@tubetime@mastodon.social
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tubetime

@tubetime@mastodon.social

vintage computers, tubes, the MOnSter6502, cross-sectioned electronic parts, capacitors, and other detritus. coauthor of http://nostarch.com/open-circuits

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tubetime, to random
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this is a Nuvistor! it's a super-advanced vacuum tube that could have beaten the transistor.

tubetime,
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in 1959, RCA took their tube-making expertise and made this micro miniature tube almost as small as a 1950s transistor

tubetime,
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RCA developed all new equipment to make it. this machine seals a batch of Nuvistors automatically!

tubetime,
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in the 1950s, tubes still had advantages over transistors -- they even lasted longer!

tubetime,
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so how did they miniaturize the Nuvistor? time to cut one in half. check out the cross section!

tubetime,
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i'd annotate my photo, but RCA published a really nice cutaway diagram, so i will show you that instead.

tubetime,
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Nuvistors found their way into some high end applications but transistors surpassed them in a few years, and they just faded away.

tubetime,
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fascinating to imagine an alternate reality where transistors never worked and people figured out how to miniaturize vacuum tubes, etching arrays of them on metal wafers and building computers. In fact, they could even have built the entire Internet using a series of tubes.

tubetime, to random
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a new arrival: a Thinkpad 700C! words cannot convey how uhh sticky the soft-touch paint has gotten.

tubetime,
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i should mention how i fixed the very stiff hinges in the Thinkpad 700C. i supported the hinge and hit the shaft with a hammer (red arrow). this backed out the locking washer and reduced the pressure on the hinge stack, and therefore the friction.

tubetime,
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I've installed a new coin cell. yes I soldered wires directly to the cell 😬

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tubetime,
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this is neat, the front panel has an indicator LED that can be configured to light up when the speaker makes a noise.

tubetime,
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ok it stopped working again, something with the power board. i'm doing more reverse engineering. this is barely half the board!

tubetime,
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this is fascinating: the power board has several laser trimmed resistors (sure, pretty common) but these have been laser trimmed AFTER being soldered onto the board!

tubetime,
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now i am repairing some more vias. the capacitors leaked and etched out a bunch of vias. this one needs to be connected on layer 2, so i had to remove some copper pour and FR4 to expose the trace.

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tubetime,
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ok i have a theory about why this was failing. symptoms: randomly the computer would shut off and pull a ton of current...

  1. crowbar circuit fires. it can fire due to a rail going overvoltage...

  2. a buck converter's MOSFET wasn't switching properly...

  3. oh look this diode wasn't connected anymore due to a bad via!

tubetime,
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want to stare at the schematic yourself? i've put it on GitHub. https://github.com/schlae/Thinkpad700CPower

tubetime,
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it's working. that was a big step forward!

tubetime,
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it's really too bad the soft touch paint gets sticky. black? not quite -- it's got flecks of blue pearlescent pigment!

tubetime,
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i would also like to comment that the 640x480 color LCD screen is utterly fantastic for 1992. it's active matrix and beats the crap out of the more common passive screens of the time

tubetime,
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cracking open the battery. it's ultrasonically welded shut. the trick is to find a weak point and start wedging it open.

tubetime,
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then you just work your way around the seam, cracking it apart.

tubetime,
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tada! looks like 18 cells total. maybe 2/3 AA sized?

tubetime,
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it died again. the problem was this via. I dug out the FR4 and reconnected it to the trace on layer 2.

tubetime,
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back in business. for now anyway. 😅

tubetime,
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I 3D printed a new power connector. the strain relief is printed using TPU.

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