Tube🌿TimeI got a new computer!
these RIFA capacitors will need to come out. they're just waiting to go up in smoke at this point.
the feet come off easily on these drives. maybe I'll try printing replacements with TPU.
something's not right! actually it's very common for stuff from ewaste to be missing any captive cables. those get cut off for copper scrap and to prevent items from tangling. engineers: please don't design products with captive cables!
going back to the IIgs enclosure, i'm soaking it in Evapo-rust to clean it up. i don't have enough to dunk the whole thing...
I hate working on AC power supplies. this one seems to have issues with the bootstrap.
welp, the bootstrap resistor is open circuit! it should be 100K. the main power transistor (NPN BJT) is in the background, a Motorola 20595. pin 1 is the base, 2 is the collector, and 3 is the emitter.
well that was the problem. it powers up and provides 5V into a 1A load. (the big ceramic resistor is something I bodged as a way to discharge the input reservoir capacitors). it chirps pretty loudly during power on, not sure what's up with that.
this power supply needs an initial "kick" to get voltages to appear in a bunch of places that bias up the oscillator and power transistor drive circuit. the 100k resistor (circled) provides that.
William D. Jones@tubetime This is an SMPS without a microcontroller or dedicated IC to handle the switching?
(Can't tell if the inductors on the right are supposed to have sine wave or square wave output.
Transformers coupling a square wave always bugged me b/c transformers only work for signals where the derivative is nonzero. But what's the derivative of a square wave? Well it's not a nice looking signal :P.)
Marsh Ray@cr1901 @tubetime A square wave is just a sine wave with a lot of energy in odd harmonics decreasing in amplitude.
I’m thinking as the primary is putting energy in, the secondary should be taking it right back out. Ideally the amp-turns cancel. So it’s that lowest, fundamental frequency that dictates the peak flux the core needs to handle. Sine waves distort at core saturation too.
So it’s more the lowness of the frequency than the squareness of the wave that’s the challenge.
@marshray @tubetime TIL about amp-turn (shorter way of saying "conservation of energy must hold"): https://en.wikipedia.org/wiki/Ampere-turn
> Sine waves distort at core saturation too.
Indeed, but sine waves are much more pleasant to reason about compared to square waves, at least before nonlinearities kick in :P.