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.
load testing. this thing really needs a minimum load on the 5V rail otherwise the 12V rail misbehaves.
for the curious, the power supply schematic can be found here: http://www.appleiioz.com/AppleIIoz/Projects/Entries/2016/10/9_240V_Dyna_Comp_PSU_Circuit_Diagram_files/Dynacomp%20A2E%20Schematic.pdf. minor differences: it shows Q1 as a MOSFET when it is actually an NPN BJT.
made a little video adapter. this should work with my NEC Multisync (original).
well, we have video output! just need to get the drives connected, but i'll need to get my hands on some DB-19 cables first.
got a cable installed in the drive so now I'm bootstrapping ADTPro. it boots over the serial port, but then I write it to a disk to save time
thinking about how to upgrade the ROM 00 to ROM 01, i noticed that some (but not all) 27C1000 chips have the OE# input on pin 2 rather than on pin 24. this means that i could fit this 32 pin chip in the 28 pin ROM socket and let pins 1, 2, 31, and 32 hang off the end, and the remaining pins match 1:1!
bitsavers.orgthere are some cables coming your way tonight.
@bitsavers thank you!
Keith Kaisershot@tubetime yay! it lives!
europlus 
@tubetime Apple IIoz has lots of other good resources and schematics, and an Australian Apple II mailing list - check it out!
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.)
@cr1901 yes no MCU or controller. i think it's hysteretic. schematic link is in another toot but you can see how the LM339 on the secondary side handles the regulation and pulse width modulation...
@tubetime For my uni controls project I built a fan controller. I wanted it to use PWM, so I built an op-amp controller in positive feedback configuration. Unfortunately, I only had 3 pin fans at the time, so PWM meant that I lost all the tachometer pulses during the "off" part of the cycle. So I had to put that aside :(.
(There's a way to convert a 3-pin fan to a 4-pin one w/ a dedicated PWM pin, but I don't remember it offhand.)
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.
@tubetime I knew you’d fix it 🤓
Mira@tubetime That’s an usual failure mode, where the resistor is open but not obviously damaged. At least in my experience
Ivor Hewitt
Rue Mohr@tubetime mmm capacitor! 4.7uF 250V (I'm randomly guessing)
raweStress and heat cause wear and tear,
Reducing life, so design with care.
High ESR makes the current flow slow,
No charge to the gate, no power to show.
Lower that ESR, bring back the flow,
Reconnect the power, make it glow!
@RueNahcMohr i had to replace the output caps and a 1uf cap in the bootstrap circuit, but it was actually the 100k bootstrap resistor that was preventing it from coming up.
@tubetime how much would it cost to get enough to dunk.. {Rue looks out window and back} an small pickup truck...
Stinkie McPhee@RueNahcMohr @tubetime I'll split it with you. I need to dunk uhh... My old Jeep Cherokee and my Subaru Baja.
I have enough space to do it.
I have enough space to do it.
Roger Cheng@RueNahcMohr @tubetime Do you have enough e-waste salvaged parts to DIY a laser rust removal machine? I would love to see that. (Please don't blind yourself.)
The before/after footage of removing rust on this Renault Le Car is pretty amazing, even if not quite as magical as manufacturer promotion promised. That fender rust perforation still looks bad.
Finally his explanation of how it works didn't sound right to me, but he's presenting this as an end user so I'll tolerate some inaccuracy on underlying science and engineering.
How Laser Cleaning Deep Cleans 40 Years Of Rust On Cars | Insider Cars
Emily Velasco@RueNahcMohr @regorlas @tubetime start building one, rue. I feel like you have enough stuff to build almost anything
Martinius@tubetime I am not in the US and always use concentrated vinegar to remove rust. Is evapo-rust that much better?
@Martinius yeah it is quite effective and won't attack the base metal, unlike vinegar.
Guru_Meditation@tubetime Looking at Evaporust's instructions of use, they say "not fully immersed (...) can experienced etching at the water line", which could possibly suggest that at least a little base metal could be attacked. But the recommanded 24/48h treatment time also suggest it is rather weak/diluted, so a slow attack base. SDS from Radiospares also says it contains aliphatic acid, and acetic acid is an aliphatic acid. But website talks about selective chelation of iron oxyde + sulfur compound.
@tubetime And i've just read that molasses seems to contain some chelating agent working on rust, and is much cheaper, maybe something to explore...
Also, instructions say that a dry film of Evaporust can inhibit oxydation, but "upto 14 days" only. So some other kind of post-treatment should preferably be used to durably prevent rust to come back. What do you use for computer/electronic equipment parts?
Also, instructions say that a dry film of Evaporust can inhibit oxydation, but "upto 14 days" only. So some other kind of post-treatment should preferably be used to durably prevent rust to come back. What do you use for computer/electronic equipment parts?
Andrew Golding@tubetime what material did you use to do this?
@huronbikes the white one is UTR 8220. i forget the grey one.
Neil@tubetime The first time I changed one of those, I was surprised how soft and chewy those were.
Mark J. Blair@tubetime Mmmmm, Nilla wafer... 🤤
Bruno Philipe@tubetime don't these go epically when they go?
@tubetime Would be fun to take those outside well away from the house, put them on a step-up transformer and variac, and crank it until they pop
Andrew Zonenberg@tubetime am i the only one who reads that brand as "red imported fire ant"?
@tubetime 420 Rifa Madness!
plaes
Jencen - Please don't call me Derg@tubetime oooh. Some chonky ones there too! Those would go up a treat!
In my morning brain I have come up with the worst mens fragrance ever!
Parfum du RIFA!
jgeorge
Jonathan HendryThey're probably already dying but I wonder if younger RIFAs without cracks could be dipped in epoxy to prevent the usual moisture infiltration through cracked plastic.
@jonhendry it's probably easier to just replace or remove them.
Briala@tubetime "Some" :-D Looks like a IIGS?