• Please review our updated Terms and Rules here

VR241 substitute for Rainbow, VT240, etc.

L

Lou - N2MIY

Veteran Member
Joined
Apr 1, 2008
Messages
1,306
Location
Albuquerque NM / Potomac MD
So for the past few weeks I have been working hard on repairing a trashpicked 42" plasma monitor. It's a 10 year old Pioneer PDP-424MV. It's not a TV, because it has no tuner, but it has tons of inputs on the side. I trashpicked this beast in the hopes that 1.) I could fix it and 2.) it could be a VR241 replacement. Will and I had been talking over the years about what could replace a VR241 in a simple manner. I actually bought a $30 RGB to VGA scan converter, but it needs clean composite synch and I did not build the LM1881 synch stripper yet. But then I saw this monitor in the trash about a month ago. So far 1.) I have fixed it and 2.) it looks like it might work as a VR241...

It was a bear to fix. One of four switching supplies on the y-sustain board was not working. The plasma engine is an NEC and there are no print sets anywhere for the engine. I had to reverse engineer the switching supply. Of course, it was a bad cap, but it sure took me a while to find it. It works now though. It does have bad screen burn also, but it was trashpicked. It was a little diversion from the RL02 emulator that had been burning me out....

So, this evening I hooked up the Rainbow. A while back I made this little box/cable affair for connecting both the VR241 and a VR201 to the Rainbow at the same time:
http://www.vintage-computer.com/vcforum/album.php?albumid=204&attachmentid=14603
http://www.vintage-computer.com/vcforum/album.php?albumid=204&attachmentid=14604
http://www.vintage-computer.com/vcforum/album.php?albumid=204&attachmentid=14602
http://www.vintage-computer.com/vcforum/album.php?albumid=204&attachmentid=14605

From the photos you can see there is a little box that breaks out the signals from the 15 pin monitor connector on the back of the Rainbow. The usual VR201 cable plugs into one side, where I also have a phone handset jack for the keyboard. The other side has a high density 15 pin connector. I have wired this connector with R,G,and, B drives wired to the usual VGA pins. No other pins are used (real VGA includes H and V synch lines, but the Ranibow does not have them, it's synch on green.) The little switch either connnects green drive or the monochrome drive to the VGA connector. (Remember, the Rainbow has two video subsystems, one monochrome, and one RGB. On the DEC VR241 cable, R, G, and monochrome as green get connected to the VR241. The real green drive is there, but never gets used in any dec cable.)

So, I use a standard VGA breakout cable to get R,Gs,B out to nice BNC connectors. The monitor has a slew of connectors, including R,G,B,H,V as BNC jacks. I wasn't sure if this plasma monitor would do synch on green, but it did!
http://www.vintage-computer.com/vcforum/album.php?albumid=204&attachmentid=14606 (blurry, sorry)
http://www.vintage-computer.com/vcforum/album.php?albumid=204&attachmentid=14600 (I always liked the game SCRAM!)
http://www.vintage-computer.com/vcforum/album.php?albumid=204&attachmentid=14601 (I'm an engineer, so gotta have CAD)

The down side is that I cannot get all the horizontal scan lines displayed. It's a 480 line monitor, so it should work. I have to study the manual. I will report here if I figure out the settings.

My long term plan is to put this in the garage as a monitor for the VT240.

Keep your eyes peeled for people getting rid of 10 year old monitors...

Lou
 
Pretty nice work with the splitter box and getting the color signals onto the flat panel.

I know you mentioned that the green is never used on any DEC cables, but it is fun to configure the Rainbow to drive monochrome and RGB simultaneously. The original plan for the Rainbow was to support dual monitors (one color with graphics, one mono with text only), but the problem of who had what monitors was complex enough that DEC scrapped plans to support it. The may have built a Y cable (I think there's a part number for it, but I've never actually seen one).

However, that doesn't mean you can't drive both color and mono simultaneously. If you're programming your own graphics programs, it's straightforward to enter dual-monitor mode. The Rainbow docs lay it out, actually. Also, some of DEC's GSX-86 distributions also included dual monitor drivers. You just need to feed green to the color monitor rather than mono. Fun stuff! I currently have a homemade plug for driving two monitors, and I've written some trivial software in C and Pascal to use it. It's also possible to patch GW-BASIC I believe.

Cool stuff you've got there!
 
Those Plasma units are wonderful. I had the slightly older 4:3 model and it was incredible after it got a tuning.
I broke it unfortunately when I leaned it against a desk, bumped it with my chair and the fall was enough to crack the envelope. IT can take three months to fix a TV and half a second to wreck it. x(

I know you mentioned that the green is never used on any DEC cables, but it is fun to configure the Rainbow to drive monochrome and RGB simultaneously. The original plan for the Rainbow was to support dual monitors (one color with graphics, one mono with text only), but the problem of who had what monitors was complex enough that DEC scrapped plans to support it. The may have built a Y cable (I think there's a part number for it, but I've never actually seen one).
Click to expand...

I know that I've seen multi-monitor setups on the Rainbow. I just don't remember where.

Edited: Yes There was a dual monitor rig at VCF East 2.0
 
Sorry to hear about the broken tube. I would have been pissed.

I have a typo in the original post that I can't edit now. I wrote "On the DEC VR241 cable, R, G, and monochrome as green get connected to the VR241." of course I meant to type "On the DEC VR241 cable, R, B, and monochrome as green get connected to the VR241."

I never played with any true dual monitor applications. I am of course still looking for ACAD V2.6 which does support dual monitors.

That display in the photo looks very nice. There appear to be two different images on the VR201 and VR241, so obviously that fellow had either written his own or had found some dual monitor programs to show off.

One other comment on the plasma monitor. When driven from the rainbow, it reports running at 640x240, and interestingly this is not reported in the Pioneer or NEC literature as a supported mode, but it was in there. Unfortunately, I was never able to find an adjustment that would get all the horizontal scan lines onto the screen. However, the entire width of the screen does fit. It does work out nicely as a text-only monitor, since the top few scan lines of the top line of text can be missing without too much loss.

I had to put the whole setup away since I do not have the room to leave this out, but it was fun. In a few months I will play with a $30 RGB to VGA scan converter that I picked up. I plan to put it in a little enclosure with power supply and synch stripper. I'll start a thread on that when it's finished, but it'll probably be a winter project.

Lou
 
NeXT said:
I know that I've seen multi-monitor setups on the Rainbow. I just don't remember where.

Edited: Yes There was a dual monitor rig at VCF East 2.0
Click to expand...

Yes, that would be me in the picture. It was running a custom Turbo Pascal program that would draw graphics to the VR241 while simultaneously printing text to the VR201. That's the configuration DEC had planned - the VR201 would remain tied to the Rainbow's onboard monochrome text display, and any graphics would be fed to the VR241. The Rainbow can provide graphics to the (Red, Green, Blue) signal lines, the (Red, Monochrome, Blue) signal lines, or the Monochrome signal line alone. No other combination is possible (for example, driving RGB signals and monochrome all with graphics). So the monochrome signal, instead of being switch to produce signals from the graphics board, remains connected to the text generator hardware instead. It's very easy to do, but the two monitors would never display the same image as only one can display graphics at a time.

Almost any Rainbow graphics program can be changed to support dual-monitors with a little Microsoft DEBUG magic (basically instructing the graphics card to output on Green rather than Monochrome). The utility of said changes is somewhat questionable, of course. I do believe Autocad supported the Rainbow's dual-monitor modes. Digital Research's GSX-86 for the Rainbow included dual monitor drivers. There may have been a handful of others that worked with it. I think Lotus 1-2-3 might have supported it (you could leave a graph up while continuing to do whatever). I'm sure I'm forgetting some.
 
I know for a fact that AutoCAD did support multiple monitors. Again, I've seen someone setup with a drawing one one screen and a console on the other.
 
I have been swamped at work lately, but needed to spend some quality time in the workshop and at the bench yesterday and today. I worked on a quick project allowing one to substitute a VGA monitor for a VR241.

At the heart of the project is a Gonbes GBS 8200 RGBS to VGA converter. This $30 board made for arcade game conversions almost does it all. It does not however, work with synch on green as provided by the VT240/Rainbow/Decmate II/Pro. It needs to be provided with clean synch, so I grabbed it off the green with an LM1881.

Here is the finished product: http://www.vintage-computer.com/vcforum/album.php?albumid=204&attachmentid=16645 .

And here's what's inside the box: http://www.vintage-computer.com/vcforum/album.php?albumid=204&attachmentid=16644 . There is a small switching supply on the left from the junk pile. In the middle rear is the GBS 8200, and in the rear right is the LM1881 (more clear here:http://www.vintage-computer.com/vcforum/album.php?albumid=204&attachmentid=16639).

There are other photos in the album that are closups of the front and rear panels.

It is surprising how well this little board works. There is no way I could build a scan doubler for what this thing costs! It's really quite good. Here is a closeup from the setup screen of the VT240: http://www.vintage-computer.com/vcforum/album.php?albumid=204&attachmentid=16638 and http://www.vintage-computer.com/vcforum/album.php?albumid=204&attachmentid=16637. The digital camera does not do it justice. I have the VT240 in color mode, and the screen is a trashpicked repaired Princeton SL70 from year 2003.

The GBS 8200 has menus with all the adjustments needed to fit the output on the screen perfectly, as well as adjust the color / brightness / contrast / etc. It would be perfect if it did synch on green, but that was easily addressed. If you've been thinking about a project like this, just do it. You will not be disappointed.

Lou (Happy New Year!)
 
I bought the GBS 8200 from here :http://www.hollandcomputers.com/sto...lder-arcade-systems-to-LCD-monitors-p6052.htm

The shipping was fast and reasonable. They are in the US. I have also seen these boards on ebay and from Asia. This vendor above seems to be quite good and has a lot of arcade game restoration supplies.

The TI/National LM1881 is dead common, but of course Jameco (http://www.jameco.com/webapp/wcs/stores/servlet/Product_10001_10001_107140_-1) is my favorite because they are so hobbyist friendly!

You're on your own for the snazzy wood sided 1980's styled enclosure..... (Thanks Will !!)

Lou
 
Last edited:
You must log in or register to reply here.
Back
Top