Gregory's Serverthis is neat, the front panel has an indicator LED that can be configured to light up when the speaker makes a noise.
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162 comments
 @tubetime I'm not sure, but I think your sheet size is a tad bit too small for your schematic 
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@tubetime Huh? On a power supply board? What sub-circuit are these resistors part of? @attilakinali there are 7 of them. they trim the output voltages and a few other parameters @tubetime interesting. I would have thought that 1% resistors would do the job for the voltage feedback of something like a computer. Any idea why they need this level of accuracy? @attilakinali 1% is indeed fine for this. but they probably thought doing it this way was some sort of competitive advantage lol  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! want to stare at the schematic yourself? i've put it on GitHub. https://github.com/schlae/Thinkpad700CPower
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 I just checked and (thankfully) CHM doesn't have one. They actually have almost no ThinkPads in the collection. I have nightmares about how many early 90s machines in the collection have pcb rot. @tubetime I had totally forgotten about active vs passive matrix displays! The minute I saw an IBM active matrix LCD, I knew the end was nigh for the CRT. It was amazing for its time. @tubetime Active matrix, man. A million psychedelic colors... I bet it looks crispy in the dark. @tubetime The single strip of Scotch tape in the middle is a nice touch.  @tubetime Did you have to make your own contacts of could you reuse something else? @tubetime Others have speculated in the past that IBM used Nextel Suede coating. https://www.nextel-coating.com/produkt/nextel-suede-coating-3101-90fh-11-black/?lang=en&v=3a52f3c22ed6. I am not sure if that info is correct. Difficult to get in the USA and $$$. I know folks who may have very limited quantities (used on aircraft instrument panels), may be the wrong color or variant.  @jonhendry by shining a flashlight through the board and looking at the shadow of the trace. if it is more distant or fuzzy, then it's on the opposite side of the aluminum core  @tubetime I'm guessing they trimmed to tune the system as a whole, not just the single resistor value? @tubetime My first job out of school was doing fpga stuff at a company that did laser trimming. It was wild. They used analog circuits to drive the galvos which had the mirrors. If the circuitry was off by a bit, you could see the “ringing” of the circuits in the right angle cuts (instead of an angle you’d see a little degrading sine wave). I’m still convinced analog EE’s are wizards. |
ok it stopped working again, something with the power board. i'm doing more reverse engineering. this is barely half the board!