So a friend asked me to get rid of their SpongeBob TV. I had other plans for it…
- Safely open the TV
- Inspect the case and decide where to mount the input.
- Locate Jungle chip and on-screen display lines
- Mix the external RGB and internal OSD together.
- Absolutely no profit.
Are You Serious
As always, proceed at your own risk. Touching the wrong thing can literally kill you. Even SpongeBob. Respect and fear the TV.
After opening the TV (four philips screws and one torx center-pin security screw…yeah) I attached a thick gauge wire to a flat head screwdriver with some kapton tape, making sure to remove the rust for good electrical contact. I also removed the rust from the tip. I then wrapped the other end of the wire around the grounding strap of the TV and slid the tip of the screwdriver under the anode cap and touched the metal clip to discharge it. No pop or anything since this TV had been powered off for a long time, but this is an essential step nonetheless.
I carefully removed the neckboard, making sure to apply even pressure on all sides. There is a 1 pin cable from the ground strap that needs to be removed as well. The main board of the unit has a multi-pin cable going to the tube and a 2 pin cable for power, as well as a small 2 pin cable for the speaker that need to be removed.
The main board had notches on both sides so I had to pull out these tabs to remove the board.
Inspecting the Case
When I got the back of the case off, I looked at the back from the inside and lo and behold, a SCART hole.
Unfortunately, just behind this hole on the main board were a ton of components. Rather than mess with moving them, I opted to cut out the four remaining holes for a 3×2 RCA jack I had on hand and remove the original composite and mono audio jacks.
I then desoldered the existing RCA jacks.
I looked up the datasheet for the black chip on the right, which turned out to be the source of the OSD, not the destination. After some more research I found that the jungle chip was a square SMD chip on the bottom of the board, denoted by the diamond outline on the top of the board.
From these I was able to trace the RGB and blanking lines, where I removed the inline resistors.
I then used a schematic provided by Syntax on the shmups forum to replace the resistors with values that would allow me to mix in the RGB from the RCA jacks with the OSD signal without losing the OSD or requiring the use of a switch.
I replaced the existing blanking resistors with the values from the schematic, and then just put a wire from a 5V signal on the board to the non-ground leg of the grounding resistor.
I replaced the in-line OSD resistors. I then put one leg of 75 ohm resistors 2 ground and pointed them up out of the board, then put the inline resitors of the external signal into the other side of where the original grounding resistors were, mixing with the OSD, and then going through the existing 0.1μF caps into the jungle chip.
I twisted the 2 resistors for each signal on the top of the board together and joined them to some wires with shrink wrap that then ran to the back of the board.
I matched colors and connected the RGB to the RCA jacks. I then soldered the 1k stereo to mono resistors onto the back of the jacks.
I ran a 3 wire cable for audio, sync, and ground through the original RCA jack mounting hole to the underside of the board and attached them to video, video ground, and audio where the old jacks were soldered, then attached the jack with hot glue.
All that was left was to seal it up. I then tested it with some Super Mario World and to my absolute joy and relief, it worked.
I also recorded a short video of it working for the first time.
This was tons of fun and I am overjoyed that it worked out as well as it did. I’m not quite sure what I’ll do with this guy, but I’ll definitely have to check out some Spongebob games.
Syntax and MarkOZLAD from the shmups forum RGB TV modding thread.