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

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Syntax
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Re: Hitachi 27" 27MM20B Dual-Scan CRT TV??

Post by Syntax »

IMO its better to just add a switch to the set for blanking.

Theres always so many issues with different setups not supplying voltage correctly.

EG: If you go from an Extron VGA splitter then you have no voltage supply for blanking.

GScart supplies a solid voltage no resistor divider network, and its lower than some sets need to blank, so your network has to accommodate for that.

Every set that I have RGB modded for auto blanking I went back and added a switch that drew from an internal power source.
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Josh128
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Re: Hitachi 27" 27MM20B Dual-Scan CRT TV??

Post by Josh128 »

So blanking (or lack of/ not enough blanking voltage) is whats causing this then. Hmm, I'll have to revisit it.
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Josh128
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Re: Hitachi 27" 27MM20B Dual-Scan CRT TV??

Post by Josh128 »

Got some rudimentary RGB working. Had to completely remove the resistors on the blanking line, went straight wire. The image is about 1/2 as bright as using the Genesis w/ GBS-C going 31KHz into the VGA ports though. I think I may h have to reduce or remove the RGB inline resistors.

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Josh128
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Re: Hitachi 27" 27MM20B Dual-Scan CRT TV??

Post by Josh128 »

Got some better shots of 15kHz RGB. Played with different resistor configs, but could never get it as bright and colorful as the VGA in. I suspect its because my lines are connected with the existing OSD lines. I bet if I used a QPDT switch to isolate the OSD and RGB in from each other, it would resolve that issue.

Below is a gallery of some photos of my Genesis 2 running direct RGB into the set.

https://imgur.com/a/gAV5pAb

jortego128@centurylink.net
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Syntax
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Re: Hitachi 27" 27MM20B Dual-Scan CRT TV??

Post by Syntax »

Muxing is pretty straight forward, but if the whole process is a bit confusing to follow id just wait for @Maxtherabbit to mod his sets and copy him.
Should be an easy clean mod
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Josh128
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Re: Hitachi 27" 27MM20B Dual-Scan CRT TV??

Post by Josh128 »

Syntax wrote:Muxing is pretty straight forward, but if the whole process is a bit confusing to follow id just wait for @Maxtherabbit to mod his sets and copy him.
Should be an easy clean mod
I understand the mux method and it does seem pretty straightforward, but the things that complicate the installation for me are:

1.) Each OSD output line from the microcontroller parallels to ground with a 100pF cap, is then series connected to a 220R then a 3.3kR resistor, meanwhile the 220R and 3.3kR form a voltage divider feeding a line to OSD2 (VGA OSD). That line hits a 180p cap paralleled with a 4.7kR resistor before heading off to OSD2 switch. The 3.3kR resistor on the line to OSD1 is paralleled with an 18pF (if thats not a mistake on the schematic) cap then is paralleled to a 2.7kR grounding resistor before heading of to OSD1. This makes it pretty damned complicated to figure out if Im supposed to just use a 2.7kR grounding resistor on my blanking line or if it should be something else.

2.) I was not able to locate the R01R 2.7k blanking line grounding resistor on the PCB. I may need to look again, but I'll be damned if I didnt spend an hour looking with a magnifying glass and a DMM at both sides of the main PCB but couldnt find it, at least the way its shown in this diagram. So I couldnt remove it. I went ahead and used a 2.7k inline res on my console blanking line along with a 75R grounding res at first, but it gave me the "game in OSD text & graphics" issue. I then removed both resistors off the blanking line and that worked.

3.) The RGB lines are setup similarly to the Blanking line, except they dont have a grounding resistor at all. So I really dont know what value to use to calculate my inline resistors for my console RGB lines. I initially just went off of the 4.7kR resistor value which gave me 750R to use on my lines. Maybe I should use the total of OSD1 and OSD2 ladders -- 220R + X when 1/X= (1/4.7kR +1/4.7kR) while ignoring the grounding and parallel caps when calculating my resistor values? IDK man, seems pretty complicated. :lol:

EDIT: I also forgot to mention Im using an Insurrection Industries Genesis 2 SCART cable, which claims its wired for dedicated csync. Im not sure what they mean with that, because the Genesis 2 only outputs composite video, and on pin 20. Ive wired that direct to Y(S) in on the jungle chip (pin 39), which is supposed to be composite video in. Strangely enough, I dont get sync when Video input is selected, I must use the S-Video input to get sync--- and usually then it starts out wavy then syncs up after a couple seconds. There are a couple other pins that could be used for video in, perhaps I should try one of those to see what happens.

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bobrocks95
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Re: Hitachi 27" 27MM20B Dual-Scan CRT TV??

Post by bobrocks95 »

Genesis 2 outputs csync on pin 5 of this diagram
Spoiler
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Josh128
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Re: Hitachi 27" 27MM20B Dual-Scan CRT TV??

Post by Josh128 »

Hey Bob, I can't read your diagram, can you blow it up a bit please? :mrgreen:

Seriously I wasn't aware of that, the pinout I was looking at didn't show it. Maybe that has something to do with the sync taking the time it does. Need to look at the levels.
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bobrocks95
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Re: Hitachi 27" 27MM20B Dual-Scan CRT TV??

Post by bobrocks95 »

lmao sorry I posted it on mobile and it looked okay haha. Most of the typical pinout diagrams you see really didn't want me to embed the links as images either, they kept failing to load. But yeah, typical TTL CSync is available.

You might have seen one of the diagrams on this page from Tim that note CSync in the pinouts but not shown on the diagrams http://members.optusnet.com.au/eviltim/ ... escart.htm
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Josh128
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Re: Hitachi 27" 27MM20B Dual-Scan CRT TV??

Post by Josh128 »

Yep, thats what I was looking at. Ok, I need to verify whether my cable is sending Csync or CVideo to SCART 20.
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Josh128
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Re: Hitachi 27" 27MM20B Dual-Scan CRT TV??

Post by Josh128 »

Spreading these throughout the land. :mrgreen: Just got this from one of the buyers I shipped two sets to last Thursday, what a great photo!


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

Post by SuperSpongo »

Very nice!
So was his RGB mod successful or is this a pic of linedoubled with fake scanlines? I'm guessing the former, seeing how bright the image is.
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Josh128
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Re: Hitachi 27" 27MM20B Dual-Scan CRT TV??

Post by Josh128 »

He just picked it up yesterday, so Im almost certain this is line doubled + scanlines either from a scaler or a PC. I'll ask him. To your point though, the image is actually very bright when using my GBS-C + Genesis with scanlines. Looks no dimmer than GC @ 480p. Dont ask me how that is, but you will not be wanting for brightness even if line doubling + scanlines. Its damned good looking when used in that mode.

And as I posted a few posts back with my first attempt at an RGB mod, the 640x480 mode with GBS-C + scanlines was twice as bright as my native 15kHz mod. I had to retreat from that battle, but I will return to the battle and tinker some more till I get it right, because it did look pretty much perfect except for the brightness. It would actually be plenty acceptable for a dark or even semi-dark room as it was, but I know it should be brighter.
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strayan
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Re: Hitachi 27" 27MM20B Dual-Scan CRT TV??

Post by strayan »

You’ve also got a pretty good opportunity to do some blind tests to see if you can tell the difference between s-video and rgb :mrgreen:
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Josh128
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Re: Hitachi 27" 27MM20B Dual-Scan CRT TV??

Post by Josh128 »

strayan wrote:You’ve also got a pretty good opportunity to do some blind tests to see if you can tell the difference between s-video and rgb :mrgreen:
Oh crap, I hadnt considered that-- this could very well be an S-video feed. Do you know something we dont? :lol:
Climhazard
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Re: Hitachi 27" 27MM20B Dual-Scan CRT TV??

Post by Climhazard »

Josh128 wrote:
strayan wrote:You’ve also got a pretty good opportunity to do some blind tests to see if you can tell the difference between s-video and rgb :mrgreen:
Oh crap, I hadnt considered that-- this could very well be an S-video feed. Do you know something we dont? :lol:
Hey Josh, I'm the guy you sold those 2 sets to.
That is indeed just straight s-video from the SNES. Both sets look great!
I've had a chance to do some more testing this morning and I have noticed one issue with the s-video input. Whenever there is a bright flash on screen or a game goes suddenly from a dark screen to a very bright screen the whole screen will flicker, almost like the TV is losing sync for just a fraction of a second.
Here's a short video example.
https://imgur.com/a/prNH9nw
I've tested SNES, PS1, and Sega Saturn so far and it's happened on all of them so it's not a console issue. It also only happens on the s-video input, composite works perfectly fine. I don't currently have anything on hand to test out the VGA input.
I'll try to open her up once I have more time this weekend and look for anything loose but if anyone has a more specific idea on what to look for I would appreciate it. I'm far from an expert on CRTs, especially consumer sets, my experience is limited to doing a few recaps and manual deflection adjustments on some older arcade monitors.
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Josh128
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Re: Hitachi 27" 27MM20B Dual-Scan CRT TV??

Post by Josh128 »

Quick update. I Wanted to show what these look like packed ready for delivery to terminal.

Large pallet on the back contains 3, smaller pallet contains 2. There is some overhang on a standard 40"x48" pallet when shipping 3, and will certainly be if shipping 4. Ive been telling buyers that want more than two on a pallet that there is increased risk of damage when there is overhang. Its just the nature of freight and is a known quantity.


Although there has been no monitors that Ive shipped that we have not been able to get working, I have removed the freight option from my Ebay, which is now local pickup only. Purchases requiring shipment must be done directly, and I am making it very clear that while I test the units and now reflow known problem areas that have given issues in past shipments prior to packing and shipping them, once they leave my truck I can offer only support and suggestions should a unit arrive DOA. The freight carrier I use offers a guarantee against lost and/or physical damage to the package, which includes the cost of the freight + around $300 for the item. That however does not include a shipment which looks to be fine physically, but has a unit that no longer works / has internal non outwardly visible damage. I email instructions to buyers on how to properly receive freight, issues/damage MUST be noted on the paperwork you sign upon acceptance.

My email is jortego128@centurylink.net

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yatzr
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Re: Hitachi 27" 27MM20B Dual-Scan CRT TV??

Post by yatzr »

Has anyone figured out how to use the hidden menu to adjust geometry in tv mode? I hold the input button while powering up, like the service manual says. I expect A00/000 to show up, but instead P00/000 shows up and my cursor buttons don't do anything. Not sure if I'm just being dense about it.

Also wanted to share a couple nice things I've learned about these monitors:
They can sit on their side pretty well. Not as sturdy as a pvm, and I wouldn't trust children around it, but it's not gonna fall over on its own either. I've been playing a bunch of tate games on it, and it's great!
They turn on automatically if you just pull power and give power! That, along with how it remembers what input you were on makes them surprisingly suitable for arcade cabinets. If I had plans to build a cabinet, or if I get desperate for a replacement in one of my candy cabs, these are a strong contender. The one I've been using looks better than the monitor I have in my vert blast city, and that makes me go hmmmm :lol:
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Josh128
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Re: Hitachi 27" 27MM20B Dual-Scan CRT TV??

Post by Josh128 »

yatzr - you must use the up/down directional arrows on the remote to scroll through the codes and left and right arrows to adjust the values. It has to be done on the remote, which is strange, because you cant enter the service menu with the remote.

Yeah, I have a WG K7000 in my Mace cab, and I bought a 27" Wei-ya tri scan (which I fried) for it cause I wanted that delightful 25kHz. Now I have these and I would love to see how they respond to a 25KHz signal. Ive run across an interesting problem on one of them-- it doesnt sync up in VGA mode, ie the floating text doesnt go away ,but it still displays a darkened image of what you feed it. If you feed it 15kHz, well, you can see it perfectly, in 15kHz mode! Makes me wonder if theres not a way to mod these to run in 15kHz mode when on the VGA input. I bet there is.
yatzr
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Re: Hitachi 27" 27MM20B Dual-Scan CRT TV??

Post by yatzr »

Interesting! The manual says you can use either. loopyeddie, I am gonna need one of those remotes after all :lol:

I was reading through the manual and there's a few things that seem promising. On I001, there's three different pins that all control different aspects of switching between tv mode and pc mode. TV/PC1 is for choosing which sync to use, TV/PC2 is for choosing which RGB and audio to use. Don't know what TV/PC3 is actually for. That might tell other parts which OSD to use. I need to trace these through the schematic to see where all they go. I kinda wonder if you can tell it to use PC sync and PC rgb/audio while also telling it to use tv mode. It'll probably be a couple weeks before I have time to try it out, but if nobody else has by then, I'll give it a go.
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Josh128
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Re: Hitachi 27" 27MM20B Dual-Scan CRT TV??

Post by Josh128 »

Yeah it does, but unless you need to hold some combination of buttons that it doesnt mention, you cant navigate with the TV buttons.

Also, if thats the unit I labeled as #2 you are using, that unit from what I remember is probably the best convergence and geometry set I've tested so far. Its top-tier. Im not surprised it looks better than the monitor in your BC cab. Im currently playing with the bad boy below, the crown jewel of the load (of the Hitachi's anyway, I havent yet tried one of the 4 Zeniths I have) the 27MMV30B, the next iteration of the set you have. The only difference Ive seen so far from the previous year models are the "bold new silkscreen graphics" :lol: , NO bodges on the main PCB (nice to see they were continually improving the design), and the PA2 DDC satellite board. All that said, the convergence on your #2 20B set is still better than this one, lol. :mrgreen:

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maxtherabbit
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Re: Hitachi 27" 27MM20B Dual-Scan CRT TV??

Post by maxtherabbit »

man I can't wait to get my hands on one of these!
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Josh128
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Re: Hitachi 27" 27MM20B Dual-Scan CRT TV??

Post by Josh128 »

Finally connected a DC to the set shown above. Pretty nice picture. As I mentioned earlier, reminds me a lot of the Wei-ya M-3129.

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yatzr
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Re: Hitachi 27" 27MM20B Dual-Scan CRT TV??

Post by yatzr »

I spent some more time digging through the schematics. Someone more familiar with chassis schematics should check me on this, but it looks like TV/PC3 (pin 10 of I001) controls the crt mechanics, like it's what tells it to run in 31kHz or 15kHz. I001 will output 5V for pc mode which will trigger 31kHz, and 0V for tv mode which will trigger 15kHz. This output also goes through a resistor right away, so it'd be pretty easy to pull that up and hijack that line. I haven't looked at the chassis again yet, but there's also a really good chance there's a jumper in the line somewhere too, and that might be even easier to pull up and hijack. I think it'd be worth a test to set this line to 0V while the monitor is in pc mode to see if that triggers it to switch back 15kHz (making sure to break the connection to I001 so as not to short it out of course). If it does, then send some 15kHz video through and see what happens. It's not clear to me if the sync detect will still complain and darken the screen.

Another option, which seems a little more likely to work to me is to leave TV/PC3 alone, but hijack the lines for TV/PC1 and TV/PC2 (I001 pins 35 and 33 respectively). Again, I001 will output either 0V or 5V. For some reason these are opposite of each other though. TV/PC1 is 0V for tv mode and 5V for pc mode while TV/PC2 is 5V for tv mode and 0V for pc mode. They also go through resistors right away. It looks like these only control switches for which HVsync and RGB/audio lines get sent to the crt. So I think it'd be worth a test of having the monitor on one of the tv mode channels, sending 15kHz through the vga, and then toggling these two lines.

My gut says the second option is more likely to work, but if the first one does, then I could envision an auto sync mod where you try to detect if vga is getting 15kHz or 31kHz and set the TV/PC3 line appropriately. I've got a different big crt opened and taking up my workspace or I'd test these out right now. I may be able to try it next weekend.
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Josh128
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Re: Hitachi 27" 27MM20B Dual-Scan CRT TV??

Post by Josh128 »

This is what Ive been thinking as well. I'd like to try various combinations of this to see what, if anything, will work. The VGA port video lines go through the sound pcb, then I551, then I552, which is a switch. That might throw a wrench into option #2. I think the 15kHz/31kHz pins on I001 tell is which OSD to output, VGA or the normal TV one.
yatzr
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Re: Hitachi 27" 27MM20B Dual-Scan CRT TV??

Post by yatzr »

From the service manual
"The (pc) RGB signals are amplified and output at from I551 pins 25, 30 and 35 respectively to the I552 RGB switch, where it is switched between the TV RGB and input to the Video output circuit"
TV/PC2 gets fed into I552 on pins 9, 10, and 11 through a couple transistors to perform the switch. Option #2 still makes a lot of sense to me.

I don't think the 15kHz and 31kHz pins on I001 control anything. They are both inputs. The 31kHz line is connected to the vga hsync pin through a transistor, so it'd always be going anytime you're feeding video through the vga port. I think they get used internally for something in that chip when the input has been switched.
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Josh128
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Re: Hitachi 27" 27MM20B Dual-Scan CRT TV??

Post by Josh128 »

Since OSD 1 and OSD 2 both come from the same pins on the microcontroller, some input has to tell I001 which type of OSD to output. My guess is that that is what the 15kHz and 31kHz pins do. They must do something otherwise they should just be pulled low/grounded. Could be something else though.

As you said, TV/PC2 output looks like it is switches the RGB SW to output either TV RGB or PC RGB, TV/PC1 output looks like it switches between TV and PC sync, and TV/PC3 looks like it actually switches the mode from TV to PC. What that means is kind of unclear-- maybe it does perform the 15/31kHz circuit switching.

So yeah, option #2 might be worth trying. It may well be possible that switching TV/PC2 and TV/PC1 that a certain combination might allow the set to receive RGB from the VGA port while in 15KHz mode-- If it can use composite sync or composite video on the HSync input to get proper sync. If not, it might be necessary to use a sync splitter to split composite to H/V before inputting to the TV.

In any case, if it becomes morework than astandard RGB mux mod it might not be worth it. One benefit though, is that it would pass through the video amplifier and as long as the input signals are not too hot, the output should be at levels the TV is expecting and you would still have your PC OSD without the need for any added resistors or switches, other than for TV/PC1 and TV/PC2. It will be cool to see how this progresses.
Last edited by Josh128 on Tue Sep 14, 2021 2:32 am, edited 1 time in total.
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Re: Hitachi 27" 27MM20B Dual-Scan CRT TV??

Post by maxtherabbit »

Josh128 wrote: In any case, if it becomes morework than astandard RGB mux mod it might not be worth it.
If it can be done, it would definitely be worth it. You're going to get better clamping and DC restore, and a factory OSD and UX
yatzr
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Re: Hitachi 27" 27MM20B Dual-Scan CRT TV??

Post by yatzr »

I got antsy and had to try this out, so I rigged up option #2 on my backup monitor. There's good news and bad news.

I pulled one end of resistor of R040 and R043 (which go to TV/PC2 and TV/PC1 on I001) and soldered long wires to both the now empty through hole and the end of the resistor. I also soldered long wires to 5V and GND. First I connected the wires together such that it was same as factory, just to confirm everything still worked normal. I plugged a misterfpga into the vga port and an n64 into the composite port. Turned the tv on, and everything worked like normal.

I had the monitor on the composite channel showing the n64, then switched TV/PC2 to be ground, and it worked beautifully to pull in the RGB from the misterfpga! The sync wasn't there, as expected, so the screen was scrolling, but the colors all looked good. That's the good news.
Then I tried switch TV/PC1 to 5V and screen went blank and the monitor made a sound like when you switch inputs between tv and pc mode. That pin seems to control a little more than I thought. That's the bad news.

Anyway, the success of TV/PC2 makes me think you could just make a scart adapter that sends the rgb through a vga connector and a composite sync through an rca plug and get this to work super easy. I gotta see if I have a female scart somewhere to try that. Tonight, I might also try switching TV/PC3 just to see what happens.
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Re: Hitachi 27" 27MM20B Dual-Scan CRT TV??

Post by maxtherabbit »

If getting it to switch sync internally doesn't work out, you could just tap the back of the hsync pin with a suitable resistor and switch, if needed
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