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Display Telecommunications Corporation "Megaboard".

SomeGuy

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Ok, have been exploring this early-ish clone board lately, here is what I have found:

dtcmegaboard.jpg

This is a Display Telecommunications Corporation "Megaboard". I don't know if it was always called that, or if they referred to it differently when part of a complete OEM system. It is not labeled as such.

The DTC "Megaboard" is an early ~1983 IBM XT clone motherboard. Note this is not the same "DTC" that produced hard disk controller. Also do not confuse with "DTK".

It was the first product of Display Telecommunications Corp. It was sold to OEMs and individuals as bare boards, kits, or assembled. It was used by hobbyists, experimenters and high-tech handypersons.

There is an Infoworld article comparing it to other boards here:
https://books.google.com/books?id=B...Q6AEIFDAA#v=onepage&q="dtc megaboard"&f=false

One ad lists:
Display Telecommunications Corporation
4100 Sprint Valley Rd, #400
Dallas Tx 75234
Bare board $99
Socketed: $249.95
Assembled $599.95

DTC did sell cases and other parts for it.

After clipping a shorted -12v tantalum capacitor, the board works great. Going by the chip dates, this specific board was manufactured in 1984.

The ROMs contains a bootleg of the IBM 5160 11/08/82 BIOS with BASIC. From my research, it normally should have come with its own "megabios". Also from what I have read, supposedly the manual gave instruction how to copy the IBM ROM in to it, which some considered inappropriate.

This board uses the same power supply interface as the PC/XT/AT. A standard AT supply works fine with it.

The board is physically larger than an XT board. It will not fit in an XT or Baby AT case. The Keyboard plug does not line up and the board needs extra space for its reset switch. Still, it is mostly an XT clone and uses the 5160 ISA spacing.

The board itself feels a little flimsy. All chips are socketed. On the one hand, socketed chips can be a bit less reliable, but on the other hand, could be easier to fix. I haven't looked up all of the part numbers, but It uses only basic 74LS chips to interface the main chips. (No PAL programming needed?)

An odd implementation on this board, it has little metal divider shields between the main sections. While that was common on some earlier computers, I don't believe I have seen that on other IBM PC clone boards.

Over all, this is a "no frills" motherboard, but it does have some developer-friendly aspects.

Most visibly, it has perfboard area where one can their own custom circuitry. It features a reset switch next to the keyboard port.

This board supposedly "features" slot 8 support identical to the IBM XT. Although, what was that ever used for? The board also has a card-edge connector that seems to extend the ISA slots.

Jumpers permit ROMs to be configured in a variety of ways.

By cutting/soldering jumper wires, the board can be configured to use either 16k, 64k, or 256k, RAM chips. This board contains a full 640k, although the Infoworld article suggests it would be limited to 256k.

This board has also been maxed out with an NEC V20 and a math co-processor.

Booting it, and throwing software at it, it seems perfectly IBM PC XT compatible. It passes all the diagnostics I have thrown at it. It works fine with VGA, XT keyboards, and an 8-bit 1.44mb floppy controller. Of course, remember this has an IBM BIOS in it.

The only real issue with this motherboard is that it does not physically fit a standard XT case.

Any rate, I think this in an interesting addition to my collection of early PC clone and parts.
 
I didn't realize copying the IBM Basic ROMS was so common, this XT clone board I have
also came with a copy of IBM Basic.

DSCF0089.jpgDSCF0090.jpg
 
Growing up, our first computer was a DTC Megaboard clone. In fact, this machine is still in my parents' attic, so someday I will attempt to restore it.

We had the OEM case which fit the board nicely. It had an oval-shaped cutout for the keyboard and reset switch (similar to PC 5150), and the lid was hinged so it opened up rather than sliding off. The front bezel was designed to look like an IBM only it had horizontal decorative lines instead of the vertical ones on the IBM. It had a rear power switch, and a black "Fortron"-branded power supply. I'm fairly certain it was all bought from DTC that way. I don't have any pics of it, as it's 1000 miles away.

We had the "MegaBIOS" with it when we got it, however it was replaced at some point down the road with an ERSO BIOS probably due to some hardware compatibility issue (HD floppy drive, video card, maybe?), and unfortunately the original MegaBIOS chip was set aside and is probably gone forever now. I have a clear memory of the POST test booting up with the message "TESTING MEMORY /" (with a / \ flashing back and forth).

I still have the original OEM manual and documentation for it. It goes into great detail about the theory of operation (logic diagrams, scope readings, etc) and also has the listing for the infamous "IBM MEMORY to INTEL HEX CONVERTER" BASIC program that allegedly lets you copy IBM BIOS ROMs (have never tried it) in order to "facilitate patching".

Here's a few pics of some of the pages from the book:

mb_cover.jpgmb_prod.jpgmb_pic.jpgmb_dip.jpgmb_basic_hexcov1.jpgmb_basic_hexcov2.jpg

There doesn't seem to be a lot of info out there about the company beyond what you posted. I assume they probably stayed mostly a mail-order clone company, and just couldn't afford the R&D to stay competitive and eventually folded up. If anyone has any more story about what they did after this, I'd be really curious too.

FK
 
Update - I managed to get the case out of storage and snapped some photos. The hard drive is of course non-functional, and those floppies need servicing but that original PSU started right up with good voltages on all rails. Interestingly the company, Fortron (not to be confused with Fortran or Voltron) is still in the power business today.

The switched, standard AC outlets on the back were a nice feature so you could plug in a non-IBM monitor and I think we plugged in our printer too (before the days when we knew we should have a surge suppressor strip).

I'm really interested to find an image of the original "MEGA-BIOS" bios chip, just to make it all complete. If anyone has that actual chip, would love to get a dump of it for archival purposes.

FK
 

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There's something awry with the PM's. I got you PM's frankiekat and see a sentence or so in the notification email. When I go to the forum to read them they just show as blank (although yesterday I was able to read one of them). The one you sent with those pics shows the pics but no text. The text must be there somewhere. I can confirm that my case appears identical to yours. PSU is branded differently but also looks like it might be the same.

Hmmm, just looked again the the PM's are no longer blank. Will reply now.
 
There's something awry with the PM's. I got you PM's frankiekat and see a sentence or so in the notification email. When I go to the forum to read them they just show as blank (although yesterday I was able to read one of them). The one you sent with those pics shows the pics but no text. The text must be there somewhere.
That is a known ongoing issue that has been occurring since the hosting software (vBulletin) was upgraded at the VCF in April.
Discussed in a few threads within the 'Vintage Computer Forum Support' section.
Appears to be related to PM's with still-under-moderation members.
 

2022 Update!​


The MEGA-BOARD is nearly restored.

I cleaned up and polished the case and removed some small rust patches. I also bent back the rear bezel as best as I could, sanded and re-painted it.

The power supply popped a Rifa cap after an hour or so of run, so the HV section of the PSU has been re-capped and the noisy airplane-engine fan has been replaced with a near-silent Noctua (yes I kept the original fan and the mod is completely reversable).

I fully serviced the floppy drives and unfortunately the original B drive had one completely dead head however I was able to track down an identical parts drive and now both drives are working.

Not pictured is that 10MB Miniscribe 2012 MFM hard drive from earlier photos, which I was also able to revive.

One thing still missing!​


I'm still looking for the original "MEGA-BIOS" BIOS ROM that was apparently written in-house by DTC and sold with it. Has anyone here ever had or seen this ROM before? If not, any suggestions or ideas for where or how I might find someone who might? :)

According to the pricing sheet, they sold the ROM assembly listing for $19.95 which would be amazing - though I'd expect it to be about as rare as hen's teeth!

Thx!
FK
 

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Very nice, thanks for posting these. So it is a flip-top case, awesome. It looks like the case might be able to fit a regular XT motherboard, but due to the cutouts on the back it looks like an XT or XT clone power supply would not quite fit.

I haven't seen the mega-bios anywhere.
 
Very nice, thanks for posting these. So it is a flip-top case, awesome. It looks like the case might be able to fit a regular XT motherboard, but due to the cutouts on the back it looks like an XT or XT clone power supply would not quite fit.

I haven't seen the mega-bios anywhere.

Yes, it's a flip top - here's another pic that shows it a bit more. The original MB is slightly non-standard size, however over the years we had "modified" the case to fit more standard sized boards as the bottom of the case has a lot of other holes drilled in it. Also, if it looks like in the pictures that the expansion card mounting bracket seems to be missing something on the right side, it's because part of it was hack-sawed out at some point probably to accommodate a different motherboard somehow.

The PSU is, as you mentioned, very non-standard with the rear-facing switch. Both of those NEMA outlets are switched, so that was kind of nice you could plug in your monitor and printer and have just one switch. The power connector headers on the MB are round pins - not like the more rectangular style that is more standard - and the PSU connector mates with it. I can recall we had built a little adapter harness when we used that PSU with a later 286 board in the case.

That burn mark in the rear left of the case top I can recall was from an internal modem that died dramatically from an electrical storm, and amazingly nothing else was damaged. I intentionally avoided that area when cleaning up the case to preserve that little piece of it's history!
 

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Alrighty, we are trying to document all motherboards on the planet and this one is missing it's manual. I see one of the members has that and we would like to add that to the page for this board:
we also found a variant:

(Since I can't DM yet)
 
Alrighty, we are trying to document all motherboards on the planet and this one is missing it's manual. I see one of the members has that and we would like to add that to the page for this board:
we also found a variant:

Interesting - looks like that's three variants of it, one with original DTC logo silkscreen and two clones. I don't have a clean picture of mine with the board entirely removed handy so attaching the closest I can find right now (I know for sure mine is original from DTC since we have all of the documentation from buying it new). I do have the complete bound manual above, which has logic diagrams, schematics, theory of operation - basically a version of the IBM technical manuals. It's probably 100 pages and bound, though someday I do plan to take it apart and scan it all - and will of course submit it to Retro Web.

Unfortunately, the ROM images aren't the original DTC "Mega BIOS" ones. The ERSO in my picture was a later "upgrade" and the original DTC ROM was lost to history. Apparently, you could have purchased a paper listing of the source code to it as well, but we didn't opt for that and I'd imagine that's even more rare than the ROM itself. I went so far as to try to find some of the original employees to see if they had any leads or more info, unfortunately the founder of the company passed away in 2014 and none of the others that I emailed ever got back to me. Would love to know a bit more about the company's short-lived history and how it came together. According to the obituary he was involved with Xerox and the original development of the mouse so would have been really cool to hear some stories about what he did and who he worked with back then!

Thanks for the update!

640KB
 

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In '84, I bought a bare DTC Megaboard plus all the components required, including the BIOS *and the BIOS listing*.
I still have everything in my possession. At the end of the boards' useful lifetime, I started to tinker with some of the connexions, mainly to make it run faster, so it is not working as it is.
If this has significant interest, I could scan the paperwork, but it's hundreds of pages, so I'll only do it if someone *really* wants me to.
See you !
Finn, Brittany, France
 
If there is any chance you could dump the content of the BIOS, that would be very appreciated.

I'd be interested in seeing the documentation, but I realize it can be a lot of work to scan. Is this in a bound manual or loose pages? Does it have fold-out? If it is only has loose pages, a document scanner with a document feed should be able to scan them very quickly.
 
I have no access to an Eprom reader right now, but I'll try to see what is possible.
I have started to scan the listing of the BIOS. It's around 180 loose pages, so it's manageable.
Where can I deposit the result when I have finished ?
As a bonus, I've tried to do some OCR on the listing and it works reasonably well, so maybe I can recreate a complete textfile that can be fed to an assembler.
I join the ad that triggered my investment forty years ago.
 

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I have no access to an Eprom reader right now, but I'll try to see what is possible.
I have started to scan the listing of the BIOS. It's around 180 loose pages, so it's manageable.
Where can I deposit the result when I have finished ?
As a bonus, I've tried to do some OCR on the listing and it works reasonably well, so maybe I can recreate a complete textfile that can be fed to an assembler.
I join the ad that triggered my investment forty years ago.
Oh wow! That would be amazing! I can't believe you have not just the BIOS but the ultra-rare BIOS listing... what a find!

I have the DTC bound user manual - the one that has all of the theory of operation and the full schematics. It's in the original spiral binding so I've just been hesitant to rip it out to properly scan... but if you scan the BIOS listing, then it's the least I can do to preserve the history of this board!
 
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An odd implementation on this board, it has little metal divider shields between the main sections. While that was common on some earlier computers, I don't believe I have seen that on other IBM PC clone boards.
In your original post, you mentioned the metal strips on this board.
These are power supply rails to facilitate power distribution on this double sided board.
The scanning of the BIOS listing is in progress. How do I upload the result to the Retro Web ?
Finn
 
In your original post, you mentioned the metal strips on this board.
These are power supply rails to facilitate power distribution on this double sided board.

That's neat. I had no idea those were power rails - just assumed they were for some kind of shielding. Very cool!

The scanning of the BIOS listing is in progress. How do I upload the result to the Retro Web ?
I think the easiest way would be to join their Discord (https://discord.gg/HWWH7hsk2p) and then post it in the "new-site-content" channel.

BTW, I have started scanning the users manual that I have as well. Do you have that (the one with the schematics in it) and have scanned it also?
 
I think the easiest way would be to join their Discord (https://discord.gg/HWWH7hsk2p) and then post it in the "new-site-content" channel.
I'll try that.
BTW, I have started scanning the users manual that I have as well. Do you have that (the one with the schematics in it) and have scanned it also?
I scanned the schematics back then but not the rest of the manual.

Latest news : I finished the scan of the BIOS ! I ran it through tesseract to create a searchable PDF document. 108 Megs raw PDF, 85 megs once compressed into ZIP.
I've opened an account on Discord, but my file seems to be too big to permit upload...
 
Update: The PDF of the MEGA-BIOS source listing has been optimized down to 6MB and posted here:

 
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