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EEVblog #1334 – Mystery Dumpster Teardown

Mystery dumpster teardown time! With the most amazing mechanical mains power switch you’ll ever see! ...


  1. Hi Dave,

    Nice buy. Wondering what you had to shell out for it. I think that you have to keep in mind that 7 1/2 to 8 1/2 DMM’s were never high volume products for anyone other than HP and even then I would bet that they we probably less than 50K units. Look at the Solartrons their construction is similar. I would bet for the few bucks you paid that anyone of us would hop on it in a New York minute for a working one. I wonder what the real stability of the Prema is. I have a HP3456A that had not been calibrated in over 25 years that was still in spec. That’s real performance.


  2. Please push down all those socketed chips. That EPROM has nearly worked itself out of the socket. Guaranteed almost every one of those things will make a pop as it drops back into the socket.

  3. Re Serial Numbers
    In my experience companies don’t like starting serial numbers at #1.. often choosing to start at a 1000, or 100000, I think there’s a customer expectation that serial #5 means you probably haven’t ironed out the bugs yet. So I wouldn’t be at all surprised if your device wasn’t only the 41st off the production line.. I’ve noticed this with a few of your vids where you assume serial number 10xx is the thousandth machine made.

    • Well, that’s all I have to go by, supposing a company starts at given higher number is probably just a much a risk as assuming they started at zero. It could very well be the 1041st unit, we don’t really know?

    • If the company has a good implemented numbering system even the first engineering devices built will have a unique serial number.
      So when the first devices are sent to the customers — depending on the device we are talking — they will have a serial number bigger than 1 and maybe even bigger than 100 if the company did do a lot of iterations and field testing.

  4. the downloaded video is only 205KB 🙁

  5. Aren’t those Dallas chips only rated to like 10 years or something when powered off?

    I know they incorporate a battery, NVRAM, and optionally the RTC, and are only guaranteed to keep time or data for around 10 years. Given it’s 30 years old, it might need changing…

    (The battery lasts longer when it’s on because the NVRAM and RTC wold use external power).

  6. Wow, 6502, what a legendary CPU! Apple II, Atari, Commodore 64, many other devices used it…

    Including the soviet “Agat”, a mostly incompatible replica of Apple II 🙂

    • The 6502. I missed that part in Dave’s teardown. When I was designing gauges and instrument clusters for VDO we had a custom uP that had a 6502 core. IIRC it was chosen because there weren’t any royalties associated with using it. When you make hundreds of thousands of something that makes a big difference. We were able to design
      custom internal I/O for the chip and the custom
      software libaries to go with it.

  7. Hi Dave,

    How about a tutorial on how to replace a Dallas chip? There has been lots of discussions on the form about them.

    – How to Remove: Without wiping the chip…
    – How to Reading Contents: Compatible programmers etc.
    – Selecting a replacement: Where to source replacements. An exact match or how to select compatible chips.
    – Re-Programing the replacement chip.
    – Replacement.

    Lots of traps for young players…

    And, You could even try some of the hacks for chopping to top off to add an external battery. 🙂

    • The Dallas chip is a battery backed SRAM chip. It is likely the contents are already gone because the battery is flat. In that case you can’t do anything.
      These you can just remove without fear of losing contents.

  8. Stupid question – where’s the manual?

  9. On the Dallas parts I know that the Conitec GALEP series of programmers can read those as I have done this many times for the ones used in TEK scopes. The programmer has a selection on the menus for the part. I have also done the newer DS12887 part and programmed it with data from the DS1287 part.

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