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DEC Rainbow modern display options

C

crivett95

New Member
Joined
Jun 18, 2018
Messages
8
Location
Troon, Scotland, UK
Hi,

I have a DEC Rainbow 100B which has the colour graphics option fitted. When I received the machine late last year, it had a faulty VR201 with it which was unfortunately beyond repair. As a replacement I made up a cable to use the composite input on a TV instead. While this works, it isn't perfect as it is only monochrome and none of the many TVs I have tried it on display the full picture as part of the left hand side of the image is always cut off. I am now looking for a way to hook the machine up preferably to a VGA monitor or TV with VGA input to support colour (and hopefully get a full image) as I can't find any replacement original monitors and also lack the space to keep one around.

Does anyone have any experience in getting a Rainbow to output to a modern display in colour?

Thanks!
 
I'm sorry to hear that you think your VR241 is beyond repair. I'm not sure what that means since I repair everything. I might only call a bad CRT "beyond repair".

Yes, I have connected my Rainbow (and the VT240, which in color would use the same VR241 monitor) to other monitors. The Rainbow output is RGB with synch on green. I am away from home at the moment or else I would look up the number of scan lines, etc. in my notes. You can look that up yourself on the internet however. There should be old threads right here on the forum with that data.

I have a Pioneer plasma (yes, I got it broken and fixed it) that I use : http://www.vcfed.org/forum/album.php?albumid=204&attachmentid=14600 . I like having a giant display for my VT240.

Also, I have used an arcade game board to go to VGA for display on a VGA monitor (See here and the other photos in this album: http://www.vcfed.org/forum/album.php?albumid=204&attachmentid=16642) I did have to use an LM1881 synch stripper to separate the synch from the RGB to satisfy this board. The heart is a board called GBS 8200 which is still on Ebay for $20USD.

This should give you plenty to chew on. Or perhaps you can fix your VR241 ...

Lou
 
The R* has a weird resolution, something like 800 x 240 lines. If the picture is coherent and a part of the screen is truncated, I would think that could be remedied via one of the trimpot controls. To display that video on a vga though you would need some sort of scan doubler. If I'm right about the 240 vertical lines, that's exactly half of standard vga. Scan doublers for Amigas are common and run around 100$. Not saying they'd work right out of the box though.
 
A̶r̶e̶ ̶y̶o̶u̶ ̶s̶u̶r̶e̶ ̶i̶t̶'̶s̶ ̶R̶G̶s̶B̶?̶ ̶I̶'̶v̶e̶ ̶g̶o̶t̶ ̶t̶h̶e̶ ̶t̶e̶c̶h̶n̶i̶c̶a̶l̶ ̶m̶a̶n̶u̶a̶l̶ ̶f̶o̶r̶ ̶t̶h̶e̶ ̶D̶E̶C̶ ̶R̶a̶i̶n̶b̶o̶w̶ ̶a̶n̶d̶ ̶t̶h̶e̶ ̶v̶i̶d̶e̶o̶ ̶o̶u̶t̶p̶u̶t̶ ̶i̶s̶ ̶d̶e̶s̶c̶r̶i̶b̶e̶d̶ ̶a̶s̶ ̶b̶e̶i̶n̶g̶ ̶a̶ ̶c̶o̶m̶p̶o̶s̶i̶t̶e̶ ̶s̶y̶n̶c̶ ̶s̶i̶g̶n̶a̶l̶ ̶a̶n̶d̶ ̶t̶h̶e̶ ̶v̶i̶d̶e̶o̶ ̶c̶o̶n̶n̶e̶c̶t̶o̶r̶ ̶o̶n̶ ̶t̶h̶e̶ ̶R̶a̶i̶n̶b̶o̶w̶ ̶d̶o̶e̶s̶n̶'̶t̶ ̶s̶p̶l̶i̶t̶ ̶i̶n̶t̶o̶ ̶R̶G̶B̶ ̶o̶n̶l̶y̶ ̶c̶o̶m̶p̶o̶s̶i̶t̶e̶.̶

Never mind me, didn't see you had the color option installed! :rolleyes:
 
Perhaps the original poster does not have time nor skills to engineer a solution....The display you want is a VR-241a with the associated cable. Maybe you'll get lucky and find one of these in your area.
b
 
With the color output being analog RGB with sync-on-green, it should be very possible to use an external scan converter to connect up a VGA display. The Gonbes GBS 8200 is a cheap, if subpar, solution; the open-source scan converter (OSSC) might also work.
 
It has slightly noisy analog output, the scaling is terrible (nearest-neighbor), and some combinations of model + resolution produce random white "speckles" because they are driving the RAM too hard (ie. RAM not fast enough). There is a fix for the latter issue; a google search can locate it.
 
"For what this board cost" is the operative phrase. If you need to get something up and running, the board is fine for that purpose. But it's not going to win any quality awards.
 
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Thanks for all the replies, I didn't expect so many!

Unfortunately the VR201 I received with the machine was thrown out, it never had a VR241 with it despite having the graphics option (which I have successfully ran diagnostics on) for some reason. I'm guessing that's because the main use for my Rainbow was running dBase under CP/M. The VR201's CRT was covered in lots of cataracts and the capacitors must have leaked really badly as an unbelievably large amount of red goo/liquid was leaking out of it. I guess someone with a lot of time and patience may have been able to attempt a repair, but it was beyond my ability to do anything with sadly.

I think I've settled on trying to use a GBS 8200 and sync separator to connect a VGA monitor as I managed to pick one up for £20 shipped and have the bits to build a sync separator based on the LM1881 on the way as well. Even if its not perfect, it'll be a lot better than any of the solutions I've used to get a video output from my Rainbow so far, so for the price I'll be quite happy if it all works. I'll report back on how I get on as I should have time to get it all built and set up next week providing all the parts arrive on time.

I have already made up a cable to go from the Rainbow's video output to VGA so I should hopefully be all set after I have pieced together the VR241 replacement from the GBS 8200 and LM1881 :)
 
Hi, just posting a quick update on how I got on with my quest to get a colour monitor working.

I did go down the GBS 8200 route at first and built a sync separator for it. This did work and with some adjustment, the left hand side of the screen was intact, however the output had quite a bad green tint to it when displaying in monochrome and occasionally it would loose sync. I never found out what the cause of this was, sometimes it worked fine and others it didn't. When switching between DOS and Windows 1.0 it would also need the image readjusted on the GBS 8200 itself, so while it was an improvement in many ways, it wasn't perfect.

Eventually, due to having enough other machines that could take advantage of it as well to justify the high cost, I invested in an Open Source Scan Converter (OSSC). This worked great with the Rainbow out of the box using the Rainbow to VGA cable I made earlier for the GBS 8200 board. All I had to do was set the AV3 (VGA) input to expect RGsB and the Rainbow worked first time. I did have issues with the left hand side of the screen still being cut off when using my TV, however on connecting to the HDMI input on my PC monitor, these issues vanished and I had a nice clear and full image from the Rainbow :D I also didn't have to make any adjustments when the video mode of the Rainbow changed when switching between DOS and Windows like with the GBS 8200.

If you can justify the cost, I would recommend the OSSC over the GBS 8200 as it works much better out of the box especially when used with a PC monitor instead of a TV and also does not require a separate sync separator circuit. Here is a video I made of it in action :cool:

 
Thanks for the update! Someday I'll run out of CRT318h monitors for my M24 series and will have to do the same. The OSSC doesn't always work with every input and output combination, but when it does work, it works great.
 
One word reply. Smashing.

You could also go with one of these, purported to work vintage gear by at least 2 forum denizens:

https://www.ebay.com/itm/NEC-MultiS...e=STRK:MEBIDX:IT&_trksid=p2060353.m1438.l9372

Cheap if you're in the US and maybe Canada. Or find an equivalent in your area. I think it has to be 19" and have an fxp or uxp suffix.

Is it more economical to build it as a kit or source your own parts? The OSSC that is.
 
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