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    EEVblog #1056 – Digilent Open Scope MZ Review

    Dave looks at the Digilent Open Scope MZ Review, an $89 open source oscilloscope, logic ...

    • wlinaz

      Dave, it looks like the “reset” dip is still in the “on” position.

      • motocoder

        Yes, three of us have pointed this out now.

    • Michael Rempel

      Caps. It is almost always caps. Just whack them all. That is why they dont fix them, it is quite a bit of work.

    • Peter O’Neill

      Dave, just a thought, without the power on reset chip the unreliable system boot maybe due to the reset pulse being to short from the RC network. Whereas when you were using the probes to release the reset the processor had been in reset a very long time and system boot did occur each time.

    • Peter O’Neill

      Just read the datasheet for the processor, and min reset hold time is 20 clock cycles, so disregard my previous post.

    • David Byrne

      It might be worth hitting the device with isolated heat/freeze once it is at the intermittent stage. If you change the intermittency of the fault with heat/freeze, it might help locate the fault, whether it be a failing component issue or some other weird fault like poor raw card etching, cracked track or dry joint even.

    • 82uJ

      Don’t think long enough about this, but first impression is may/must
      be part of the M16C/62 integrated soft-watchdog capabilities. In this
      case, the reason can be at the far other end as with this hard-reset.

      Yust my 2¢ for my first posting here, after, and to do learning much from Dave 🙂
      … love it, really!
      (…”hmmmm, that’s smell like …, porn on a stick”) LOL (y) 😉

      thanks for all and greets from Germany

    • motocoder

      The reset DIP switch is ON right up until the end of the video…

    • Paul

      couldn’t you freeze spray caps put some power on and see if a cap thaws out quickly

    • Michael Rempel

      I had a dream about this last night. Stupid but true. Anyway what if that cap was supposed to make a saw tooth wave form to regulate the brightness of the LEDs? Makes sense to me anyway, you adjust it by moving the bias up or down to suit. And yeah that will account for almost all your current draw delta. But it doesnt explain the power on problem with _RESET_ However if the supply is marginal after 10 years that would not surprise would it? My guess is make a little daughter board to poke the reset properly and put back the timing cap or make a reasonable facsimile. That seems to me to be a reasonably easy pair of things to do. But then I AM a programmer, and that sort of problem is never going to defeat me, especially not for something as simple as an intercom. By rights you should be able to whip one up right smart with a wad of chewing gum and an arduino board. Well OK, you can have a Raspberry Pi if that makes it easier, just because you have some audio synthesis to do.

    • Steve Beckman

      The RESET/ trace on the PCB has to be going somewhere else – maybe it runs under the micro and out to other circuits through a VIA. Your measured current draw on the RESET/ pin with the micro pin lifted was much more reasonable. Suspect that the dip switch has something to do with it.

      • 82uJ

        “Suspect that the dip switch has something to do with it.”
        That’s my impression too.

    • sak

      Is there a possibility that although the 5V rail is there, it doesn’t end up on the MCU’s VCC pin for one reason or the other? That could explain why the system starts to work with an almost 0 Ohms resistor connected to it’s reset pin. It gets it’s power from the reset pin’s protection diode.

    • tlhIngan

      The company may be speaking the truth in that they don’t make new ones anymore, and because of that, the manufacturer no longer offers a support contract for it. Yes, they probably could get one off ebay or something, but that likely has its own issues and means they need to support that.

      A large amount of gear is “tossed” because it falls outside of support, or is no longer supported/manufactured by the manufacturer. Depending on the company, this may mandate immediate replacement with supported hardware under a new support contract, or replacement deferred until the equipment fails, depending on whether or not downtime is acceptable.

      As for compatibility, yes, it’s probably compatible, but that also means having to go through and integration test the new system with the old – just because the module is compatible doesn’t mean you can plug it into the old system. Things change and perhaps the building is using an odd configuration that was deprecated because the manufacturer thought no one used it. Then there are behavioral changes – perhaps the users expect things to work a certain way but because of other things in the firmware, yes, you have to do something else now.

      So yes, the company can probably install a new model for that one panel (and probably are), but they were asked to do an exact replacement to which they couldn’t supply that, because now the new module is probably a bit more expensive, but now there’s a lot more labour involved in ensuring the new module works with the old system and there aren’t any issues that require an emergency rollout because say, the garage door doesn’t work at 4AM because it misinterpreted a command. Or more seriously, perhaps the protocol was expanded and the old system can’t gracefully handle the extensions which say, if someone punches in a code, causes the entire system to crash.
      The bus drivers are probably in the audio module – there are plenty of wires going to the audio box, and the audio box is probably standalone and since every intercom needs the audio box, that makes sense to put the bus drivers and interface there. Especially since the wires for the bus are on the audio box.

      And is it me or did Dave not actually try to wire up a reset switch just to see if maybe his reset circuit isn’t working properly?

    • Wayne Holder
    • Rainer

      Could be a hairline crack, because it works best when you press the probes on the board to pierce through the coating. Try bending/pressing the board while powering up?

    • Bill

      Hi Dave,

      did you succeed in repairing this module?
      Maybe I can give some advice because I worked for the company who made this thing.
      The problem seems to be on the display module, but 99% of the time it isn’t.
      One easy way to check if this module is working is by putting the dip switch n°4 ON
      and the text should appear and scroll. Once you checked if it works this way, put this switch back to OFF position.
      The main module on this system is the Speaker/Mic module GF-DA.
      Most of the time the GF-DA doesn’t receive power from the supply module GF-BC that you have to find on the building.
      Normally you should measure at least 20 volts on the R1/R2 wires coming from the GF-BC (see the installation manual page 6 and 7).


      Once you have the this voltage on R1/R2, everything will work again.
      By the way, your videos are always very interesting.
      Bonjour from France.

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