VOGONS


First post, by T-Squared

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Yes, it has happened! My system is as complete as it will ever be, so I might as well show it off here.

I got a dual-lot of Sanyo MBC-775s in 2019 as a present for myself, because it was such an interesting computer that I heard about through Reddit. (Sorry to Jim Leonard, I know you wanted this back then! I'm happy to know you finally got one, though! I'm always available for parts if you need them!) I can't find the reddit post that got me interested, but I was impressed with how it looked. The system uses a dual-board configuration, with CGA, ISA, and Floppy Controllers on one, and the CPU, memory, and parallel port at a 90-degree-angle on the other. Unfortunately, one of the CGA/ISA/Floppy boards was not working (which I saved in-case it can be repaired someday.), and the CRT board on one was cracked, so I could not use it. However, the other CPU/Mem/Parallel board DOES work.

The cover is not attached because it allows me easy access to the internals of the machine. Besides, the plastic has become brittle and several pieces have broken off of the covers; not to worry, though, I have stored all the intact and non-working parts safely away. (The other CRT board I decided not to repair, but I have kept several large parts from it that have come in handy.)

Some may question my reasons for modifying this system (including wasting a boatload of the original 120ns memory chips), but part of it was for future-proofing. At the very least, sockets will allow for future expansion, should we develop parity-centric memory boards (barring the MicroRAM board). The other was because I wanted to see how far I could take the capabilities.

Anyways, It's been a long 6 years, and I have become more knowledgable about not only this computer, but the IBM 5150/5160 series computers in-general.

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What is new:

  • A better CPU - V20 instead of 8088
  • A mouse, larger memory, and a real-time clock - An AST SixPak card
  • Better and faster memory - 640kb of 100 nanosecond memory instead of 256kb of 120 nanosecond
  • Better graphics - a 16-color EGA card instead of 4-color integrated CGA graphics
  • and An extra ISA slot - thanks to a motherboard connector modification and a card slot board that I designed, permanently home to an XT-IDE-CF Mini. (4th image)
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I am so surprised at how much this system can run now. As you can see in images 1, 2 and 3, I was able to run not only "Super Solvers: Treasure Cove!", but also Commander Keen episodes 1 and 4 (AND 5, I would later find!)

I recently was able to run a few more games in EGA, including Captain Comic, Duke Nukem 1, and Reader Rabbit: Ready for Letters!

The only problem I've run into, and might be part of the system, is that the colors are not correct. (as you can probably see in the 2nd and 3rd image) Reds Blues, and Greens are barely contrasted, Dark Gray (Color 09) barely shows up, and most of the light colors, including Light Gray/Dark White (Color 08) don't contrast at all. Even the contrast dial, when turned up all the way, doesn't do much. I'll see if replacing the CRT neckboard drive transistors does anything, though.

Despite that, the system does amazingly well for its age, and I love the contrast between games and user interfaces that we consider for more advanced systems, versus the bulky "control-room" styling of the MBC-775. (I think that's called "Cassette-Futurism".) I'm almost expecting to see someone sending a distress text message to it as if it were a technological relay station! 😜

Reply 1 of 3, by keenmaster486

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Very nice. I'm impressed with the extra slot modification. Any chance you could post more pictures of that and reveal more about how you designed it?

I have some questions:
1. Does it use an 8284 to generate the CPU clock, thus making it overclockable with a "PC-Sprint"?
2. Are those single or double sided drives?
3. Any chance of a sound card?

Also, with respect to the CRT issues, it kind of looks like the dot pitch of that tube is a bit coarse.

World's foremost 486 enjoyer.

Reply 2 of 3, by T-Squared

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The extra slot is a simple 1:1 breakout board. i.e. there are 62 pins on the header that I found on one of the logic boards, the exact number of a normal ISA slot, with traces going from Pin 1-Header to Pin 1-ISA, Pin 2-Header to Pin 2-ISA, etc.

I have 2 extra boards if you're interested ($15, with S&H not yet included), with a BoM here: https://forum.vcfed.org/index.php?threads/san … d-free.1252393/

1. Not sure. The number of the chip sounds familiar. Although, the system is designed to use an 8088-2 CPU, which means that it can run at 8mhz.
EDIT: 1a.: I think it does use one. This system is basically an IBM XT with inexact pin connection between chips. (i.e. the basic logic is there, but which gates used on each chip differs from an ACTUAL IBM XT)
2. I think they're single-sided.
3. I tried a Sound Blaster sound card, to attempt Adlib playback, but it kept coming up with an error. (Although that was when it had 256kb ONLY. I haven't tested it with 640k.)

Reply 3 of 3, by keenmaster486

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Cool. 8 MHz would make Keen much more playable, especially Vorticons. Also, all of the official Keen games will run: 1-6 and Dreams. What won't run is modern source mods such as Foray in the Forest that are compiled with 286 optimizations since it's too bulky to run well on an 8088 anyway.

Well, to be honest, Keen 4-6 already really needs a 286 to be truly playable. But they at least made the attempt. If you turn off the score box and the music and you have a turbo XT, it becomes somewhat tolerable. Another tip: turn off SVGA compatibility. It will cause a slowdown whenever the game scrolling hits the edge of video memory, and you only need it on certain SVGA cards.

Also I can see geometry problems on that CRT. Tbh you probably have a lot of electrolytics in there that have gone bad and need replacing, after 40 years.

World's foremost 486 enjoyer.