A while ago (back in October, yikes) I posted how I had made a circuit that let you keep the OSD and replaced the big multi-pole switch with a simple on-off SPST. I apologize for taking this long, but since my hastily assembled test circuit worked and the PCB software I was using started irritating me, I sort of lost the motivation. I've recently switched to kicad and, finding it a much better tool, I've set out to finish the damn thing right. I'm still not done plotting out the PCB, but here's the schematic and how it works if anyone is still interested. Message me and I can send you the schematic itself, or the PCB file once I finish it. Eventually. I promise.
I used an LT1675
, a fast switching RGB multiplexer that's made for applications such as these. I wired the OSD RGB to the RGB 1 input pins (1,2 & 3) and the external console RGB to RGB 2 (6,7 &
. When the select pin is low, it'll output RGB2 and rapidly switch to RGB1 when select is high. The OSD blanking signal is used for this.
The OSD blanking is also connected in parallel to an or gate, SN74LVC1G32DBVR
, along with the RGB-on signal, 5V DC coming off a SPST switch. The output from the or gate is then sent out to the jungle IC's blanking pin. This makes it so that a) if the external RGB is off, the OSD blanking will switch to RGB1, the or gate will pass along the blanking signal and everything is as usual. b) if external RGB is on, OSD blanking can still switch to RGB1 but the output the jungle IC blanking pin is still the usual DC that blanks the whole screen.
Finally, the LT1675 requires negative voltage, for which I used an LM2776
. Perhaps some TVs may have a -5V rail you can use.
The schematic is for a simple JVC setup that has 0.7Vp-p video signals, 5ish V blanking and 75 Ω impedance, but it can be adapted to any TV that can be modded.
E: One more thing; the LM2776 datasheet states that the charge pump capacitor, C3 in the schematic above, needs
to physically be as close to its C+ and C- pins as possible. It's not kidding. At first I had it about a centimetre away and... 0V on the -5V output. Just a heads up.