Mega Drive 1 - Not Working on my Samsung LCD
Since getting an LCD TV I found out that a lot of my retro gear wouldn't work with it. After a while I got an XRGB-2 to get around it, but I recently sold that and most of my consoles. I wanted to keep the MD though, but it wouldn't sync properly with it, resulting in a wobbly image, made even worse when switched to 60hz mode.
After looking at my RGB cable I realised I was using the Sync signal from the Composite Video signal, I rewired my RGB cable to use the pure Sync signal (pin 7 on the Din 8 socket). But I got no image. So I wired it back to Composite Video and made a short Scart Extension lead with a Sync Separator in it, nice idea, but it didn't fix it for my MD.
I stumbled across this the other day, so thought I would try it out, it works!! I love it and now the MD is left connected to our main TV all the time.
I've tried it on 2 consoles and got the same great results, all I used is a 220uF capacitor and a 75 ohm resistor.
There's some confusion with the video chip used in the MD - the CXA1145P, all the specs say that Leg10 is C-Sync In and Leg11 is C-Sync Out. When I played around with a continuity tester in my consoles both said that Leg10 was connected to Pin7 on the Din socket? That didn't make sense, and I had nothing to lose so thought I would experiment.
The first thing I did was re-wire my RGB cable so that Scart Pin 20 was connected to Pin 7 on the Din 8 plug (C-Sync, NOT Composite Video).
With the MD in pieces, and the heatsink removed you have access to the CXA1145P and the Din socket.
I forgot to photograph all of the process, IF I do another then I'll add some more photos. But for now here's some photo's showing my work.
I found Pin 7 on the Din 8 socket, found a trace leading to it, so cut that trace.
After checking Leg 11 on the CXA1145P chip, both sides of the motherboard I could see it wasn't connected to anything, so I picked up a 220uf 10v Capacitor (I think I had removed it from a SNES RGB cable at one point) and soldered the Positive Leg of the Capacitor to Leg 11 on the CXA1145P chip. (Most capacitors mark the Negative leg for you).
Then I picked up my 75ohm resistor and insulated it with heat shrink. I soldered one end to the Negative leg of the Capacitor, bent it into shape and soldered the other end onto the rear of the Din socket (pin 7)
I re-attached the heatsink and tested the console, it worked great, it's brilliant.
A BIG thank you to the posters (MKL and viletim) in the thread where I found the information.
UPDATE April 2011
Johan has emailed me to say that there's similarities to with
the PlayStation 1
Dear Mmmonkey,
like the megadrive 1, the older ps1 version sometimes has issues with the sync
on lcd tv's. Now the megadrives uses the
CXA1145P, the ps1 uses the CXA1645. Similar but a different pinout. Pin 5 on the
1645 is the com. video/sync. from there it's the same thing as with the
megadrive really. Just add a 220uF cap and 75R and lead it to pin 6 of
the multi AV. cut the old trace on pin 6 and presto.
