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Thread: My first Sol-20!

  1. #31
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    16x 2102 does indeed equal 2K. Some of that is video RAM, right?

    If you deposit stuff to memory, you should be able to dump the memory and see it, unchanged. If the program is running away it's entirely possible that it's clobbering memory as it goes. Something must be working though, or the SOLOS ROM wouldn't come up at all.

    Quote Originally Posted by falter View Post
    Any recommendations on a RAM board for this thing?
    Many RAM boards will work, static is easier to debug than dynamic, but this is a front panel-less machine so dynamic will probably work pretty well. I would get something that's pretty low power since the SOL-20 doesn't have a huge supply and it's pretty small in there for heat dissipation. There are of course Processor Tech RAM boards to look for, but something like a CompuPro RAM16 or other 6116-based SRAM board would be a good choice for quick, easy, get-it-up-and-running operation.

    I've got a few tested/working RAM boards, PM me if you need one.

  2. #32
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    It is funny that a single AS6C4008 SRAM (or the like) affords more RAM that you could fit in the PT box with traditional S100 boards. (512K x 8 SRAM). There are even larger SRAMs, but most of those are 3.3V.

  3. #33
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    Quote Originally Posted by glitch View Post
    M'eh, if they don't blow up within an hour or so of full supply voltage, you've probably driven the moisture out and/or blown out the tantalum crystals. I don't recall PT boards being especially bad for low-quality tantalum capacitors. Now, North Star boards...
    I have gotten weird intermittent behavior with them on more than one Sol20, that the moment you change the caps, they work fine and consistently. I have only had one blow up one on a Rev-E Sol20.


    On the RAM subject, a Sol20 with out an S100 memory card is useful only as a Terminal in "Solos" using the TERM command. You will need to get a ram card, if you don't have one already, get a tested one from Glitch, I have never had a problem with anything I have gotten from him.

    Cheers,
    Corey
    Last edited by Corey986; October 29th, 2017 at 03:49 AM.

  4. #34
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    I guess this is what happens with the tantalums:

    https://www.reddit.com/r/retrobattle..._guy_with_the/

  5. #35
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    Yeah, they sometimes blow up. Like Chuck(G) said, it's typically from tantalum crystal growth which creates little shorts between positive and negative terminals. Small crystals get blown out when power is applied -- capacity may be reduced but the cap lives on. Big crystals blow the cap apart or smoke it or actually set it on fire. It's usually related to moisture getting into the cap through the encapsulation.

    Some manufacturers' component choices seem to be more prone to blowing up than others. I've personally found North Star boards are pretty bad to have caps randomly go on you, I just completely recap North Star boards nowadays, I don't even test them beforehand.

    Corey, your observed flakiness could be from a reduction in capacity or it might be a symptom of the foldback current limiter in the SOL-20 power supply. The current limiter is an *excellent* design and one of several very strong features of the SOL-20, but I've noticed similar flakiness in some boards in my test jig, which uses a Lambda adjustable current limited supply. Sometimes intermittent boards will immediately blow a capacitor in e.g. the IMSAI, which has no current limit and runs a bit high on the voltage rails. All speculation on this particular situation, of course

    Quote Originally Posted by Corey986 View Post
    You will need to get a ram card, if you don't have one already, get a tested one from Glitch, I have never had a problem with anything I have gotten from him.
    Thanks for the positive recommendation! Soon I hope to have a SOL-20 in my test bench lineup, so I should even be able to confirm hardware for SOL-20s directly in a real SOL-20 (vs. an IMSAI with a SOL-20 like setup).

  6. #36
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    Oh I'm sure the flakiness is related to the caps losing capacitance. As you mention capacitance gets reduced as the small crystals get blown out. For ceramic caps it's easy you can bring them above the Curie point for a few minutes and for electrolytics, as long as they aren't leaking, you can reform them using a variac, but the tantalums I think all you can do is replace.

    Cheers,
    Corey

  7. #37
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    Yeah, the "self-healing" nature of some tantalum varieties means the cap doesn't totally fail, but AFAIK there's no way to rebuild capacitance, so you're stuck with replacing.

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