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I wish to create a new DMA/RAM expansion card for the Tandy 1000 line.

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  • blackepyon
    replied
    Originally posted by Eudimorphodon View Post
    I don't have the original Tandy board to compare it with, but it does definitely give me the willies how much insertion/removal force it seems to take to get boards in and out of these machines with the headers I've been able to find. I'm frankly worried the traces are going to start cracking after too many cycles.
    I'd say about 2-3x as much. This is fine if you're card doesn't have a back panel mounting bracket, and the socket is all that's holding it in place. Then it's not going anywhere.

    But you need to carefully wiggle it out a little bit each corner at a time.

    Leave a comment:


  • Eudimorphodon
    replied
    Originally posted by blackepyon View Post
    Yeah, the 62-pin headers I've been getting from Digi-Key are too tight. The first couple that I ordered from a different manufacturer actually did fit properly, but they went out of stock. I'd definitely be interested if getting a handfull if you can get or find ones that actually fit properly.
    I don't have the original Tandy board to compare it with, but it does definitely give me the willies how much insertion/removal force it seems to take to get boards in and out of these machines with the headers I've been able to find. I'm frankly worried the traces are going to start cracking after too many cycles.

    Leave a comment:


  • Eudimorphodon
    replied
    Originally posted by eeguru View Post
    Is there anyway they can do a proper double-tall male header with offset shroud like on the original RAM expansion Plus board? That way, whatever designs come out of this thread could be a proper replacement for the Plus RAM expansion allowing two more Plus boards to mount on-top.
    I haven't tested this yet because I'm currently not caring a lot about cross compatibility with original boards, but my ad-hoc measurements suggest that if I were to use a "double-ended" male header (they sell trimmable 2x40s at my local shop) and shim it while soldering I could get the "low" slot to the proper .7" spacing. (If you use a normal header you end up with .5".) Likewise using a normal header for the "high" slot and plugging in a set of trimmed "extra tall" stacking headers as an extender gets you about the right height for the upper slot. So it is *possible* to cobble it together. But it certainly isn't optimal. Shrouds would also be really nice. You could probably 3d print a sleeve to fit around the suggestions above but it wouldn't be fantastic.

    Leave a comment:


  • blackepyon
    replied
    Yeah, the 62-pin headers I've been getting from Digi-Key are too tight. The first couple that I ordered from a different manufacturer actually did fit properly, but they went out of stock. I'd definitely be interested if getting a handfull if you can get or find ones that actually fit properly.

    Leave a comment:


  • dJOS
    replied
    Originally posted by rkrenicki View Post
    Was the internal contact the issue, or a problem with the hole diameter in the plastic housing? I am planning on 100 in the first order, but at the prices thusfar quoted.. I would not be "too" upset if they were unsuitable.
    The holes Seemed fine, the internal connectors were stiff to start with and just gripped way too tight.

    I only wasted $100, but it was still frustrating.

    Leave a comment:


  • rkrenicki
    replied
    Originally posted by eeguru View Post
    Is there anyway they can do a proper double-tall male header with offset shroud like on the original RAM expansion Plus board? That way, whatever designs come out of this thread could be a proper replacement for the Plus RAM expansion allowing two more Plus boards to mount on-top.
    I do not really have a need for such a connector, but if this works out okay, I can point you in their direction to see if you want to give them a try to make one.

    Originally posted by dJOS View Post
    I’d be interested, however having been down this rabbit hole before and pouring a bunch of cash down the drain, I’d caution you to get a very small sample to test first. The batch I bought worked but where so tight that I nearly destroyed my Tandy ram expansion removing them. I ended up binning the lot.
    Was the internal contact the issue, or a problem with the hole diameter in the plastic housing? I am planning on 100 in the first order, but at the prices thusfar quoted.. I would not be "too" upset if they were unsuitable.

    Leave a comment:


  • dJOS
    replied
    Originally posted by rkrenicki View Post
    I am working with a vendor in China to have some proper 2x31 headers made up rather than piecing together 2 other sized headers, or getting a 2x32 and chopping off one row. Once I get the particulars worked out, I will share my vendor, or if anyone wants a few.. I am planning on ordering plenty of extras.
    I’d be interested, however having been down this rabbit hole before and pouring a bunch of cash down the drain, I’d caution you to get a very small sample to test first. The batch I bought worked but where so tight that I nearly destroyed my Tandy ram expansion removing them. I ended up binning the lot.

    PS I gave them the data sheet for the ones I had been using and they still got it wrong some how.
    Last edited by dJOS; November 16, 2019, 04:52 PM.

    Leave a comment:


  • eeguru
    replied
    Originally posted by rkrenicki View Post
    I am working with a vendor in China to have some proper 2x31 headers made up rather than piecing together 2 other sized headers, or getting a 2x32 and chopping off one row. Once I get the particulars worked out, I will share my vendor, or if anyone wants a few.. I am planning on ordering plenty of extras.
    Is there anyway they can do a proper double-tall male header with offset shroud like on the original RAM expansion Plus board? That way, whatever designs come out of this thread could be a proper replacement for the Plus RAM expansion allowing two more Plus boards to mount on-top.

    Leave a comment:


  • rkrenicki
    replied
    I am working with a vendor in China to have some proper 2x31 headers made up rather than piecing together 2 other sized headers, or getting a 2x32 and chopping off one row. Once I get the particulars worked out, I will share my vendor, or if anyone wants a few.. I am planning on ordering plenty of extras.

    Leave a comment:


  • bladamson
    replied
    Wow, that right-angle PCB jobbie looks a lot better than I was expecting!

    Nice job.

    Leave a comment:


  • blackepyon
    replied
    So, I got the PCBs from China. I haven't fully assembled the card yet, but I did enough to see how well the right-angle solder jobbie works.
    IMG_20191115_220354127.jpgIMG_20191115_220410354.jpgIMG_20191115_220427772.jpgIMG_20191115_220444166.jpg

    I did one side of the backpanel section without any solder mask. Turns out I did get a couple measurements wrong, but this is why I submitted them as two separate files rather than having it as a break-off section. The vertical alignment of the holes is off by about .100 or so, and the holes for the PEM nuts need to be a hair larger. Once I get the next backpanel board run and confirm it works, I want to use this to create a template that other people could build their cards onto.

    One note about using PEM nuts with CR4, don't over-tourque the bench vise, and make sure the PCB side has a smooth piece of metal as a shim, so you don't wreck the shiny bits. In a future iteration, I'll probably move the LED hole a bit further away from the holes, because it did crack slightly when I over-clamped it, leading me to shave off a little bit of the sides of the board to make it square again.
    Last edited by blackepyon; November 16, 2019, 07:56 AM.

    Leave a comment:


  • blackepyon
    replied
    Originally posted by RetroGaming Roundup View Post
    Tandy was an insane place that made choices that amplified whatever Commodore did with things like the C64 disk drive crippling. They would spend a dollar to save a dime and figured the end user would never notice. Check out our recent podcast that features a talk by Paul Schreiber who tells what Tandy was like in those days. We will also be having one of the buyers from the 1000 era on soon.
    If you weren't the kind of person to notice the shortcuts taken, you probably weren't the kind of person to care. The only reason WE noticed, is because we've had to dive this deep into the hardware. Bottom line is that the customer got a functional machine for a reasonable price. THAT, I'd argue, drove the home PC market more than the IBM "personal" computer ever did (though I have a soft spot for old IBMs as well).

    Leave a comment:


  • Eudimorphodon
    replied
    Originally posted by Eudimorphodon View Post
    there seems to be an issue with DOS Kermit; a weird, funky issue that's going to force me to break out my second eBay V-20 to absolutely confirm it. Fun stuff!
    So it seems like I've got me a head-scratcher. I went ahead and swapped a V-20 into the HX rig; as a result I was able to verify that ctmouse is indeed fixed by having a V-20... but Kermit wasn't. Kermit is behaving very badly on the HX with my integrated serial+IDE card, with transfers just bombing out, even after upgrading the CPU to the same that's been in the EX since I started using it. So apparently it's not the CPU like I thought.

    I'm worried of course that there's some kind of issue with the card, but if I yank the stack out of the HX and stuff it into the EX Kermit works fine. (And this is running with the same boot drive, RAM configuration, everything.) Also, if I fire up ProComm with the same serial port speed/parity/etc settings that seems to also work fine on the HX. (And the mouse works... etc.) Now the *really* crazy thing: in one test I disabled both serial ports on the combo card (so it's just doing IDE duties), put my stand-alone card into the other slot jumpered to the same ports (COM1/COM2)... and that time it worked.

    Apparently I need to find something else to exercise the serial port with. Some of how Kermit is behaving is almost making me wonder if there's some kind of BIOS difference between the machines, because on the HX the program sometimes blinks the screen when updating, which I don't see on the EX... but there's still that thing where it worked the one time with the stand-alone serial card. I really am starting to wonder if the HX does have "something" about it, a different version of some ASIC, that renders it a little more unstable than the EX, and for *some* reason it's smelling something strange about having the IDE and UARTs behind the same '245. (Which is the only difference between the unified card and the two separate ones in the prototype run.) But why does Procomm work?!

    Leave a comment:


  • RetroGaming Roundup
    replied
    Tandy was an insane place that made choices that amplified whatever Commodore did with things like the C64 disk drive crippling. They would spend a dollar to save a dime and figured the end user would never notice. Check out our recent podcast that features a talk by Paul Schreiber who tells what Tandy was like in those days. We will also be having one of the buyers from the 1000 era on soon.

    Leave a comment:


  • Eudimorphodon
    replied
    Originally posted by blackepyon View Post
    The keyboard controller has pins controlling sound and floppy, and the parallel port controller manages some of the floppy controls as well. And the relationships change between each model.
    While working on my HX project I noticed all the weirdness hanging off the keyboard controller. Of course, to make it more fun the EX/HX technically have two chips you could call the "Keyboard Controller" onboard, the actual "keyboard controller" in the standard PC sense (but also moderates those other peripherals) and the 8048 MCU that actually *scans* the matrix keyboard, which is only connected to the other by a few lines. I haven't verified by looking at the other machines' tech manuals but I assume that everything downstream of the serial connection between the 8048 and the keyboard controller is roughly what you'd find in a normal detachable Tandy 1000 keyboard. But it's still interesting, or maybe it's actually *less* interesting because it's too conventional, that Tandy laid things out like that. I'm kind of surprised they didn't come up with a unified keyboard controller ASIC that directly scanned the matrix.

    Leave a comment:

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