shmups.system11.org

Shmups Forum
 
* FAQ    * Search
 * Register  * Login 
It is currently Sun May 22, 2022 10:32 am View unanswered posts
View active topics



Post new topic Reply to topic  [ 231 posts ]  Go to page Previous  1 ... 4, 5, 6, 7, 8
Author Message
 Post subject: Re: Hitachi 27" 27MM20B Dual-Scan CRT TV??
PostPosted: Sun Dec 05, 2021 6:13 am 


User avatar

Joined: 09 May 2005
Posts: 476
Location: Honolulu, Hawaii
The weird thing about these TVs is that they will sync just fine with composite sync. However, without a signal on the Vsync pin it gives the "connect a PC" error message (even though you can still see a stable image in the background). It works fine with Csync+Vsync, though.


Top
 Offline Profile  
 
 Post subject: Re: Hitachi 27" 27MM20B Dual-Scan CRT TV??
PostPosted: Sun Dec 05, 2021 7:31 am 



Joined: 08 Dec 2011
Posts: 33
So if i wanted to keep my gscartsw and try to keep the unplugging to a minimum. does scart give the same tesolutions vga does? sorry for newbie questions only ever messed with scart.


Top
 Offline Profile  
 
 Post subject: Re: Hitachi 27" 27MM20B Dual-Scan CRT TV??
PostPosted: Sun Dec 05, 2021 9:08 am 



Joined: 19 Mar 2017
Posts: 617
matt wrote:
8bitForLife wrote:
Ill also be using a dreamcast and I have the scart cable from retro access for it but is there anything else ill need?


I'd recommend against using the Retro Access SCART cable. This TV doesn't like composite sync - you'd be better off using a VGA box or cable. A cheap Dreamcast VGA cable would probably work fine.


If he connects a RA Dreamcast SCART cable to a GBS-C AIO then composite Sync is irrelevant since the GBS-C outputs seperate H & V sync.


Top
 Offline Profile  
 
 Post subject: Re: Hitachi 27" 27MM20B Dual-Scan CRT TV??
PostPosted: Sun Dec 05, 2021 9:31 am 


User avatar

Joined: 09 May 2005
Posts: 476
Location: Honolulu, Hawaii
8bitForLife wrote:
So if i wanted to keep my gscartsw and try to keep the unplugging to a minimum. does scart give the same tesolutions vga does? sorry for newbie questions only ever messed with scart.


Usually not. It's supposed to be used for 15khz RGB with composite video for sync, which is quite different from VGA (31khz RGB with TTL level H/V sync). These Hitachis only accept standard VGA in RGB mode, so anything with a SCART connector will require some sort of conversion.

But, what the RA cable does is to run the Dreamcast's H and V sync through a combiner circuit to provide composite sync. This means that it can pass a 31khz signal, but with composite sync instead. This is not a standard configuration, but it's useful if you have something that's compatible with it.

In your case, you should be able to run it through your GSCART/GBS-C combo, which would also let you run 240p-only games like Bangai-O and Gunbird 2 if needed.


Top
 Offline Profile  
 
 Post subject: Re: Hitachi 27" 27MM20B Dual-Scan CRT TV??
PostPosted: Thu Jan 13, 2022 6:03 pm 



Joined: 23 May 2013
Posts: 32
I just recently ran into a weird issue with mine and I'm curious if anybody else has had this happen.

I was testing an nes with composite video on it and everything was fine for 10 minutes, then the video went black. The OSD can still come up fine. I cycled through the inputs and normally I'd get a grey screen on s-video if nothing is connected, but it was also black. Then on the regular tv channel, I normally see "snow" static, but it was also black (can still hear the static though). I panicked and tested my pc input which I normally use exclusively, and everything was fine there. So it appears I've just lost normal video output on all the 15khz channels. The OSD still works fine on all of them.

I did a whole bunch of power cycling, reconnecting things, etc. I couldn't get the video to come back.


Top
 Offline Profile  
 
 Post subject: Re: Hitachi 27" 27MM20B Dual-Scan CRT TV??
PostPosted: Sat Jan 15, 2022 2:06 am 



Joined: 08 Dec 2011
Posts: 33
anyone selling 1


Top
 Offline Profile  
 
 Post subject: Re: Hitachi 27" 27MM20B Dual-Scan CRT TV??
PostPosted: Sat Jan 15, 2022 2:15 am 


User avatar

Joined: 16 Jan 2014
Posts: 1748
yatzr wrote:
I just recently ran into a weird issue with mine and I'm curious if anybody else has had this happen.

I was testing an nes with composite video on it and everything was fine for 10 minutes, then the video went black. The OSD can still come up fine. I cycled through the inputs and normally I'd get a grey screen on s-video if nothing is connected, but it was also black. Then on the regular tv channel, I normally see "snow" static, but it was also black (can still hear the static though). I panicked and tested my pc input which I normally use exclusively, and everything was fine there. So it appears I've just lost normal video output on all the 15khz channels. The OSD still works fine on all of them.

I did a whole bunch of power cycling, reconnecting things, etc. I couldn't get the video to come back.


I have 1 unit where 15kHz outright failed, displays a weird rainbow colored thin column from top to bottom, no legible OSD. 31KHz works fine though. I had replaced a transistor (dont remember which, somewhere in the 15KHz circuit path) and it fixed the 15kHz! Then, it went out again, exactly the same way.

Did you try swapping the jungle/video daughterboard?


Top
 Offline Profile  
 
 Post subject: Re: Hitachi 27" 27MM20B Dual-Scan CRT TV??
PostPosted: Mon Jan 17, 2022 9:38 am 



Joined: 22 Jun 2005
Posts: 395
Location: Liberal cesspool
I just have to chime in once more and mention what a nice guy Josh is. He went out of his way for a total stranger and I feel I owe him more than just the small amount he asked for these things.

Thank you again Josh. You are cut from a different cloth.
_________________
A camel is a horse designed by a committee


Top
 Offline Profile  
 
 Post subject: Re: Hitachi 27" 27MM20B Dual-Scan CRT TV??
PostPosted: Mon Jan 17, 2022 2:56 pm 


User avatar

Joined: 16 Jan 2014
Posts: 1748
You're welcome! Amazing the difference in UPS shipping outright vs Ebay UPS shipping eh? Literally double.


Top
 Offline Profile  
 
 Post subject: Re: Hitachi 27" 27MM20B Dual-Scan CRT TV??
PostPosted: Thu Apr 21, 2022 9:07 pm 


User avatar

Joined: 16 Jan 2014
Posts: 1748
So my awesome friend @overlordmanny has done it again. Designed and printed a speaker cover replacement for the Hitachi sets. The stock covers are extremely brittle and some of the units I shipped had cracked or missing covers upon reaching destination. I asked him not to worry about latching tabs, these fit right into place and are meant to be secured with a few tacks of glue. They would need to be color matched painted to look original, any matte smoke gray color would probably work fine.

Although he is not asking for any money for these, I told him the least I can do is get him a few bucks for his trouble. It takes 3 hours to print one of these, so if anyone is interested, it'll be $10 per side + shipping.

Image

Image

Image

Image


Top
 Offline Profile  
 
 Post subject: Re: Hitachi 27" 27MM20B Dual-Scan CRT TV??
PostPosted: Fri Apr 22, 2022 4:37 am 



Joined: 22 Jun 2005
Posts: 395
Location: Liberal cesspool
You are my hero...at least this month. :)
_________________
A camel is a horse designed by a committee


Top
 Offline Profile  
 
 Post subject: Re: Hitachi 27" 27MM20B Dual-Scan CRT TV??
PostPosted: Tue May 10, 2022 9:57 am 


User avatar

Joined: 09 May 2005
Posts: 476
Location: Honolulu, Hawaii
Just a gratuitous Mushi 2 TATE VGA screenshot...

Image


Top
 Offline Profile  
 
 Post subject: Re: Hitachi 27" 27MM20B Dual-Scan CRT TV??
PostPosted: Tue May 10, 2022 12:48 pm 


User avatar

Joined: 16 Jan 2014
Posts: 1748
Both your units still working? My Ultravision Digital unit recently started making a arcing/snapping sound periodically, in which the screen blinks. I havent opened it up, but Im hoping its not the flyback. I have a couple spare units to work with, hopefully I can resolve the issue.


Top
 Offline Profile  
 
 Post subject: Re: Hitachi 27" 27MM20B Dual-Scan CRT TV??
PostPosted: Thu May 12, 2022 8:45 am 


User avatar

Joined: 09 May 2005
Posts: 476
Location: Honolulu, Hawaii
Yes, they both work fine. After fixing the blown HOT I've had no further problems. Still need to check more of the caps, and I have some ideas for a 15khz RGB mod, but I keep getting distracted with Xbox & Dreamcast games and haven't gotten around to it.


Top
 Offline Profile  
 
 Post subject: Re: Hitachi 27" 27MM20B Dual-Scan CRT TV??
PostPosted: Thu May 12, 2022 3:29 pm 


User avatar

Joined: 05 Nov 2019
Posts: 1005
Location: Massachusetts, USA
matt wrote:
Yes, they both work fine. After fixing the blown HOT I've had no further problems. Still need to check more of the caps, and I have some ideas for a 15khz RGB mod, but I keep getting distracted with Xbox & Dreamcast games and haven't gotten around to it.


Yeah, I am hoping to see someone finish working out the kinks for 15kHz RGB on these things! I don’t have one or need one, but I have enjoyed watching this whole Hitachi-saga play out.
_________________
For CRTs, A/V gear, video games & more, be sure to check out my eBay!

Image


Top
 Offline Profile  
 
 Post subject: Re: Hitachi 27" 27MM20B Dual-Scan CRT TV??
PostPosted: Thu May 12, 2022 7:19 pm 


User avatar

Joined: 09 May 2005
Posts: 476
Location: Honolulu, Hawaii
The problem is that they work so well with a line doubler that there's not much pressure to figure out a 15khz option.


Top
 Offline Profile  
 
 Post subject: Re: Hitachi 27" 27MM20B Dual-Scan CRT TV??
PostPosted: Fri May 13, 2022 10:04 am 



Joined: 08 Dec 2011
Posts: 33
does anyone have one of these for sale?


Top
 Offline Profile  
 
 Post subject: Re: Hitachi 27" 27MM20B Dual-Scan CRT TV??
PostPosted: Fri May 13, 2022 12:27 pm 


User avatar

Joined: 16 Jan 2014
Posts: 1748
matt wrote:
The problem is that they work so well with a line doubler that there's not much pressure to figure out a 15khz option.


This is precisely why I halted my work on the 15KHz RGB option. I got it working back on page 5, but it needed some more TLC for the brightness. I was still super busy packing and shipping and had just discovered how cool and easy it is to polish scratches from CRT glass, and my initial results looked so identical to a line doubler @ 31KHz I dropped the project.

Technically speaking, the only advantage for the 15K option over 31K is that the 15K should be brighter. The S-Video to these sets is among the best Ive seen, so thats another knock against spending more time on the 15K RGB option. S-video does seem to need some added attenuation on the luma line though as bright flashes cause a brief sync loss. That would be a worthy project, IMO.

Now IF someone could get a mod that would allow 15K RGB into the VGA port, as yatzr almost achieved, that would be cool. Im not sure if that will happen though.


Top
 Offline Profile  
 
 Post subject: Re: Hitachi 27" 27MM20B Dual-Scan CRT TV??
PostPosted: Fri May 13, 2022 8:22 pm 


User avatar

Joined: 09 May 2005
Posts: 476
Location: Honolulu, Hawaii
I think 15khz through the VGA circuit may be the best option. You could do an OSD mux mod through the TV side, but those Toshiba jungle chips aren't ideal for it. They have non standard input voltages and the brightness isn't adjustable from the user menu.

My impression, based on looking at the schematic and reading Yatrz's posts, is that you could run sync through the jungle chip while running RGB through the VGA amp.


Top
 Offline Profile  
 
 Post subject: Re: Hitachi 27" 27MM20B Dual-Scan CRT TV??
PostPosted: Sat May 14, 2022 2:04 am 



Joined: 04 Apr 2021
Posts: 58
Location: Seattle, WA, USA
From my experience and research, the jungle chip used in these TVs (Toshiba TA1268N) expect a 1Vpp RGB signal. If you just use a 0.7Vpp input, the brightness would be too dark. If you're going back to working on getting 15KHz RGB working on these sets, I suggest trying 180 ohm termination on your RGB lines and experimenting with different inline resistor values until you find the right combination. Just an idea.


Top
 Offline Profile  
 
 Post subject: Re: Hitachi 27" 27MM20B Dual-Scan CRT TV??
PostPosted: Sat May 14, 2022 7:21 am 


User avatar

Joined: 09 May 2005
Posts: 476
Location: Honolulu, Hawaii
Yes, I have a 13" Sharp TV with a TA1268N that I've modded. It does work if it's set up as you described, with the higher value termination resistors. It also clamps the signal at too low a level so blacks are crushed unless you increase the RGB cutoffs in the service menu. It works OK, but the lack of brightness adjustment is a nuisance. I'd hope that going through the VGA circuit would yield better results.


Top
 Offline Profile  
 
Display posts from previous:  Sort by  
Post new topic Reply to topic  [ 231 posts ]  Go to page Previous  1 ... 4, 5, 6, 7, 8

All times are UTC


Who is online

Users browsing this forum: No registered users and 10 guests


You cannot post new topics in this forum
You cannot reply to topics in this forum
You cannot edit your posts in this forum
You cannot delete your posts in this forum

Search for:
Jump to:  
Space Pilot 3K template by Jakob Persson
Powered by phpBB © 2000, 2002, 2005, 2007 phpBB Group