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 Post subject: Sony KV13TR24 - Tapping the Neckboard
PostPosted: Thu Apr 12, 2018 6:05 am 


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Joined: 20 Mar 2018
Posts: 14
There seems to not be a lot of info on how to do this correctly. I can understand why. Generally there's better ways to do this and the neckboard route is usually last resort. But that's not gonna be the case for me. I can't do it any other way with the TV I want to do this on.

So I'll go ahead and make a thread about this.

I'm going to RGB mod a Sony KV13TR24. This TV does not have close captioning (it was made in 1990 before the US passed the law requiring CC for a 13+ inch TVs) and the OSD's RGB output is incomplete (Blue channel terminates into a filter cap and doesn't go anywhere).

Jungle IC does not have RGB input for OSD. OSD's RGB gets amplified via a couple transistors (one for each channel) which then passes through diodes before merging with the Jungle IC's RGB output.

All this hot mess then goes to the neckboard. :P

So basically my plan is to replicate what the OSD circuit is doing. I need to take 0.1ish volt RGB from SCART compatible RGB (currently have a Sega Genesis model 2 I can test this with) and amplify it to the 3 volts that the neckboard expects. I've seen one other person do something like this:

http://web.archive.org/web/201603270526 ... /wp/?p=284

He however did not provide RGB at the correct output for the neckboard's drive transistors so contrast wasn't that great. He got a mostly acceptable picture from just feeding it standard RGB it seems. So this could work out well for me if I go the extra mile and build a circuit that outputs to the correct voltage level.

The Jungle IC outputs direct to the neckboard. There's only a single resistor for each channel that the signal goes through before going to the neckboard.

Also I have a whole second board and neckboard for this TV. Interesting story about this but I'll save that for the end of this post so you won't be forced to read that if you're not interested. :P

So I'll cut to the chase and post the schematics:


Full Board:
https://i.imgur.com/OgkHKbz.png

How the OSD gets muxed into the Jungle IC's output:

Image

It gets amplified through through that transistor pair. Schematic seems to indicate that Jungle IC outputs RGB at 3 volts. That's what I'm wanting to replicate here. My goal is to convert standard RGB to the 3.0 volts the schematic calls for at the neckboard's drive transitors input. I have a whole second pair of cable and jacks I can solder together to tap into the neckboard without soldering anything to the working board/neckboard.


I've heard issues can arise if the neckboard isn't connected to the board. But this TV is ancient and I'm sure it can handle not having the jungle IC's RGB connected when ever I'm using external RGB source.
I don't plan to disconnect the 9v power, sub-brightness line, and ground wire. Though I may use the ground wire as part of the ground for my RGB source. If it's safe to do so? It seems to be isolated from the CRT's ground line/pin well enough. I'm talking about the ground wire that is part of the main neckboard connector going to the board. Not the CRT ground wire. (lol tapping that would be a bad idea. :P )

Only thing I'm not sure about is if this TV is isolated from mains properly. The full schematic shows how the power supply side of the board is configured. Should be able to tell if ground is isolated or not.

If I do use a set of transitors matching what the OSD circuit uses, I just have to feed them the 9ish volts the circuit originally called for and I'll get the 3volt output I want? If there's an existing circuit design for a neckboard mod out there I'd like to see that as well. Any input on this would be apprecieted. I haven't bought any parts to do this yet, but need a good plan in place before I get to that step. :D

I could setup my mod to include OSD's output...but the OSD on this TV is very simple and only has controls for timer, channel setup of RF tuner, and basic picture controls. And the picture controls won't do anything when using external RGB so yeah...I don't need OSD on my external RGB source. :P


Now for the TLDR story on how/why I acquired this TV:

Spoiler: show
I first purchased a KV13TR24 a few weeks ago. But it arrived damaged in shipping. CRT neck broke due to bottom mounts breaking and causing tube to pivot up causing neckboard to hit the case. This cracked the neckboard nearly in half and broke the tube. The TV was a total loss nearly so I contacted seller about this. He refunded and didn't ask for me to send it back. So I took the board out (it seemingly survived. no cracks near the flyback or anything) and the neckboard as well. The neckboard cracked along several traces so it would be a pain to try and fix but kept it incase I needed the components on it.

I bought this TV before I found the correct service manual. At first I could only find the manual to a KV13TR28. So initially thought it was going to be an easy RGB mod via closed caption module. Nope. After I got the TV I found the correct manual (the manual is for a kv43tr27 but first page listed my TV as one of the two other models with the same chassis and covered by the same service manual. This TV does not have a service menu. Most of the geometry adjustments are old school variable resistor trim pots and there is no close captioning feature.

So I got the second tv (the one I currently own) from a different seller. Even though it was going to be harder to mod I figured I'd rather just get one I got a whole set of parts for then go for a different model. That way I have many backup parts incase stuff breaks. I have a limited income and my area sucks. Can't find any Sony tvs of this size for sale locally. Pretty much have to acquire one from eBay. :(


Well...This TV arrived DOA as well. It's main board had a crack near the flyback that disrupted two traces. Interestingly there was already a bodge wire bypassing the crack so this was like this prior to shipment? Well they didn't fix the trace for one of the pins going to the deflection coil.

Anyways so yet another return case opened. Again like last time the seller refunded. Didn't ask to send it back either. So now I have one with a dead board but a CRT that survived and a repairable neckboard. Kinda wish I decided to keep the case to the last TV. It's in a bit better shape then this one as there is also a small crack in the bottom right corner. :P

Also just like the last tv the bottom crt mounts broke. But since the seller packed this TV very well, the tube survived. Neckboard cracked like the last one and detached from the neck of the tube partially. But the crack on the neckboard was at a different angle and was smaller. Only had to solder bridge wires across 3 traces. Then swapped out the dead board with the one from the previous TV. Could not get the original board to do anything despite bridging a broken trace going from the flyback to one of the pins to the deflection coil connection. Relay switch doesn't do anything so it doesn't even attempt to power on. Decided not to waste time on it and just swap in the board from the last TV.

By some miracle the damn thing works! I don't get how the board from the last TV survived despite being poorly packed and shipped by USPS who seemed more then happy to toss this around in shipping. I adjusted a few of the trim pots and now it looks pretty much like it should. The deflection coil seems to not have been disturbed either so didn't have to mess with the convergance. Tube produces great picture. But the composite input...is well flawed by design. Would like to RGB mod this thing.


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 Post subject: Re: Sony KV13TR24 - Tapping the Neckboard
PostPosted: Fri Apr 13, 2018 5:10 pm 


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Joined: 09 Mar 2017
Posts: 35
I've got a similar set (KV-27ts30) I posted about in the main thread. My plan was to remove the inline resistors on the jungle RGB out, hook up a switch to those points, and run my external RGB in through a ths7316 and some pots to get the voltage right. I've been unable to move forward on this as my parts haven't arrived yet, but I can't see any reason this shouldn't work, unless the 7316 outputs a lower voltage than I thought.

I've looked at eviltim's vga to arcade monitor circuit, which may be what you're after, but I'm not sure it's entirely necessary? seems a bit like overkill but maybe I'm underthinking it.
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 Post subject: Re: Sony KV13TR24 - Tapping the Neckboard
PostPosted: Fri Apr 13, 2018 7:24 pm 


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Joined: 20 Mar 2018
Posts: 14
Ahh I see. My plan was to go solderless in regards to changes to the neckboard/main PCB. I'd have the main cable go into a second cable that is connected to a switch for either allowing output from Jungle IC or output from my ext. source. As the OSD on my TV is pretty ancient and limited I have no desire to have that usable with the external source. Though if my method of using only cables to interrupt/tap the RGB input of the neckboard produces issues, then I could desolder the resistors and do it like you plan to do. I guess I'd have the benefit of having usable OSD that way for what that's worth. :P

The Jungle IC uses 330ohm resistors in series with each RGB channel before it goes to the neckboard. So looks like that will be something I add to the design. Looks like the direct coupled video amplifier is what I'm looking to use here? Should be easy enough.

Only hardpart is translating that circuit diagram. If you manage to build one like this on your TV, let me know how it went and give me some good photos of how the parts are arranged. That would help me get my circuit organized correctly. :D

There's two circuits on that page though. Direct Coupled Video amplification and AC coupled version. I assume in this instance I'll be using the DC Coupled one correct? My sync input will use the Composite video input this TV already has.


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 Post subject: Re: Sony KV13TR24 - Tapping the Neckboard
PostPosted: Sun May 06, 2018 2:01 am 


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Ok, around June 3rd I plan to order the rest of the parts I need. I built this pass through cable for the neckboard:

https://i.imgur.com/CVnvT7Y.jpg
(I pulled the male connector off the dead neckboard from the spare TV parts from the first DOA TV I had gotten from eBay as well as the cable itself. The image shows the dead neckboard with the connector positioned roughly where it will be on the neckboard installed in the TV to show how the connection will work)

I soldered the connector then stabilized it with hotglue.

With that I don't need to solder anything to the either the main PCB or the neckboard. I did a basic test where I just put the wires directly into the Genesis's RGB pins and used composite video for sync (tested clean sync pin, doesn't work so will need to use composite video for sync source). With both sharing ground. Ground to AV port needs to be connected else I don't get sync.

I get a dark but clean image from what I can tell. The image becomes bright and visible when turning off the TV. (so just as the deflection shuts down I see a bright and clean image as the image shrinks).

So yeah looks like I will need to amplify it and it will then work. Once I amplify the signal with the correct impedenace (and probably need to run it through capacitors, but the dark image didn't have any noise in it. So may not need that. But the prebuilt amp boards I got in my eBay watch list have the needed caps. Though the outputs for them are 75ohm terminated on the output. I can pull those resisters off the board if they cause issues. I will then just run RGB output through 330ohm resistors to get the correct impedance this neckboard expects. (as that's what the schematic has the jungle IC outputs going through). The 330 ohm resistors are in series and not terminated to ground FYI and there's no capacitors connected according to the schematic.

Also during my test connection, the TV did not have brightness issues (was dark but stable) and didn't see any raster lines appear at all. The TV did not auto shutdown at any point either. So as expected this old 1991 TV doesn't have any of the advanced balancing circuitry the newer TVs have so tapping the neckboard in this way shouldn't cause any issues. At least for this model TV. :D


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