 (CVIDEO)
21 (B OUT): MegaDrive MB Pin 21 (B OUT)
22 (G OUT): MegaDrive MB Pin 22 (G OUT)
23 (R OUT): MegaDrive MB Pin 23 (R OUT)
24 (GND2): MegaDrive MB Pin 24 (GND)
Here are datasheets for both 1145 and 1645:
A picture of both in NTSC mode:
But it doesn't work :( I don't get any sound or video at all :( I have checked for shorts but all seems okay.
I then tried the following things according to the datasheets as I noticed several differences:
Pin 7*1 The PAL/NTSC line on the MegaDrive was neither GND or 5V which was very strange as this pin is the same on the stock video encoder and the machine is NTSC. I cut this trace and connected it to 5V.
Pin 13*2 I noticed the caps and resistors on the 1145 datasheet didn't match the ones in the 1645. I cut the trace to the pin and soldered a 47K and a 0.1uF (UNPOLARIZED, does that matter?) from pin 13 to GND.
Pin 15*3 I noticed that there were several differences after the Y OUT in the two datasheets. Since I don't need S-Video I decided to cut this pin.
Pin 16*4 Same as above. I cut the C OUT pin.
The MegaDrive still doesn't work :( There are a number of pins that still doesn't match 100% to the data sheet. Those are pins 12, 13 (unpolarized 0.1uF where the datasheet says polarized), 14 and 19.
I'm thinking that cutting ALL traces to the video encoder and soldering everything according to the datasheet might help. But really I'm more confused about pin 6 (SCIN). According to the datasheet this can be either GND or something else...:
I have no idea what the "SG4 SIN 0.5Vp-p" is so I just hooked it up to GND. Can this be why it's not working?
Any help would be greatly appreciated. I only need RGB video out if that makes it any easier.
I'm a bit worried why I don't get any sound when I hook it up as is. I mean the MegaDrive should work even with a faulty Video encoder, right?
I found this thread while searching for a solution yesterday:
It seems Retro has some experience on the CXA1645 chip so I hope you can help me here :)