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Oct 12, 2021 19 tweets 5 min read Read on X
oops I got another computer. this one is a PCjr! Image
not a typical PC under the hood. Image
it's dustier than a crypt inside! Image
the power supply (far left) seems to require low-voltage AC. there must be an external power transformer. Image
the motherboard, sans dust. there's still some gunk left, so you know what's coming up next... Image
ColorCoral! it's soon going to turn a nasty shade of grey. Image
bleh Image
ooh a quad 555 timer. must be for the joystick port. Image
the infrared receiver (for the keyboard) is under the shield. Image
washed and dried the case. I had a hard time getting the front off, it's press fit into those little holes on the front. mine was already loose, otherwise I wouldn't have done it Image
I guess they cheaped out and didn't get fasteners Image
which is odd because right here they have a brass insert Image
putting it all back together Image
the pins on this 0.1" header are round instead of square 🤔 Image
JJLKLPTVMDSCPA. IO
what does it all mean Image
this computer has no D-sub connectors. just 0.1" headers. to save money? perhaps. but IBM also sold the RT PC, a high end workstation, with the same sort of connectors. Image
i wonder if i should design a Snark Barker sidecar for the PCjr. obviously it would be called the "Snark Barker Snide Car"
finally got around to powering it up, and it works! Image
i don't have the external power brick so i just used my bench supply. oh yeah i have no keyboard 😂 Image

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More from @TubeTimeUS

Jun 13, 2023
here's a weird object! it's some kind of foot pedal with an IBM logo. is it for a sewing machine? electronic synthesizer? what do you think? 🧵 Image
it's got a cursed connector! what IS that? Image
amazingly enough, I found something with the mating connector on it! but what is it? Image
Read 24 tweets
Jan 11, 2023
hey so remember the world's cutest oscilloscope i picked up last year? i think it's time to fix the probe socket issue.
i printed a new panel insert that has two BNC sockets on it (the original probes would have had captive cables)
the tricky part is that this oscilloscope has a 333K ohm input impedance instead of 1M like umm every other scope on the planet. fortunately someone designed a little conversion circuit...
Read 11 tweets
Jan 5, 2023
in honor of Sim Wong Hoo, here's a quick historical review of the Sound Blaster! 🧵
but first we have to go back to their first sound card, the Creative Music System from 1987. (image credit: Bratgoul on Wikipedia)
this card has some special "CMS-301" chips. if you peel back the sticker, they have had their top marks removed. they're actually SAA1099 synthesizer chips made by Philips. Creative wrote music composition software for musicians on the PC.
Read 23 tweets
Dec 31, 2022
Tube Time: a 2022 retrospective 🧵
(and stuff you might have missed!) Image
starting things off in january, i found a tube of super old 555 timer chips! i also decapped one of them.
i also started fixing up an old HP 150 computer. it's not PC compatible but it runs MS-DOS--how odd!
Read 65 tweets
Dec 29, 2022
today's mini project: fixing this Radius Thunder IV GX daughtercard. it looks fine, but... 🧵 Image
one of the chips has some broken pins! Image
looks like two of the pins got mashed and broke right at the plastic package. Image
Read 11 tweets
Dec 8, 2022
on the bench of healing tonight: my coffee grinder which decided to bite the dust. Image
symptoms: i push the start button and the motor just bumps a little bit and stops.
how to take it apart? hmm, i bet there are screws under the rubber feet. Image
Read 23 tweets

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