Last month or so I've gone and done component mods to two more of these China TV chassis, and I've learned a bit more, and want to share that. I also re-visited one of my earlier mods.
I took these photos over a period of roughly a month, a little while ago (Jan/Feb). I've had to pick out the best, as the TVs have mostly been closed up and put away already, and don't want to open them up again just for photos. So I'll be using pics from three very similar, but different, China TV chassis in this post. You will notice some minor differences.
These next two TVs have the same basic China TV layout, same jungle. However, unlike the ones I did earlier, these PCBs don't have any blank spots for the extra resistors and capacitors. There are no convenient landing points for the component inputs, and there are no copper traces leading to the jungle pins [Pb, Y, Pr] -> [19, 20, 21]. There isn't even any copper trace around the Y input (pin 20)! It is what it is.
Means some fiddly soldering right onto the legs. Will need to scratch off copper trace connecting pins 19 and 21 (Pb and Pr). In this pic we can see that the trace connects 19 to 21, and then to C804, a 103 (10nF) ceramic capacitor. This 103 cap clamps the Pb, Pr signal pins to ground, to prevent unused inputs from "floating ". It needs to be removed. The first pic below is untouched and shows which pins are the signal pins; the second pic (from an identical but different TV) has had the trace scraped off between Pr and Pb, and C804 has been removed.
Before soldering, I did some crimping and put it all together into 4-pin female headers, which I'll explain in a moment.
For my first attempt at soldering to the jungles pins, I attached some stout leads to the wires to make them sturdier, then stuck the ends into the PCB holes for the pins, and soldered. This works OK, great even, but the wires shoot straight up and, though it is sturdier than it looks, I still worry it might break off accidentally. Not that this has ever happened. It works fine, I won't redo it, but I can do better!
See that 103 capacitor, C804, circled in yellow? It is the one I mentioned earlier - I forgot to remove it before taking the pics! I went back, removed C804, moved the Pr input to the newly vacated hole. I then also cleaned it all up, it is still quite messy in these photos, and sometimes you don't realise how messy something is until you see the high-res images. The black spots near the pins are just magic marker, so I know which pins to solder.
For the second TV, I took a different approach. I recycled some surplus 3-wire TV ribbon cable and added an extra wire for GND.
Then I stripped a few mm of wire, carefully laid the ribbon down on top of the jungle, bent the exposed wires to meet the pins, and secured it with some paper tape. The ribbon cable/wire has the right combination of being somewhat stiff yet flexible enough to make this work. This made the soldering much easier, and the wires more secure.
I put some coloured heat shrink on the wires so I wouldn't get them mixed up.
To make things more manageable, I created a mini input-PCBs for the input circuit. I used some offcut breadboard, 2 x 4-pin male connectors for IN/OUT, 3x100R resistors, 3x75R resistors, and 3x104 (100nF) ceramic capacitors. I've included a simple schematic. The last pic shows the input-PCB inside some heat shrink for electrical insulation. I cut some holes for the connectors. I didn't bother with heating the heat-shrink as it works perfectly the way it is, I can still remove it to get at the PCB inside, and those white connectors are a bit sensitive to heat.
104 (0.1uF/100nF) capacitors are pretty much always what you'll need for Pb, Pr. I've also gone with 104 (100nF) on Y, and that is right for these TVs. For other TVs with different jungles, some might go up to 1uF on Y, but I suggest starting with 100nF anyway. This is because capacitors in parallel ADD capacitance, and it would be easy to solder a 1uF capacitor below the 100nF. This would give you a total of 1.1uF, close enough for testing. If it works better that way for your TV, then you can make it permanent. If this seems confusing, then just stick with 100nF.
These input-PCBs are very convenient, especially now I have several TVs with the same component mod. In normal use, when the TV is closed, it is connected to the external side-input so standard video cables can be used.
When a TV is on my bench, for testing with GreenAntz connected, I can just unplug that external side input and use a shorter, more convenient cable that I've hacked. This saves space and hassle, the soldered connection to the jungle is more secure, and it is easier to work on the main PCB with everything unplugged.
I even created an input-PCB for one of my earlier mods, but without the input resistors/capacitors, as these are already present on the main PCB (see pics below). I just find it very convenient to use, and having all my TVs modded the same way makes it interchangeable.
For the connectors, I bought one of these kits with a range of JTC 2.54mm pitch terminal connectors with a range of sizes. The kits cost about $3-4 each and come with all the pins for crimping. I've been using a lot of 4P connectors, I tried to find these cheaper separately but could not. So I just bought another kit! I should probably invest in a better crimping tool too.
I will post again soon on:
- minor modification to the neckboard for a sharper picture
- schematics
- accessing and tweaking the service menu
- improving the picture sharpness
- hacking the EEPROM
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