Component modding CRT TV

[Zebidee]

This thread is to document component-modding CRT TVs. Thought I'd kick it off with a "China TV" that I bought new a few years ago.

Here it is, new and sealed in the box. Well, it is mostly new - the CRT tube is actually recycled/refurbed. But the rest of the TV, including chassis and shell, is completely new. The brand/model is "Distar CTV1121-20" and it is assembled in Thailand.

I'm going to put up a few posts with pics to break up the text, so please be patient with me. To start with, here is the TV I'm going to be component modding today:




 

[Zebidee]

Here are some pics of the TV inputs for the Distar CTV1121-20. The only options are RF and AV/composite.

There are 2 AV inputs, at the back and the side (the second set of AV connections at the back are for output). Both back and side AV inputs are the same, the TV doesn't differentiate them internally.

I'm going to repurpose the side AV inputs into component/YPbPr inputs, so that is why we have a close-up.


 


Also here are some pics to show that the TV works. You can see the normal menu via remote control. I've already accessed the service mode and enabled "YUV" there.

 


I'm not going to get into how to access the service/factory mode here. This is covered in the attached the service/factory adjustments manual for a TV very close to this one (not identical, but in English and close enough that it works).

[Zebidee]

OK, enough of the introductions. Now for some nitty-gritty.

I pulled the back off the TV and removed the chassis for closer inspection.

The area circled in yellow is where we will be focusing our efforts (below).





As an aside - this chassis, in various forms, seems to be officially called the "China TV" chassis (thus the CTV prefix), and it is very common especially in Asia and especially in developing countries. So in addition to China this includes India, Philipines, Indonesia, Malaysia, Vietnam, Thailand... and that is just what I've seen so far, so probably many more. Anyway, back to the modding.

First thing to look for is the jungle chip. On this TV it is the big one in the middle. In general, when looking for the jungle chip on any TV look for the big one first.

In this case the jungle IC designation is "8895CSNG7GG9". This chip incorporates OSD (On Screen Display) functions. There are no RGB inputs and no OSD RGB inputs to hijack (as they are all internal to the chip).

A close inspection of the schematic reveals component inputs (labelled "Cb", "Y", "Cr" at pins 19,20,21).





Now for a spoiler alert - this TV chassis is built onto a PCB that already has component input capability, but the manufacturers decided to leave all that out to save some money. Fortunately for us, we can use that to our advantage.

Following the PCB traces back from those jungle component input pins brings us to the part of the board we will be working on. The pins connect through to the 3 x ceramic disc capacitors (103, 0.01uF, C801, C802, C803). These 103 capacitors simply clamp these unused component inputs to ground, best practice is to not let them "float".





For the next step, we are going to remove the 103 capacitors (C801, C802, C803), and we are also going to remove the 6 wire bridges (R804-R809) you can see above them


NEXT - Action

[Zebidee]

OK, now for the action you have been waiting for.

Let's start by removing some stuff - those 3 x 103 ceramic capacitors (C801-C803) and 6 wire bridges (R804-R809), as framed in yellow below.




Here is what it looks like once they are gone. I've added some blobs of colour for tracking signal paths

 


Next step is to replace the 103 caps with 2 x 104 for C801 & C802, which correspond with Pr & Pb. I'm going to use a 1uF electrolytic cap for C803 (Y). After some tests and looking at other schematics, I decided to go with a 104 (0.1uF) ceramic capacitor on Y as well.

Also need to replace 3 of the wire bridges with 75R resistors (termination to ground) and the other 3 with 100R resistors (in series with signal). The 75R are the ones with the distinctly purple/violet end, the 100R are the ones that have black bands in the middle (and brown at the ends). I used permanent markers for the Pr/Pb/ground connections, but didn't have a green marker sorry.




Here is a pic with the inputs attached





This is where those inputs will be connected to. I've modified the side AV input for component! Using a tiny screwdriver I carefully replaced the yellow/red/white facscia with green/blue/red. I also rearranged the connections a little on the back of the PCB (not pictured). Had to add a ground wire and rearrange the connector slightly after taking this photo.




OK, that's all for now. Will be back with more progress soon.

[Zebidee]

So, it all works! here are some shots of it all connected up. On the second pic you can see the standard test colour bars on the screen via PC input.


 


Here is the TV connected to a standard DVD player by component. No GreenAntz required for this, it is completely standard input from the DVD player.


 


Finally, some gratuitous shots of arcade game on a standard CRTEMU PC setup + GreenAntz


   


Please ask questions

[Zebidee]

Finally, a shot of the modded TV with the cover back on, and component input (from PC/CRTEMU + GreenAntz) via side input panel. Neat and tidy, you wouldn't know that it wasn't done in the factory!

[Malenko]

Great write up and great pictures too.

How did you come up with the values for all those resistors and caps, and what do you do if the chassis doesn't have the holes for the caps? I am assuming you just tap the legs of the IC and wire it to a breadboard?

[Zebidee]

Great write up and great pictures too.

How did you come up with the values for all those resistors and caps, and what do you do if the chassis doesn't have the holes for the caps? I am assuming you just tap the legs of the IC and wire it to a breadboard?

Thanks Malenko

I had no specific schematic, but came up with the resistor and capacitor values by looking at many datasheets and schematics for similar TVs with this class of jungle chip. I did a fair bit of experimentation and used an oscilloscope too, not just my eyeballs. Also, this is not the first time I've done this mod for this TV (though definitely the neatest!).

Using 75R for termination is obvious and then 100R in series is very common, in almost every comparable instance I've looked at. Certainly no other value. In any case, the spots were there for the 75R and 100R resistors and there is nothing else that would conceivably go there. And it looks good, better, with scope and eyeballs.

As for the capacitors, 104 (ceramic 0.1uF) is very commonly used after the 100R resistor in similar TV schematics. There are some exceptions of course, one of which is where I've seen a 1uF electrolytic cap used on the Y signal instead of 104, either with or without the 100R resistor. In this case the dead giveaway was the electrolytic cap symbol printed onto the PCB for the Y signal (C803) vs the ceramic cap symbol symbol used for Pb/Pr (C802/801). I later reviewed schematics closer to this TV and changed to 104 ceramic cap for Y as well. So three 104 caps, one each for Y,Pb,Pr. On the virgin chassis PCB, all three just had 103 caps to clamp the unused signal pins. So I whipped out the 103's and replaced with 104 caps.

So I'm confident that I've chosen well for this TV - however other TVs may/will be different. It is a good starting point for your own projects, but won't work exactly the same with every other TV.

You don't necessarily need any breadboard. Probably not, I'd try to avoid it myself. If there aren't too many bits to add, they can be put above or below the PCB. It is also possible to add to twist 2 or more components (e.g. 100R resistor+104 cap in series) together so that they fit into the space for 1 part on the PCB. Grounding 3x75R resistors together isn't too hard either. You can be very creative with this stuff.

I try to keep my work neat and tidy, especially for the pics. But some of the stuff I've prototyped looks like a gymnastics hall. Electronics in 3D.

With all that in mind, it'd be great if other people can contribute with their own component-modding projects.

[Zebidee]

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

[delta88]

This is brilliant!  I have some tvs from the 90s that ive been hoarding with hopes of pulling the case to see if they are candidates for chassis swap for some of my games. shooting from the hip what would you say my odds are of doing something like this to say a 90s zenith , rca?

[Zebidee]

Thanks!

You should do your own research first. Identify model number and chassis number if possible. Identify the jungle IC number and where the inputs are. You should do an online search for datasheets on your jungle IC and schematics. Sometimes you can't find the exact datasheet or schematic for your TV, but one for something close can often suffice.

If you can do an RGB mod, then you are probably better off doing that. Unfortunately you can't do that with all TVs.

YPbPr/component input is almost as good as RGB if you are using the latest GreenAntz RGB to Component Transcoder v1.94. GreenAntz gives much better image quality than the cheap transcoders on Aliexpress (which are actually a substandard ripoff of a leaked old pre-GreenAntz design), which have washed-out color and "flickeryness".

These "China TV" chassis I'm working on are available new, also on Aliexpress, from around $25 each. They will work with most standard 14"-21" CRTs. They give better performance than most cheap arcade monitor RGB chassis that I've used. I've worked on them a lot and gotten to know them pretty well, so can perform most tweaking and repairs myself.

This is brilliant!  I have some tvs from the 90s that ive been hoarding with hopes of pulling the case to see if they are candidates for chassis swap for some of my games. shooting from the hip what would you say my odds are of doing something like this to say a 90s zenith , rca?

[Zebidee]

I noticed a lot of "bleeding" on blue with these last two modded TVs. After investigating many dead ends, I found the solution on the neckboards.

For some reason their neckboards have a 471 (470pF) capacitor (circled in yellow) on the blue drive transistor instead of a 391 (390pF). My earlier modded TVs have a 391 there, and they didn't have the bleeding issue. Don't understand why they used a 471, maybe it looks better that way with TV/composite video input. Looks pretty crap with component input.


 


Anyway, I swapped out the 471 for a 391 and the picture improved significantly, much sharper and less bleeding     I also found a burnt-out resistor (33R) on one, and replaced it with the blue one there (30R, circled in purple). That resistor connects G1 and G2. 30R was the closest value I had available, it seems to be holding up fine.





I'll improve the picture a bit more again by tweaking the service menu. More on that soon.

[Zebidee]

Uploading some info: datasheets, schematics, service mode.

None of this is 100% match for these TVs, but is close enough.

To access service mode:
- press MENU
- press 2,4,8,3 - the word "FACTORY" should appear.
- press DISP

This gets you to page 0, "white balance", of the service menu. Press number keys to change page. To go above page 3, find "PAGE" and flip the value to "1". Press MUTE to go up one page. AFAIK this is the only way to access pages above 9.

[Zebidee]

More China TV datasheet/schematics/service mode info that would not fit in last post. Attached as a zip file.