TV RGB mod thread

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InfamousSabre
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Re: TV RGB mod thread

Post by InfamousSabre »

Ryeno wrote:
InfamousSabre wrote:
I'm getting started on that right now. The micon is socketed so I'd hoped to just unsocket it, bend up the 3 output pins, then resocket, but its stuck in there pretty tight and theres a metal shield all around it so I cant slip a screwdriver underneath to pry it up like usual. Going to just desolder that first resistor (3310, 3318, 3320) to disconnect the micon from the rest of that circuit. Then, on the jungle side, that 1uf capacitor is through-hole so ill pull up the micon-facing leg, removing the jungle from the circuit. After that I can get wires running out to a breadboard and look at creating the mux circuit like you said.

At the micon, on the RED-OSD, GRN-OSD, and BLU-OSD pins, it says 0V. If there's 0 volts coming out of those pins, how on earth does it work? Or am I just reading it improperly?

Easiest way to RGB mod is to use as 4PDT Switch at the 1uF input caps. This method will work 100% but you'll lose OSD in RGB mod.

The other option is to remove 120 ohm grounding resistors and replace them with 75 ohm and 39 ohm and inject RGB between the 2 resistors. Is the Micon 5V or 7.5V?
Just checked and the micon is 5.0V
MarkOZLAD
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Re: TV RGB mod thread

Post by MarkOZLAD »

InfamousSabre wrote:Alright I'm back again with yet another set. This is a GE 20GH250 with a CTC-176K2 chassis utilizing a Sanyo LA7610 jungle chip.
The schematic for this TV looks really odd to me though. I cant quite understand where I should inject RGB. Can anyone help me out here?

Image
Ok, I'll try again.

If it's a 5V micom that is sending OSD high pulses...

Using the green circuit as an example.

I would remove R3317, R2712 and Q2701. I would short between the holes left by the base and collector of Q2701. This should leave us muxing with 1100 ohm factory in-lines. Then I run my 75 ohm terminated external G into a 110 ohm mux resistor and connect it somewhere betwen R2713 and C2707...Perhaps I would connect to the place where I shorted the transistor holes or possibly a twist method 110R and 75R, 75R has leg into emitter hole of Q2701, 110R has leg in Collector hole.
Last edited by MarkOZLAD on Sat Jul 02, 2022 3:16 pm, edited 1 time in total.
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maxtherabbit
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Re: TV RGB mod thread

Post by maxtherabbit »

0V is the nominal voltage on the pin i.e. when the OSD is not active
MarkOZLAD
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Re: TV RGB mod thread

Post by MarkOZLAD »

maxtherabbit wrote:0V is the nominal voltage on the pin i.e. when the OSD is not active
I made a typo on my post. I meant 5V micom.

Assuming micom is sending 5V when OSD is on, 0V when off.
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"Imagine toggle switch OSD modding a TV in 2019" - maxtherabbit
Ryeno
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Re: TV RGB mod thread

Post by Ryeno »

MarkOZLAD wrote:
InfamousSabre wrote:Alright I'm back again with yet another set. This is a GE 20GH250 with a CTC-176K2 chassis utilizing a Sanyo LA7610 jungle chip.
The schematic for this TV looks really odd to me though. I cant quite understand where I should inject RGB. Can anyone help me out here?

Image
Ok, I'll try again.

If it's a 5V micom that is sending OSD high pulses...

Using the green circuit as an example.

I would remove R3317, R2712 and Q2701. I would short between the holes left by the base and collector of Q2701. This should leave us muxing with 1100 ohm factory in-lines. Then I run my 75 ohm terminated external G into a 110 ohm mux resistor and connect it somewhere betwen R2713 and C2707...Perhaps I would connect to the place where I shorted the transistor holes or possibly a twist method 110R and 75R, 75R has leg into emitter hole of Q2701, 110R has leg in Collector hole.

There is a good chance the MICON can't directly drive the OSD which is why the engineers put the transistors between it and the jungle chip. It's not likely that the engineers simply over-engineered this set. For this reason it makes more sense to simply mux into the base of the transistor and if that doesn't work then use a 4PDT switch without mux.

https://imgur.com/ZvZXpt5
Green is Micon, Blue is output to Jungle.
MarkOZLAD
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Re: TV RGB mod thread

Post by MarkOZLAD »

Fair call.

I’d like to see if there are any other schematics around that show the same chips in use.
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"Imagine toggle switch OSD modding a TV in 2019" - maxtherabbit
InfamousSabre
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Re: TV RGB mod thread

Post by InfamousSabre »

Ryeno wrote:
InfamousSabre wrote:
I'm getting started on that right now. The micon is socketed so I'd hoped to just unsocket it, bend up the 3 output pins, then resocket, but its stuck in there pretty tight and theres a metal shield all around it so I cant slip a screwdriver underneath to pry it up like usual. Going to just desolder that first resistor (3310, 3318, 3320) to disconnect the micon from the rest of that circuit. Then, on the jungle side, that 1uf capacitor is through-hole so ill pull up the micon-facing leg, removing the jungle from the circuit. After that I can get wires running out to a breadboard and look at creating the mux circuit like you said.

At the micon, on the RED-OSD, GRN-OSD, and BLU-OSD pins, it says 0V. If there's 0 volts coming out of those pins, how on earth does it work? Or am I just reading it improperly?

Easiest way to RGB mod is to use as 4PDT Switch at the 1uF input caps. This method will work 100% but you'll lose OSD in RGB mod.

The other option is to remove 120 ohm grounding resistors and replace them with 75 ohm and 43 ohm and inject RGB between the 2 resistors. Is the Micon 5V or 7.5V?
So, using Green as an example, this is all I need to do for the RGB lines?
Image
MarkOZLAD
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Re: TV RGB mod thread

Post by MarkOZLAD »

InfamousSabre wrote:
Ryeno wrote:
InfamousSabre wrote:
I'm getting started on that right now. The micon is socketed so I'd hoped to just unsocket it, bend up the 3 output pins, then resocket, but its stuck in there pretty tight and theres a metal shield all around it so I cant slip a screwdriver underneath to pry it up like usual. Going to just desolder that first resistor (3310, 3318, 3320) to disconnect the micon from the rest of that circuit. Then, on the jungle side, that 1uf capacitor is through-hole so ill pull up the micon-facing leg, removing the jungle from the circuit. After that I can get wires running out to a breadboard and look at creating the mux circuit like you said.

At the micon, on the RED-OSD, GRN-OSD, and BLU-OSD pins, it says 0V. If there's 0 volts coming out of those pins, how on earth does it work? Or am I just reading it improperly?

Easiest way to RGB mod is to use as 4PDT Switch at the 1uF input caps. This method will work 100% but you'll lose OSD in RGB mod.

The other option is to remove 120 ohm grounding resistors and replace them with 75 ohm and 43 ohm and inject RGB between the 2 resistors. Is the Micon 5V or 7.5V?
So, using Green as an example, this is all I need to do for the RGB lines?
Image
So you think the transistor will linearly amplify the external RGB? Very cool if it does.
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MarkOZLAD
OSD/External RGB Mux Diagram
OSD/External RGB Mux Resistor Value Table 0.7Vp-p : 0.5Vp-p

"Imagine toggle switch OSD modding a TV in 2019" - maxtherabbit
Ryeno
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Re: TV RGB mod thread

Post by Ryeno »

InfamousSabre wrote:
Ryeno wrote:
InfamousSabre wrote:
I'm getting started on that right now. The micon is socketed so I'd hoped to just unsocket it, bend up the 3 output pins, then resocket, but its stuck in there pretty tight and theres a metal shield all around it so I cant slip a screwdriver underneath to pry it up like usual. Going to just desolder that first resistor (3310, 3318, 3320) to disconnect the micon from the rest of that circuit. Then, on the jungle side, that 1uf capacitor is through-hole so ill pull up the micon-facing leg, removing the jungle from the circuit. After that I can get wires running out to a breadboard and look at creating the mux circuit like you said.

At the micon, on the RED-OSD, GRN-OSD, and BLU-OSD pins, it says 0V. If there's 0 volts coming out of those pins, how on earth does it work? Or am I just reading it improperly?

Easiest way to RGB mod is to use as 4PDT Switch at the 1uF input caps. This method will work 100% but you'll lose OSD in RGB mod.

The other option is to remove 120 ohm grounding resistors and replace them with 75 ohm and 43 ohm and inject RGB between the 2 resistors. Is the Micon 5V or 7.5V?
So, using Green as an example, this is all I need to do for the RGB lines?
Image
That should work as long as the MICON resistor is 1k and not 3k and it isn't doing anything weird like grounding the output when not in use.

If it works, you could also increase the filter capacitor from 22pF to 10nF. That would decrease interferance.
abispac
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Re: TV RGB mod thread

Post by abispac »

Ok new attemp, this time a disney mikey mouse tv dt1350-c model, should be an easy mod, but because its a componets on the board type, and not the holes type, ill have to pay someone to solder some cables for me. Anyway, i saw the segaholic performing a mod but it looks to complicated with the switch and stuff, and with the new example (new for me) i saw from markozlad, i think i understud how to perform this. So heres a mockup o my model

Image

The new example tells me where to inject the rgb signal, but i still need to understand, how do i keep the 5v from going to the micon, so it wont fry it over time? do we still use a switch for that or am i missing something? im gonna go read the whole topci againg to find out. But if anyone cares to answer ill apreciate it.

Now i need to photoshop the cables at my service manul picture so i know where to solder the cables.
Ill keep this updated, thanks
KPackratt2k
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Re: TV RGB mod thread

Post by KPackratt2k »

abispac wrote:Ok new attemp, this time a disney mikey mouse tv dt1350-c model, should be an easy mod, but because its a componets on the board type, and not the holes type, ill have to pay someone to solder some cables for me. Anyway, i saw the segaholic performing a mod but it looks to complicated with the switch and stuff, and with the new example (new for me) i saw from markozlad, i think i understud how to perform this. So heres a mockup o my model

https://klovimg.com/image/CqEXp

The new example tells me where to inject the rgb signal, but i still need to understand, how do i keep the 5v from going to the micon, so it wont fry it over time? do we still use a switch for that or am i missing something? im gonna go read the whole topci againg to find out. But if anyone cares to answer ill apreciate it.

Now i need to photoshop the cables at my service manul picture so i know where to solder the cables.
Ill keep this updated, thanks
Here's my modding schematic for this chassis based on MarkOZLAD's recommendations:
Image
Even if you're using SCART, I would still recommend using a switch for blanking because not all cables handle blanking. If you insist on blanking via SCART, you can try adding a diode on the blanking wire.

If you have more than one of these TVs and wouldn't mind parting one of them out for me, let me know. I have a Mickey TV that suffered from a vertical IC failure and I wasn't able to fix its chassis. I would love to get mine working again.
abispac
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Re: TV RGB mod thread

Post by abispac »

KPackratt2k wrote:
abispac wrote:Ok new attemp, this time a disney mikey mouse tv dt1350-c model, should be an easy mod, but because its a componets on the board type, and not the holes type, ill have to pay someone to solder some cables for me. Anyway, i saw the segaholic performing a mod but it looks to complicated with the switch and stuff, and with the new example (new for me) i saw from markozlad, i think i understud how to perform this. So heres a mockup o my model

https://klovimg.com/image/CqEXp

The new example tells me where to inject the rgb signal, but i still need to understand, how do i keep the 5v from going to the micon, so it wont fry it over time? do we still use a switch for that or am i missing something? im gonna go read the whole topci againg to find out. But if anyone cares to answer ill apreciate it.

Now i need to photoshop the cables at my service manul picture so i know where to solder the cables.
Ill keep this updated, thanks
Here's my modding schematic for this chassis based on MarkOZLAD's recommendations:
Image
Even if you're using SCART, I would still recommend using a switch for blanking because not all cables handle blanking. If you insist on blanking via SCART, you can try adding a diode on the blanking wire.

If you have more than one of these TVs and wouldn't mind parting one of them out for me, let me know. I have a Mickey TV that suffered from a vertical IC failure and I wasn't able to fix its chassis. I would love to get mine working again.
Why did you use 750 instead of 510 as sugested in the Markozlad guide? And let me see if can get one chassis for you, this tvs are common on my city, i live at the border with texas and today i got this one for 10dlls, i have bought some in the past but they where diferent inside. Still the same mod could have been perfomed.
MarkOZLAD
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Re: TV RGB mod thread

Post by MarkOZLAD »

abispac wrote: Why did you use 750 instead of 510 as sugested in the Markozlad guide? And let me see if can get one chassis for you, this tvs are common on my city, i live at the border with texas and today i got this one for 10dlls, i have bought some in the past but they where diferent inside. Still the same mod could have been perfomed.
I'm not sure what I put in the guide but if the OSD inlines are 4700 Ohm my lookup table for 0.7V no diodes says 750 Ohm mux.
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thchardcore
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Re: TV RGB mod thread

Post by thchardcore »

Just curious, but why are the Disney TVs so popular? Seems like everyone wants one.
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maxtherabbit
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Re: TV RGB mod thread

Post by maxtherabbit »

thchardcore wrote:Just curious, but why are the Disney TVs so popular? Seems like everyone wants one.
meme tv
abispac
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Re: TV RGB mod thread

Post by abispac »

MarkOZLAD wrote:
abispac wrote: Why did you use 750 instead of 510 as sugested in the Markozlad guide? And let me see if can get one chassis for you, this tvs are common on my city, i live at the border with texas and today i got this one for 10dlls, i have bought some in the past but they where diferent inside. Still the same mod could have been perfomed.
I'm not sure what I put in the guide but if the OSD inlines are 4700 Ohm my lookup table for 0.7V no diodes says 750 Ohm mux.
Arent we using 5v instead of 7v? if is 5v then the guiide says to use 510ohms instead

Thats another thing i still dont understand, is o.5 = to 5v and 0.7 =7v? or does it mean something else?
The segaholic guy , uses 5v , so i though using the 510 ohms whats the correct way. but if Markozlad told you to use 750, then i guess ill use 750 ones.
Last edited by abispac on Mon Jul 04, 2022 7:56 pm, edited 1 time in total.
abispac
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Re: TV RGB mod thread

Post by abispac »

thchardcore wrote:Just curious, but why are the Disney TVs so popular? Seems like everyone wants one.
Well, i got this obsesion to build a couple of small arcades with 13 inch monitors, but real arcade monitors that size are betwen 250 dlls and up, not to ention the chassis are way to old and use and they a pain in the ass, they break real easy and wont last long. tvs on the other side, i find them to have a better shape, no broken solders, the parts last longer as they have not been abused. so im giving this small tvs a better chanse than arcade monitors, plus the picture looks nice. thas my personal opinion.
PressLeft
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Re: TV RGB mod thread

Post by PressLeft »

I just picked up a Philips 19PS40 and think it's a great candidate for an RGB mod as the composite quality really stunned me when i first turned it on. This will be my first time RGB modding, but i've modded consoles and repaired speakers and CRTs before so i'm not a complete noob.

I've found the relevant service docs and uploaded them to archive.org here: https://archive.org/details/7602_20220703

Starting on page 96 of 7602.pdf we've got the schematics that can help us figure this out before opening it up. I will open it up and take photos of the board later. These docs are for the chassis this uses, but i've got a consumer set so there's a bunch of unused stuff on the board.

My set only has composite on the front (with headphone out) and RF on the back. My primary goal is to add RGB; there isn't much room to add those ports on the front near the existing composite, so adding another composite for sync on the back would be ideal. I'd love to replace the RF with composite and use that for sync. Doing that would also require adding audio jacks on the back as well though.

So I believe this means I need to get myself some BNC jacks and RCA jacks. I've got wire and resistors and soldering tools already. Anything else i'm missing before i crack this open and photograph the board?
Ryeno
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Re: TV RGB mod thread

Post by Ryeno »

PressLeft wrote:I just picked up a Philips 19PS40 and think it's a great candidate for an RGB mod as the composite quality really stunned me when i first turned it on. This will be my first time RGB modding, but i've modded consoles and repaired speakers and CRTs before so i'm not a complete noob.

I've found the relevant service docs and uploaded them to archive.org here: https://archive.org/details/7602_20220703

Starting on page 96 of 7602.pdf we've got the schematics that can help us figure this out before opening it up. I will open it up and take photos of the board later. These docs are for the chassis this uses, but i've got a consumer set so there's a bunch of unused stuff on the board.

My set only has composite on the front (with headphone out) and RF on the back. My primary goal is to add RGB; there isn't much room to add those ports on the front near the existing composite, so adding another composite for sync on the back would be ideal. I'd love to replace the RF with composite and use that for sync. Doing that would also require adding audio jacks on the back as well though.

So I believe this means I need to get myself some BNC jacks and RCA jacks. I've got wire and resistors and soldering tools already. Anything else i'm missing before i crack this open and photograph the board?

https://pdf1.alldatasheet.com/datasheet ... A955X.html

It appears this jungle chips takes both YUV and RGB through the same pins. I'm not sure how it selects between the 2, might be a firmware setting.
PressLeft
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Re: TV RGB mod thread

Post by PressLeft »

Ryeno wrote: It appears this jungle chips takes both YUV and RGB through the same pins. I'm not sure how it selects between the 2, might be a firmware setting.
any way for me to do some probing to find out?
PressLeft
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Re: TV RGB mod thread

Post by PressLeft »

PressLeft wrote:
Ryeno wrote: It appears this jungle chips takes both YUV and RGB through the same pins. I'm not sure how it selects between the 2, might be a firmware setting.
any way for me to do some probing to find out?
actually, according the service manual:

"The output of the YUV separator is fed to the internal YUV switch, which switches between the output of the YUV separator or the external YUV (for DVD or PIP) on pins 51-53. Pin 50 is the input for the insertion control signal called 'FBL-1'. When this signal level becomes higher than 0.9 V (but less than 3 V), the RGB signals at pins 51, 52 and 53 are inserted into the picture by using the internal switches"
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matt
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Re: TV RGB mod thread

Post by matt »

Ryeno wrote:
PressLeft wrote:I just picked up a Philips 19PS40 and think it's a great candidate for an RGB mod as the composite quality really stunned me when i first turned it on. This will be my first time RGB modding, but i've modded consoles and repaired speakers and CRTs before so i'm not a complete noob.

I've found the relevant service docs and uploaded them to archive.org here: https://archive.org/details/7602_20220703

Starting on page 96 of 7602.pdf we've got the schematics that can help us figure this out before opening it up. I will open it up and take photos of the board later. These docs are for the chassis this uses, but i've got a consumer set so there's a bunch of unused stuff on the board.

My set only has composite on the front (with headphone out) and RF on the back. My primary goal is to add RGB; there isn't much room to add those ports on the front near the existing composite, so adding another composite for sync on the back would be ideal. I'd love to replace the RF with composite and use that for sync. Doing that would also require adding audio jacks on the back as well though.

So I believe this means I need to get myself some BNC jacks and RCA jacks. I've got wire and resistors and soldering tools already. Anything else i'm missing before i crack this open and photograph the board?

https://pdf1.alldatasheet.com/datasheet ... A955X.html

It appears this jungle chips takes both YUV and RGB through the same pins. I'm not sure how it selects between the 2, might be a firmware setting.
These jungle chips can process both signals, but on US models the RGB is locked out in firmware.

Many of these can be modded to accept component video, though, and the quality is very good. I made a writeup of how to do it on a similar TV. The process on the TDA955X jungle chips basically the same, although the pinout is different:

https://crtdatabase.com/crts/magnavox/m ... 4ms2331-17

However, one complication is that some of these TVs don't have a service menu. For those models, you have to use an obtuse factory remote that's difficult to find and confusing to use. I have a Philips 19PS50 that I was able to modify this way, but unless you can find the remote you're SOL.

So, the first step with the mod would be to try entering the service menu using an ordinary remote. If you can do that, the mod may be possible. Press "0, 6, 2, 5, 9, 6, Menu" on the remote and see if it works.
MarkOZLAD
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Re: TV RGB mod thread

Post by MarkOZLAD »

PressLeft wrote:
PressLeft wrote:
Ryeno wrote: It appears this jungle chips takes both YUV and RGB through the same pins. I'm not sure how it selects between the 2, might be a firmware setting.
any way for me to do some probing to find out?
actually, according the service manual:

"The output of the YUV separator is fed to the internal YUV switch, which switches between the output of the YUV separator or the external YUV (for DVD or PIP) on pins 51-53. Pin 50 is the input for the insertion control signal called 'FBL-1'. When this signal level becomes higher than 0.9 V (but less than 3 V), the RGB signals at pins 51, 52 and 53 are inserted into the picture by using the internal switches"
I've found that these chips tend to be locked into either component or RGB modes. Normally if locked into component you'll see the pin 50 wired permanently to a voltage source. I've also seen the pin 50 wired to ground but then if you try and use the RGB it's locked out.
Last edited by MarkOZLAD on Tue Jul 05, 2022 1:42 am, edited 1 time in total.
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"Imagine toggle switch OSD modding a TV in 2019" - maxtherabbit
PressLeft
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Re: TV RGB mod thread

Post by PressLeft »

matt wrote: These jungle chips can process both signals, but on US models the RGB is locked out in firmware.

Many of these can be modded to accept component video, though, and the quality is very good. I made a writeup of how to do it on a similar TV. The process on the TDA955X jungle chips basically the same, although the pinout is different:

https://crtdatabase.com/crts/magnavox/m ... 4ms2331-17

However, one complication is that some of these TVs don't have a service menu. For those models, you have to use an obtuse factory remote that's difficult to find and confusing to use. I have a Philips 19PS50 that I was able to modify this way, but unless you can find the remote you're SOL.

So, the first step with the mod would be to try entering the service menu using an ordinary remote. If you can do that, the mod may be possible. Press "0, 6, 2, 5, 9, 6, Menu" on the remote and see if it works.
I'm able to access the service menu. it seems like if i add the hardware I can enable component/RGB by turning on AV3 from the option bytes in the service menu. To enable RGB it seems like i'll just need a switch to a ~1.1v power source to pin 50 to switch from YUV to RGB.
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matt
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Re: TV RGB mod thread

Post by matt »

That's not how it works. Adding that voltage to pin 50 is necessary to enable YUV, but it still doesn't enable RGB.

You'll have to look up the correct option bit value in the service menu to enable component input. If it works, it will say "CVI" when you select the correct input and you'll be able to proceed with the rest of the mod. What was the default value of OP5?

Some models have the CVI option disabled, though, so it's not possible with all of these sets.

On most of these TVs, there's an empty resistor pad that you can just populate to add the correct switching voltage.
PressLeft
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Re: TV RGB mod thread

Post by PressLeft »

dang, still component is great and i'll take it. I'll also add s-video while i'm at it; your guide is excellent.

default value of OP5 is 144.

edit: originally put 180, but that contradicts what's in the service manual. odd, since i didn't put it at 180 myself.
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matt
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Re: TV RGB mod thread

Post by matt »

Ok, 144 makes a lot more sense. Try changing it to 156 and see if you can switch to Svideo and CVI modes.
PressLeft
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Re: TV RGB mod thread

Post by PressLeft »

156 didn’t get me SVHS or CVI, but it did get me “X 1” as a channel in addition to me “FRONT” AV option (i believe this is AV3).

Some other values enabling AV and AV2 (202) did get me a really bizarre moving black and white triangle pattern. Seen here: https://i.imgur.com/ln4k6cl

This pattern gets a little more erratic when input is provided to the front composite, which makes me think this might be S-video? It could also be the sync signal for RGB? Idk, but it’s definitely some portion of a signal for another type of input that hardware is missing for.

Actually, after fiddling with it a bit, I also saw “X AV” after switching back from 202 to 156. I suspect “X” is actually just a signifier that the currently selected input has been disabled. If you CH+/- away from it you can’t return to it unless you change the options to enable it again.

Edit:
I decided to try enabling everything but hotel and PIP modes by entering 252 for OP5. This got me the following results:
- AV1: black and white triangle pattern linked above; this is affected somehow by the input on the front
- AV2: duplicates Front input
- Front: the composite input on the front as expected
- RF

I suspect that this means:
- AV1 is component or RGB; my reasoning is that the image changes from receiving a signal on front input, which would indicate that’s some portion of the signal, like sync
- AV2 is s-video; my reasoning is that it duplicates the front signal, which would appear identical to composite if chroma & luma were being combined
- Front is AV3 as documented.
abispac
Posts: 73
Joined: Sun Mar 29, 2020 3:44 am

Re: TV RGB mod thread

Post by abispac »

Does anyone besides Markozlad, as i dont want to burn him down, care to explain how do we know if the tv is 0.7 or 0.5 ? Thanks for your time.
Ryeno
Posts: 89
Joined: Tue Nov 05, 2019 6:50 am

Re: TV RGB mod thread

Post by Ryeno »

abispac wrote:Does anyone besides Markozlad, as i dont want to burn him down, care to explain how do we know if the tv is 0.7 or 0.5 ? Thanks for your time.

Use the voltage divider calculator.
https://ohmslawcalculator.com/voltage-d ... calculator
Subtract 0.7v from the input voltage if there is a diode on the line.
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