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Thread: Tarbell Floppy controller modification

  1. #11
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    Quote Originally Posted by Chuck(G) View Post
    Well, if there were a demand, it wouldn't be difficult to make a TO-3 shaped PCB. Maybe glitch wants to do some--not my thing.
    Sure, we can run an adapter board if folks are interested in that! Those EzSBC modules are usually pretty well built though, I don't think I could probably run a similar module for less, not fully assembled + tested.

    Quote Originally Posted by Chuck(G) View Post
    You have to wonder what's drawing the current. I have the original Tarbell 1771 floppy board and it uses regular 78xx TO-220 regulators that don't get overly hot. I don't remember that 8257 DMAC getting really hot on my other boards.
    Could just be really poor/zero airflow. I have a bunch of Vector Graphic ZCB boards from embedded applications where basically they were stuck in a box with no airflow, they're all very discolored around the regulators, even though that's not a board that runs hot.

  2. #12
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    Quote Originally Posted by glitch View Post
    I don't think I could probably run a similar module for less, not fully assembled + tested.
    Thats why I was thinking of just an adapter board for the 50 cent Chinese ones, like
    https://www.aliexpress.com/item/32796268715.html

    I don't know if they are small enough to fit between the TO3 holes yet, though.

    Grabbed a picture, looks like they are around .3 x .8" TO-3 hole spacing is 1.8"
    so they would fit easily

    Screen Shot 2019-08-24 at 9.40.44 AM.jpg

    A hexagon would even work for the pattern, and it would panelize easier
    Last edited by Al Kossow; August 24th, 2019 at 08:44 AM.

  3. #13
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    Yup, the same ones are available on Amazon and eBay in bulk for about a buck apiece, if you don't like waiting for shipment from China. There seems to be a choice between one with a trimpot for voltage adjustment and one with a fixed resistor divider.

  4. #14

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    Quote Originally Posted by Dwight Elvey View Post
    . Changes in orientation can make a difference. The one used on this board was likely the worst from what I recall but it is only a small difference.
    Dwight
    I think S-100 boards do a lot better when they are mounted vertically because of the convection air currents. In the case of the SOL-20, with the boards horizontally, heat building up between them is a real problem, especially for the ones closer to the top of the pile. So I added a small fan to blow air between them to help keep them cool and it made a big difference along with keeping the pre-regulator voltages as low as possible.

  5. #15
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    The fan blowing through the card stack was a standard option for multibus cages.

    One of the reasons that I don't like the PC system of expansion cards. The NEC c-bus was better in this respect as the card contacts were opposite the mounting bracket, so air could be blown through the stack.

    Too bad we're stuck the system now.


  6. #16
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    Quote Originally Posted by Chuck(G) View Post
    Tthe card contacts were opposite the mounting bracket, so air could be blown through the stack.
    The PCB layout also flows better. Looking at the NEC card all the bus buffering is to the left of the Ethernet IC.
    Apple's implementation of Nubus copied the same mistake putting the DIN connector next to the output fence.
    IBM didn't make that mistake with Microchannel, but then PCI moved it back.
    Note that it is not necessary to open the box to insert the NEC card, and you can use a lever to insert/remove cards.
    You don't have short length cards, so there is a card guide on both edges.
    VME, and HP's DIO, even S-100 are other examples of doing it right.

  7. #17
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    Quote Originally Posted by Al Kossow View Post
    Other than having the pinouts to the board the same, no.
    I ended up just buying some cheap modules and will make a board with the TO-3 pinouts and solder them onto it.
    a friend just made this up for me
    adapter.jpg

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