Tandy video mod

Hardware questions and modifications

Tandy video mod

Postby KenG » Wed Nov 23, 2016 1:17 pm

OK, I decided to use one of my less than perfect motherboards as a test. It works fine, except the pins that supply sound to the monitor are broken. The ports are a real weakness on this machine. I use an adapter to get to a VGA monitor, so I use the audio port anyway. I expect this mod would take an experienced person about an hour. Took me 3 or 4! I almost put the chip in backwards. Thankfully caught that. Thought I had it done. Machine worked but no Tandy graphics and some other weird stuff. Took it back apart. One of the pins came loose while I was soldering the wires on. Fixed that. It now works! I put my Jr-IDE and backpack 3.5" drive on it. Everything seems to work OK.

Have to think about this some more. May try it on a better motherboard, may not. I did learn a few things. I used too thick of wire. Often lost other end trying to line up to solder second connection. Thinner, maybe even stranded wire should be easier to work with.

Anybody have a list of games that work with Tandy graphics on the Jr? Ultima one supports Tandy graphics but doesn't seem to pick up the mod. Is there a way to force?
Enhanced PCjr with a jr-IDE (1GB DOM) and a parallel port side car with a compact flash reader and backpack 1.44mb floppy attached. Tandy video mod.
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Re: Tandy video mod

Postby GHiero » Wed Nov 23, 2016 4:01 pm

Try ULTIMA T
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Re: Tandy video mod

Postby KenG » Wed Nov 23, 2016 6:26 pm

No go on that. Oh well. Actually the CGA graphics aren't bad.

Had better success with Pool of Radiance. Set pool.cfg for Tandy graphics and WOW! What a dirrerence. Play is real slow but the graphics are way better. Starting to think it was worth the effort.
Enhanced PCjr with a jr-IDE (1GB DOM) and a parallel port side car with a compact flash reader and backpack 1.44mb floppy attached. Tandy video mod.
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Re: Tandy video mod

Postby GHiero » Thu Nov 24, 2016 5:33 am

Unfortunately, it does not work and I lost the scan of the IBM PC reference card for the Ultima Trilogy, which may have indicated a command line argument to force Tandy graphics mode. Forcing Tandy with "t" does work in Ultima 4 and 5, but I believe you can only force CGA in Ultima 1 with "c"
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Re: Tandy video mod

Postby KenG » Thu Nov 24, 2016 2:42 pm

Thanks for the info. I have the complete Ultima collection on CD. I may fool around with debug to see if I can figure out where and how video modes are set. If I can find that, I could force Tandy mode. I can always copy back from the CD later if I want the regular version.
Enhanced PCjr with a jr-IDE (1GB DOM) and a parallel port side car with a compact flash reader and backpack 1.44mb floppy attached. Tandy video mod.
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Re: Tandy video mod

Postby Trixter » Thu Nov 24, 2016 9:14 pm

KenG wrote:I use an adapter to get to a VGA monitor


You buried the lead!! What adapter do you use to convert RGB TTL to VGA?

Play is real slow but the graphics are way better.


320x200 16-color mode is twice the amount of memory to sling around, so there is a speed penalty. You may find it useful only for games not involving action.
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Re: Tandy video mod

Postby KenG » Fri Nov 25, 2016 7:35 am

I will look up the information on how I built it and post later. I found most of the information on here, but in bits and pieces. It would probably be nice to have it all in one place. I put it together and then bought a panel monitor with speakers for $25 at goodwill. It is very nice.

The games probably aren't any slower than they were on my C128 back then. I have just been spoiled.
Enhanced PCjr with a jr-IDE (1GB DOM) and a parallel port side car with a compact flash reader and backpack 1.44mb floppy attached. Tandy video mod.
KenG
 
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Re: Tandy video mod

Postby KenG » Fri Nov 25, 2016 10:36 am

Ok, the information on the RGBI to VGA converter is here: http://www.bit-c-128.com/buy

It was designed for the C128, but it works great with the Jr.
Enhanced PCjr with a jr-IDE (1GB DOM) and a parallel port side car with a compact flash reader and backpack 1.44mb floppy attached. Tandy video mod.
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Re: Tandy video mod

Postby jharre » Fri Nov 25, 2016 11:31 am

100_0780 (Medium).JPG
Here's a picture of the small DAC board and the larger Gonbes board.
(405.57 KiB) Not downloaded yet
KenG wrote:It was designed for the C128, but it works great with the Jr.


Yep, it works great here, too. I had picked up a couple bare boards from J. Alex a while back http://he-insanity.blogspot.com/ and was pleased. The digital to analog board takes a handful of parts including some 1% resistors and a fairly expensive DAC chip. But, dang!, it works!!

Add the Gonbes board (lots on eBay) to convert the signal to VGA, and a PCjr to CGA pigtail and you're in business.

It also works well to convert from CGA on a 5150/5160 to VGA as well.
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Re: Tandy video mod

Postby KenG » Fri Nov 25, 2016 1:54 pm

Yes, that pictue shows what I have. I bought mine, and the power supply, from the site I posted. He provides full instructions for connecting it to the Gonbes unit. I still haven't gotten around to mounting mine in a case. I have two weeks off over Vhristmas and New Years. I hope to get it done then. That would make it safer and easier to move around.

I did take me a couple of hours, on and off, to get the colors right. There are pots on the Gonbes board to adjust. I have a PCjr monitor, so I used it to compare. I have it pretty close. I think my monitor is a 17 inch. Problaby wouldn't go bigger.
Enhanced PCjr with a jr-IDE (1GB DOM) and a parallel port side car with a compact flash reader and backpack 1.44mb floppy attached. Tandy video mod.
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