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Thread: TRS-80 Model 16 workalike from parts?

  1. #1

    Default TRS-80 Model 16 workalike from parts?

    Hey guys. I've wanted a model 16 or 6000 for several years, and lost an ebay auction for a 16B-HD fixer-upper earlier in the day.

    However, ebay was bugged and not updating, so I didn't realize I'd been sniped at the last moment, and ended up with the machine's hard drives (from another auction ending 30 seconds later), which I can't use now. I thought I'd won the machine, so I switched tabs and bid on the disks quickly and won them. Doh.

    Stupid of me, I know. Haha. C'est la vie. I guess that's what I get for being a last-minute bidder!!

    But anyway, instead of trying to resell them (especially since I don't have a way to really test them properly), I thought maybe I could kinda build a Model 16 workalike from a Model II. I'd be using a floppy emulator and an MFM simulator eventually anyway, so the single single-sided 8" drive wouldn't really be a problem, and I might even replace/supplement it with a 5.25" unit anyway just to make writing disks on a PC easier. I see a couple of Model 16 68k CPU and RAM cards for sale. I read something about modding the 256k RAM card to take a Meg or more, so I figure that would get me running Xenix. I guess the Model II doesn't come with the MFM controller either, right? So I guess I'd need that, too.

    It looks like if I were careful and made good buys, maybe on stuff that needed fixed a bit, that I could put together a Model 16-alike for less than or at least equal to what the Model 16s seem to be selling for nowadays. I mean, to upgrade the II to a 16, you just have to add the appropriate cards, right? There's no motherboard swap or anything, right?

    What do you guys think? I don't really know as much about TRS-80s as I'd like (especially the big ones), so I am not sure if it would be a good path to take or not.......... Is it possible to hop up the Model 16 CPU card to run at 6000 speeds?

    Thanks.
    -- Lee
    If you get super-bored, try muh crappy YouTube channel: Old Computer Fun!
    Looking to Buy/Trade For (non-working is fine): TRS-80 Model II,12,16,6000, Mac IIci hard drive sled and one bottom rubber foot, Hercules card + mono monitor (preferably IBM 5151), Multisync VGA CRTs, 040 or 601 card for Mac IIci, Decent NuBus video card, Commodore PC(286+), PC-era Tandy stuff, Aesthetic Old Serial Terminals, Amiga 2000 or 3000UX

  2. #2

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    The path you are proposing was actually an available Tandy upgrade: the Enhanced Model II. You'd get the 6Mhz 68000 CPU and Memory boards plus an upgraded power supply, at a minimum.

    To upgrade your II to a 16/6000, you will need:

    1. 68000 CPU Board - preferably the 8Mhz version that came in the 6000, but was also available separately to upgrade Model 16s to 6000 specs. But, these are insanely rare. The early 6 Mhz boards are more common and will run XENIX 1.x but not XENIX 3.x unless they had a PAL upgrade. This PAL upgrade has not yet been reverse engineered by the community so you would have to find an already modified 6Mhz CPU card if you wanted to run XENIX 3.2. There is also a recent patch to XENIX 3.2 that allows you to run it on the older 6 Mhz boards without the PAL upgrade. So, you can pretty much do almost anything with the 6Mhz boards, albeit a bit slower in most cases.

    2. 68000 RAM Board - there are two versions of this board. The early version the came with the M16/16B and maxed out at 256K. The later one in the 6000 maxed out at 1MB. But, you can install multiple memory boards. And they can be modded above their stock max capacity.

    3. A11082 Power Supply - most Model IIs have the A11080 or A11081 power supply. This needs to be upgraded to an A110082 to supply enough power to run the 68K boards. There are also newer aftermarket options available that would require a custom installation.

    4. HD Interface Board - There are 3 versions of this board. The early Type 1 interface supports the SA1000 based 8MB HD only. The Type 2 interface supports the later 12MB and greater Tandy HD units (like the ones you purchased). The Type 4 is a combo interface/controller and only requires a MFM bubble.

    5. All the M2/16 Tech Bulletins should be applied.

    There you go...that's what you'll need.

    One of the most rewarding vintage computer experiences I have found is to get XENIX running on a Model II.

    Good luck and ask around here for help anytime!

  3. #3

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    Quote Originally Posted by pski View Post
    2. 68000 RAM Board - there are two versions of this board. The early version the came with the M16/16B and maxed out at 256K. The later one in the 6000 maxed out at 1MB. But, you can install multiple memory boards. And they can be modded above their stock max capacity.

    !
    Do you have details of how the 256K card can be modded above its stock max capacity? I've 2 x 256Kb cards in my 16A and would love to have 512+ on a single card so i can have the Hi-Res card in as I've run out of slots.

  4. #4

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    Quote Originally Posted by Tarkie101 View Post
    Do you have details of how the 256K card can be modded above its stock max capacity? I've 2 x 256Kb cards in my 16A and would love to have 512+ on a single card so i can have the Hi-Res card in as I've run out of slots.
    I have not attempted it, but there is one approach detailed here: https://github.com/pski/model2archiv...ix/mhz-megmods

    Other approaches used RAM chip stacking or higher capacity RAM chips, but there is little that can be found on these in order to duplicate them. There are some enthusiasts designing modern plug-in RAM boards but none have been released yet. There is no technical barrier preventing us from reproducing one of these modified boards, ie. the stacked RAM chip approach, it's just a lot of effort. It will require someone to sit down and figure out how to rewire some of the address signals, perform the modifications (a lot of tricky soldering to stack the chips), test it and document it. I will eventually do it if no one else does, but that won't be in my schedule for a long time. Who's up for the challenge?

  5. #5

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    Thanks Pete, reading.....................

    Steve

  6. #6
    Join Date
    May 2011
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    Default

    On the topic of memory boards, has anyone considered just laying out a new RAM board for these machines using AS6C4008s or similar static RAMs? I don't know much about the 2/16/6000 series, but taking a peek at the Model 16 service manual it looks like what makes the board "complicated" is the RAS/CAS/Timing circuitry for the DRAMs. A 1MB board made with AS6C4008s probably wouldn't need much more than a pair of the SRAMs and a GAL for address decoding and slightly massaging the 68000 control lines.
    My Retro-computing YouTube Channel (updates... eventually?): Paleozoic PCs

  7. #7

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    Thanks guys! This sounds more interesting than just buying an already set-up model 16 or 6000 anyway.

    I don't think the early PALs of that era could have contained any flip-flops or state machine type stuff, so if I could get hold of one long enough to build a truth table, I could probably replicate it with a GAL. That sounds like it might be a pretty useful thing for the community.

    If a PSU upgrade is required, I 'spect I'd probably retrofit a modern PSU into the enclosure, rather than trying to locate an original one. Probably significantly cheaper and significantly more reliable.

    Two more questions, if y'all don't mind:

    1. Is there any kind of adapter board design out there (or specifications that I could use to implement my own with a Teensy, although I'd rather not do it from scratch) to connect a PC keyboard to the Model II? None of the ones I am seeing for sale come with a keyboard.

    2. I read something last night about not all Model IIs coming with the backplane and card cage, or something? Or maybe I am confusing it with the Model 12... I guess there's no way to tell from auction pictures that only show the exterior, whether it has one or not?

    Thanks again, fellows. You are gentlemen and scholars.
    -- Lee
    If you get super-bored, try muh crappy YouTube channel: Old Computer Fun!
    Looking to Buy/Trade For (non-working is fine): TRS-80 Model II,12,16,6000, Mac IIci hard drive sled and one bottom rubber foot, Hercules card + mono monitor (preferably IBM 5151), Multisync VGA CRTs, 040 or 601 card for Mac IIci, Decent NuBus video card, Commodore PC(286+), PC-era Tandy stuff, Aesthetic Old Serial Terminals, Amiga 2000 or 3000UX

  8. #8

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    Oh yeah, the Model II has that fuzzy TV-style CRT too, doesn't it? I guess there's no green tube that's a drop-in replacement, eh? I think I'd want to put one of the graphics boards in it at some point, too.


    Edit:
    Quote Originally Posted by Eudimorphodon View Post
    On the topic of memory boards, has anyone considered just laying out a new RAM board for these machines using AS6C4008s or similar static RAMs? I don't know much about the 2/16/6000 series, but taking a peek at the Model 16 service manual it looks like what makes the board "complicated" is the RAS/CAS/Timing circuitry for the DRAMs. A 1MB board made with AS6C4008s probably wouldn't need much more than a pair of the SRAMs and a GAL for address decoding and slightly massaging the 68000 control lines.
    I was thinking exactly the same thing, but I wanted to get hold of a machine and get it working before I toyed with the idea any further. I figured I'd get a Model II with 64k or whatever they came with first, get it working and booting, and then investigate making a meg or two SRAM board to go with the 68k board, rather than using up all the slots with 256k RAM boards to get Xenix running comfortably.
    -- Lee
    If you get super-bored, try muh crappy YouTube channel: Old Computer Fun!
    Looking to Buy/Trade For (non-working is fine): TRS-80 Model II,12,16,6000, Mac IIci hard drive sled and one bottom rubber foot, Hercules card + mono monitor (preferably IBM 5151), Multisync VGA CRTs, 040 or 601 card for Mac IIci, Decent NuBus video card, Commodore PC(286+), PC-era Tandy stuff, Aesthetic Old Serial Terminals, Amiga 2000 or 3000UX

  9. #9
    Join Date
    May 2018
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    Are these what you are looking for ?

    (nothing to do with me, I must add)

    CPU Board https://www.ebay.co.uk/itm/Tandy-TRS...L/202979587665

    RAM Board https://www.ebay.co.uk/itm/NOS-TRS-8...AAAOSwVcZc0LDE

    Just noticed its the 6MHz

  10. #10

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    Quote Originally Posted by bladamson View Post
    1. Is there any kind of adapter board design out there (or specifications that I could use to implement my own with a Teensy, although I'd rather not do it from scratch) to connect a PC keyboard to the Model II? None of the ones I am seeing for sale come with a keyboard.
    http://www.vcfed.org/forum/showthrea...apter-features

    Quote Originally Posted by bladamson View Post
    2. I read something last night about not all Model IIs coming with the backplane and card cage, or something? Or maybe I am confusing it with the Model 12... I guess there's no way to tell from auction pictures that only show the exterior, whether it has one or not?
    All Model IIs have a backplane as it is the motherboard for that computer. The card cage was optional on the 12 though.

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