Hitachi 27" 27MM20B Dual-Scan CRT TV??

[Syntax]

Diodes are just there for isolation.
You can use some to ground on the incoming rgb lines for extra safety also. All depends on how much you care really.

I'll take a look at the service manual tonight and draw something up for you.

[Josh128]

Thank you! That would be awesome! The SM posted earlier in the thread should show you what you need, if you need any specifics I can answer, just let me know.

[SuperSpongo]

I would use the monitor in the worst condition for the first RGB mod, just in case

[Josh128]

I would use the monitor in the worst condition for the first RGB mod, just in case

Yep, definitely! I was looking at doing this one, but I got cold feet once I plugged the jungle daughter board back in and the TV refused to power up. Turns out the board wasnt completely seated, but I got it going, lol. Syntax is going to help me with this. Honestly Im so pressed for spare time I dont know where to turn right now. I have none. I had to cook supper for the family last night while my wife ran the kids about until 7:00PM. I had this unit apart to get the pics and check things out and time was running out quick and I was getting bad vibes lol. I had to close it up and start cooking, lol.

Im planning to use a female SCART as I have several of them, along with some wire robbed from a VGA cable.

[maxtherabbit]

Im planning to use a female SCART as I have several of them, along with some wire robbed from a VGA cable.

super gross, you should be able to just wire it to the existing VGA port on the TV

[SuperSpongo]

I vote for Scart

But seriously, if you want to sell these, Scart would be a selling point for most.

[maxtherabbit]

I vote for Scart

But seriously, if you want to sell these, Scart would be a selling point for most.

1) wrong (fuck scart all my homies hate scart)

2) Think about what you're saying. Port type aside, do you really think that having to use different RGB inputs for different resolutions is going to be a selling point? Most people with multi source switcher setups don't segregate 15 and 31kHz sources, they all share the same path

[SuperSpongo]

I'm not gonna be the one to fan your burning passionate hate flames for Scart lol

Sure, keep it VGA only, what do I care. I'm convinced!

[mrsmiley381]

So what's the strategy for managing 15/31kHz signals on the same port? Reading through the thread it didn't seem like there was an easy way to manage resolution switching from 480i to 480p easily. That or I misunderstood how the intended RGB mod works.
I'm really trying to think of how many 384p games I'll ever play. Maybe I should order three of these from you and call it a day. Good thing my wife appreciates a good tube.

[SuperSpongo]

If they're going the OSD route, you will have to set the monitor to 15kHz mode (as opposed to the PC mode Josh mentioned in point 2) and activate a blanking voltage with a switch, if I remember correctly.

[maxtherabbit]

So what's the strategy for managing 15/31kHz signals on the same port? Reading through the thread it didn't seem like there was an easy way to manage resolution switching from 480i to 480p easily. That or I misunderstood how the intended RGB mod works.
I'm really trying to think of how many 384p games I'll ever play. Maybe I should order three of these from you and call it a day. Good thing my wife appreciates a good tube.

my proposal would still keep the processing paths inside the television separate (for the most part) but simply pull the signals from the same connector to make it less onerous to the end user

(so you'd only have to switch modes on the TV, not hook up a separate cable)

[tongshadow]

So what's the strategy for managing 15/31kHz signals on the same port? Reading through the thread it didn't seem like there was an easy way to manage resolution switching from 480i to 480p easily. That or I misunderstood how the intended RGB mod works.
I'm really trying to think of how many 384p games I'll ever play. Maybe I should order three of these from you and call it a day. Good thing my wife appreciates a good tube.

Pretty simple, we can wire the DB-15 pins into whatever pins the RGB input goes into and use a switch to change between 15kHz and 31kHz. The switch could be installed easily if we remove that 7 pin PC input or just remove the RF input.

Clean, no butchering required, and 100% reversible.

[Josh128]

Im planning to use a female SCART as I have several of them, along with some wire robbed from a VGA cable.

super gross, you should be able to just wire it to the existing VGA port on the TV

lol, I really would actually like to do that, but the problem with sharing the VGA port means any individual signal I feed (15KHz or 31KHz) will then be terminated at two different inputs on the jungle card, which will drop the signal at either point by 3dB and also perhaps create more likelyhood of reflections. Only way around that would be to feed a 4PDT switch so only one input would be terminated at a time and thus not draw down the signal of the connected source. If you have another idea about how to prevent that, let me know.

[Josh128]

Also, whats your guys take on those inputs (15kHz) and (31kHz) on that jungle chip diagram? Does anyone know if it would be possible to "force" the TV into 15KHz mode or 31KHz mode by pulling low or high those inputs? All while having the actual TV in PC mode? Boy that would be damn awesome if it worked like that. All you would need is a switch on the back to change modes, no other wiring needed. You could potentially feed the existing port with 15kHz and it would work. (Might need a sync splitter though maybe to split the Csync into individual H/V?)

[tongshadow]

This might be even more simple than I thought, see where that 15kHz trace goes. Like blanking, it might just be a matter of switching between the 2 modes using a simple switch. I dont think OSD gimmicks will be needed here.

[Josh128]

This might be even more simple than I thought, see where that 15kHz trace goes. Like blanking, it might just be a matter of switching between the 2 modes using a simple switch. I dont think OSD gimmicks will be needed here.

It goes to the output of a transistor just like the 31kHz trace.
If those are indeed inputs and not outputs. They are on the output side of a transistor though, so I assume they are inputs. That would be something. If anyone knowledgable about this IC knows, please chime in.

[kitty666cats]

If the VGA port is gonna end up needing a physical switch for going between 15/31kHz modes, at that point you might as well put 15kHz on the composite input (w/ a switch if you feel like using a composite source), that way you can switch between 15 + 31kHz sources with the remote. For content that switches between 15/31kHz, you could use a splitter/distribution amplifier and send it to both RGB inputs + switch w/ remote as needed.

If you were to do this, either a VGA connector (or 4 BNC/4 RCA) would probably be ideal as powered VGA splitters are super cheap. SCART is fine too, so silly to get so heated over a AV connector (I use VGA-style cables, personally, but there is so much SCART gear being made that it’s a totally valid option)

[maxtherabbit]

Im planning to use a female SCART as I have several of them, along with some wire robbed from a VGA cable.

super gross, you should be able to just wire it to the existing VGA port on the TV

lol, I really would actually like to do that, but the problem with sharing the VGA port means any individual signal I feed (15KHz or 31KHz) will then be terminated at two different inputs on the jungle card, which will drop the signal at either point by 3dB and also perhaps create more likelyhood of reflections. Only way around that would be to feed a 4PDT switch so only one input would be terminated at a time and thus not draw down the signal of the connected source. If you have another idea about how to prevent that, let me know.

use a buffer IC

[Syntax]

They are both high when in TV mode, and Low when in PC mode.

The table to the left indicates that.

I'm more interested in the pins 10 33 35, they shift between solid 5v high and low depending on video mode.

11 might be a sneaky little switch also.

[maxtherabbit]

honestly depending on how the factory RGB input is terminated you might just be able to tap it right after the existing 75R termination and inject that signal into your OSD input

the jungle IC is going to be extremely high-z terminated internally so it won't bring down the levels, and the OSD outputs are mutually exclusive depending on set mode, just use the diodes

[maxtherabbit]

They are both high when in TV mode, and Low when in PC mode.

The table to the left indicates that.

I'm more interested in the pins 10 33 35, they shift between solid 5v high and low depending on video mode.

11 might be a sneaky little switch also.

I really hope this approach works, my concern with that was the IC that handles RGB clamping in PC-mode is controlled by i2c

[Josh128]

They are both high when in TV mode, and Low when in PC mode.

The table to the left indicates that.

I'm more interested in the pins 10 33 35, they shift between solid 5v high and low depending on video mode.

11 might be a sneaky little switch also.

Yeah, there are 4 different video modes on this set, RF, CV, SVID, and PC. I was wondering how that works-- say, TV/PC1 goes high for CV, TV/PC2 goes high for SVID, and TV/PC3 goes high for PC. Each time you hit the input button it cycles through them maybe? What were you thinking?

It would be curious to have the set in PC mode and then apply different signals to the 15/31kHz pins to see what would happen.

jortego128@centurylink.net

[Syntax]

Could see what happens when sending csync to luma or composite while also having a 15k signal on vga

[maxtherabbit]

Could see what happens when sending csync to luma or composite while also having a 15k signal on vga

Based on my reading of the service manual there are separate RGB switching ICs and h-drive generation paths. If you are pulling sync from the TV-input the RGB switch will only display the signal from the jungle IC, and vice versa

[Syntax]

OSD mux to the VGA port then with diodes and blanking off pin 9.

[maxtherabbit]

OSD mux to the VGA port then with diodes and blanking off pin 9.

yeah I think that's probably best, but of course haven't been hands on with one yet

[Josh128]

Got a few shipped out so far, waiting for confirmation that they made it OK. Theres actually a decent demand for these. Folks that would like one, please be patient as I literally have very little time to test pack and ship lately, but Im working on it.

My email is jortego128@centurylink.net.

[loopyeddie]

Are these monitors ok? The hurricane didn’t get them, did it?

[Josh128]

lol they are OK, where I (and they) are located, Evangeline Parish, LA we dodged a bullet and the storm totally missed my area.
We got some gusty breeze, thats it. Eastern Louisiana, however, got some catastrophic damage. Most of New Orleans may be without power for weeks.

I was mistaken about the other monitor I shipped the same day as yours being at destination, I got a notification today it was still in transit in Missouri. Yours should definitely arrive at the destination terminal by Thursday or Friday this week, I believe.

[loopyeddie]

Awesome, I am very pumped!