JVC 36" AV36850 RGB mux Mod / TA1242N Jungle / New Mod Video

[deezdrama]

Update.....7-18-22........
Finally had time to edit a youtube video on this mod....
https://youtu.be/OBiB3B4Z0qs





Original post....
So I had some free time to crack open Bertha today, Was hoping to be able to identify the tube but the serial number on this 1997 pre D series 850 model lacks the letter code.
Any ideas how to identify the make of this tube?









Had a crapton of dust, I took the board and back casing outside and used air compressor, used the vacuum with brush attachment on the tube housing.

Pretty cool that the chassis board has a removable plastic carrier frame like a pvm!
I got the micon and jungle marked according to the service manual.




Thats about as far as I made it today.
Hey Mark..... Do you think Im better off doing the hack and button mod on this one? I know you said the jungle expects 0.5Vp-p on this one..... Or is that not too difficult to do?

[matt]

I'm not on expert on this, but those bonded yoke tubes usually are from RCA/Thompson. They give a beautiful picture but the downside is that you can't do much to fix convergence errors.

[deezdrama]

I'm not on expert on this, but those bonded yoke tubes usually are from RCA/Thompson. They give a beautiful picture but the downside is that you can't do much to fix convergence errors.

Your right, did some archive searches and that tube number was held in patent 97 to 2001... Says RCA/Thompson

So was RCA/Thompson a single entity? I always hear people talking about having the thompson tubes in their JVC d-series but assumed it was a company seperate from RCA. Or were they merged for a short while and later seperated, or was this model tube being produced by both companies and its one or the other?

I read some of the d series tubes were m class, anyone know which make of tubes those were?

[matt]

Thompson bought the RCA brand in the '80s and took over their tube production. IIRC they didn't sell TVs under their own name in the US and most of their products were labeled RCA.

Panasonic sold tubes with model numbers beginning in M. Some of these were apparently used by JVC. They are just regular consumer tubes however and aren't particularly special.

[deezdrama]

Thompson bought the RCA brand in the '80s and took over their tube production. IIRC they didn't sell TVs under their own name in the US and most of their products were labeled RCA.

Panasonic sold tubes with model numbers beginning in M. Some of these were apparently used by JVC. They are just regular consumer tubes however and aren't particularly special.

Ah ok. Ive read in the past people claiming some acrade monitors and tubes in JVC's had M class tubes versus A class.... supposedly were made to a better standard.... IDK, maybe they were talking out of their ass lol

[kitty666cats]

I have one of these http://mikejmoffitt.com/articles/0051-nettv-rgb.html and it used a Toshiba “M” monitor grade ‘Microfilter’ tube / it’s definitely quite nice. So it kinda seems like an M is sometimes an indication of a higher-end tube… but not always? Very confusing. I have not seen many, in general! Wonder what the NEC and Mitsubishi presentation monitor tubes have for the model #…

[deezdrama]

I have one of these http://mikejmoffitt.com/articles/0051-nettv-rgb.html and it used a Toshiba “M” monitor grade ‘Microfilter’ tube / it’s definitely quite nice. So it kinda seems like an M is sometimes an indication of a higher-end tube… but not always? Very confusing. I have not seen many, in general! Wonder what the NEC and Mitsubishi presentation monitor tubes have for the model #…

Awesome! I dont know about the NEC or Mitsubishis, Ive always kept an eye out for them but never seen one listed anywhere near here.



Forgot to attach an after cleaning pic of the big tube...



I sat down for a little this morning and mapped out the RGB and blanking circuits on the board and labeled them...





Theres a couple spots with jumpers that would be good spots to splice into the lines for the rgb switch method.
Im just clueless what to do from here as the jungle expects .5vpp signal and no clue how to attenuate to those levels.

Ive seen one old post from 2007 on another forum where someone rgb modded this set but was using arcade boards as rgb source and I believe those usually have .5vpp signals.

Also seen people mention pin 43 for sync on this jungle but also seen pin 39 mentioned for these TA1242N's.
Any suggestions if this setup is muxable or should I just move forward with the splice/switch method?

[matt]

Don't do a switch mod. It's more work than the Mux and the results aren't as good.

"M" usually denotes a monitor grade tube such as you'd find in a computer monitor or PVM. Generally they're supposed to have a finer pitch than a TV tube. But apparently some companies did put an M label on consumer TV tubes as well for some reason.

Arcade boards usually output ~3vpp RGB. It has to be attenuated significantly if you want to use it with a TV.

[MarkOZLAD]

Just relax, I'll help you mod it OSD mux style. I'm a busy man and will get to it when I can.

Thanks to Tim Worthington (etim) we have a pattern for 0.5Vp-p attenuation that maintains 75 ohm termination. It looks like this:



In my signature you can see a 0.5Vp-p table for the OSD mux resistor calculations.

You'll need to buy some 24 ohm and 51 ohm resistors.

We will likely use the jumpers you have found to solder the external RGB lines.

[deezdrama]

Just relax, I'll help you mod it OSD mux style. I'm a busy man and will get to it when I can.

Thanks to Tim Worthington (etim) we have a pattern for 0.5Vp-p attenuation that maintains 75 ohm termination. It looks like this:



In my signature you can see a 0.5Vp-p table for the OSD mux resistor calculations.

You'll need to buy some 24 ohm and 51 ohm resistors.

We will likely use the jumpers you have found to solder the external RGB lines.

Awesome, I appreciate it!
Ill start working on this panasonic ag560 that wont power up in the meantime.
I went ahead and recapped full power and deflection side of the board, Had the right values on hand, well except for one cap but its esr tested decent enough.




I have 22 and 47 ohm resistors on hand.... will those be close enough?

[MarkOZLAD]

I have 22 and 47 ohm resistors on hand.... will those be close enough?

They might be ok, better to get the real deal but if you cannot wait....

[deezdrama]

I have 22 and 47 ohm resistors on hand.... will those be close enough?

They might be ok, better to get the real deal but if you cannot wait....

If it will work out better I will go ahead and order them,1/4 watters good enough I assume?
Any other supplies you forsee me needing? I think ill use an old shielded vga cable this time for wiring lol.

[MarkOZLAD]

I have 22 and 47 ohm resistors on hand.... will those be close enough?

They might be ok, better to get the real deal but if you cannot wait....

If it will work out better I will go ahead and order them,1/4 watters good enough I assume?
Any other supplies you forsee me needing? I think ill use an old shielded vga cable this time for wiring lol.

1/4 Watt is fine

Get some 270 ohm and 330R ohm resistors while you're ordering.

[MarkOZLAD]

And some 620 ohm and 1.8K ohm

[deezdrama]

Get some 270 ohm and 330R ohm resistors while you're ordering.

I have plenty of those values

no 1.8k though


Ordered another kit...this one has 130 dif values

[MarkOZLAD]

Get some 104 ceramic capacitors. (0.1uF)

[deezdrama]

Get some 104 ceramic capacitors. (0.1uF)

Ordered...... Now I need to decide on if I will run scart or bnc again.

I will mainly use my mister fpga which uses vga to bnc right now and all of my rgb monitors use bnc, but maybe it would be nice to do a proper scart connection on this one.
All of my consoles that can do rgb use hdretrovision YPbPr transcoder cables but might be nice to have the scart option on this large crt.
I had planned to run my mister through several pvm's and a 20" broadcast monitor and this 36" would be the last display in the chain so would need a bnc to scart adapter.
Since ive never messed with scart im worried ill buy the wrong adapter cable, anything specific I should look for?

Or do you think I should do bnc again to keep it simple?

[matt]

Personally, I put SCART sockets on all my modded TVs nowadays, although generally I'm of the opinion that it's a silly connector design and I don't use it for much else.

My rationale is that it's the only connector that was originally intended for RGB overlays on a consumer TV set. As such, the standard is meant to only use composite video or 75 ohm Csync. By using SCART, there's little chance that a future owner of one of my TVs will buy an off the shelf cable and ruin the jungle chip by plugging in TTL level Csync straight from a computer or a MiSTer.

[MarkOZLAD]

RGB Mod instructions:

EDIT: Revised 1.0Vp-p diagram after deezdrama had tried 0.5Vp-p and failed.




For 1.0V p-p we need a 180 ohm termination resistor to maintain 1.0Vp-p RGB coming in.

(I won't bore you too much with the maths right now but it's basically something like 0.7 * 255/180 = 0.99... The RGB signal from the console is typically sent through a 75 ohm inline resistor.)

For the mux resistor we will cheat by subtracting 180 from the value of the factory grounding resistor (now removed) which was 680 ohm. This leaves as at 500 ohm, nearest standard resistor is 510 Ohm.

This makes the match of the OSD signal 5V * 690/3390 = 1.02V basically same as factory

Spoiler

0.5Vp-p????

The datasheet for the TA1242N suggests 0.5Vp-p RGB input but I cannot be sure. Unfortunately the datasheet is in Chinese and being Australian my Chinese is quite poor....

I've also read in the TV RGB Mod thread that it is 0.5Vp-p but I don't know exactly why they are saying that.

Let's examine the factory OSD circuitry. IC701 MN1874876JZX1 has 5V as it's Vdd. Thus I assume it's a 5V chip and will output 5V OSD. There factory voltage dividers on the OSD RGB uses a 2.7K ohm inline and 680 ohm to ground.

5V * 680 / (2700 + 680) = 1V (1.0059V)

I'm pretty sure I've seen other users that suggest it requires 1Vp-p....

I'm confused but let us first mod for 0.5Vp-p as a test and see how it goes. If it's no good we can revise.

OSD Mux Resistor Calculation

Let's cheat here. The existing OSD grounding resistor is 680 ohm. Because we are using the 0.5Vp-p pattern for termination we will have a termination resistor of 51 ohm. 680 - 51 = 629 ohm. A 620 ohm mux resistor shoud be close enough.

This would result in an OSD voltage of..

5V * (620 + 51) / (2700 + (620 + 51)) = 1V (0.99525V close enough to 1V for my liking)

If it's good enough for the factory it's good enough for me

Physical Mod
Ok, here we go

1) Remove SMD resistors R717, R719, R721 (factory OSD "grounding" resistors)
2) For blanking we want to go from a 5V source into a switch then into a 1.8K resistor and then onto jumper W019
3) For each of the RGB lines we want to bring the external RGB into a 24 ohm resistor and then 51 ohm to ground. Then for each run a line from between these two resistors onto the RGB jumpers into a 620 ohm resistor then onto their respective jumpers.
4) Replace caps C801, 802 and 803 with 0.1uF (104) ceramic caps

Physical Mod
Ok, here we go

1) Remove SMD resistors R717, R719, R721 (factory OSD "grounding" resistors)
2) For blanking we want to go from a 5V source into a switch then into a 1.8K resistor and then onto jumper W019
3) For each of the RGB lines we want to bring in the external RGB, we want 180 ohm to ground. Then for each run a line from between these two resistors onto the RGB jumpers into a 510 ohm resistor then onto their respective jumpers.
4) Replace caps C801, 802 and 803 with 0.1uF (104) ceramic caps

[deezdrama]

Wow dude that was quick. Wish I could buy you a beer lol.
I have a funeral to go to tomorrow but plan on jumping on this soon after.
Awesome work... I appreciate it!

[deezdrama]

This chassis board was laid out much easier than that phillips for the mod. I didnt have to run a wire over 6 inches.
That back panel input plate was such a convenient spot to mount connectors that I just had to use it.
Hopefully there will be no interference from the raw ac line coming in near where I put the bnc connections?

I used these large buttons because they were left over from a mister fpga case project.














All I have left is to run the ground to a ground header pin I put right below the bnc connectors and solder the rgb lines to the jumpers on the board but im kind of at an ocd induced standstill.....
Lol.... I replaced all caps on power-deflection half of the board but one, i didnt have a 2200uF 25v+ on hand.
This triggered my ocd even though it tested decent I ordered a couple caps of this value.
So I want to button the job up and test but kind of just want to wait untill that cap is replaced, i guess I can finish and just pull the board again when the caps come.

So... My only question now is in reguards to sync.... Ive seen mention of pulling sync from pin 39 or pin 43.... Could i not pull sync on the rear composite input again?

[MarkOZLAD]

Sync into factory AV port (composite or svideo luma, even component Y)

This is the way.

[deezdrama]

Sync into factory AV port (composite or svideo luma, even component Y)

This is the way.

Another good job Mark!
Im going to owe you alotof beers now lol.

This tube really blew me away! Geometry and convergence are damn good on this one!

Menu picture settings wont affect rgb image since its injected last but I knew this going in, I guess I need to adjust it with the g2 voltage and sub brightness in service menu.
Ill save that fun for tomorrow night.
Cant wait to play on this monster!

Thanks again!

[MarkOZLAD]

Looks good. Glad the theory worked in practice.

[kitty666cats]

Nothin’ like a ginormous slot mask! Arcade-ey bliss.

[deezdrama]

Nothin’ like a ginormous slot mask! Arcade-ey bliss.

Definitely, I hope I can get brightness/contrast tuned in.... Will be an awesome tube to use Mister on!

[deezdrama]

Looks good. Glad the theory worked in practice.

So I turned down the g2 pot to get brightness set right and now its not washed out and black levels are nice but overall still very dim.



Ive tried adjusting basically everything possible in the service menu and none of it has an affect on the rgb image. I just need some more contrast/picture.

Any clues or ideas? Maybe something needs toggled in the service menu for some other adjustments to take affect?


Heres what Im working with...

[MarkOZLAD]

Sounds like you might have to go straight to the RGB drive and cutoff settings.

A good idea to write down the factory defaults before you do.

Use the 240p suite’s colour bars pattern.

[deezdrama]

Sounds like you might have to go straight to the RGB drive and cutoff settings.

A good idea to write down the factory defaults before you do.

Use the 240p suite’s colour bars pattern.

I think I fried something (crying on floor lol)

I had cutoffs down and went to turn up g2 .... Being such a big ass tube I couldnt see the screen so decided to turn the knob about 2mm of travel which I guess was too much.

TV shut itself off. When I turned back on I got flashing red light.
Had to unplug for a min and now I get the rgb image but its out of sync so the blue screen this jvc has when no signal is detected is superimposed onto the rgb signal and out of sync and rolling.

Ugggg. This sucks

[deezdrama]

After giving up and unplugging the tv for about 30 min, I un-gave up and tried it again with a composite signal....It worked but menu was funky colored like a rgb blank that isnt fully blanked, I had to turn up g2 a hair to get normal conditions....Everything back to normal with composite.


Plugged the mister back in and its working (yessssssss!)

Can anyone explain on an electrical basis what happened here? I know I overvolted it and probably kicked in a protection.... did I just need to give it time to reset or did I likely overheat some components?

Anyway.... Ive found 3 sections with rgb cutoff... "low light" "high light" and "theatre" categories.

Low and high are not display options like "standard, choice, and theatre" ....
I can have g2 up and correct black levels by lowering rgb cutoffs in the "high light" and "low light" menus but once I back out of those categories the cutoff settings are not applied anymore.
Cant really tell if they are applied to theatre mode or not because its so dim and crappy looking from the start.

This isnt going to be easy or fun to get to look good

I mean I can tell its a sweet tube and has potential .... I just need black levels blacker



EDIT.... The rgb levels under the low light and high light white balance settings do apply to overall image. I just had to turn them up way higher than I thought they would go initially and had to read the service manual to figure out the rgb levels could only be set by using the numbers on the remote which took me a while to figure out since all other service menu settings are done with the arrows