Tube🌿Timei got a new Apple! 🧵
anyway, let's try and get this machine running. i have a funny feeling the video isn't going to work right...
sure enough, the machine chimes, but the video is blank. but i think i know what the problem is.
sure enough, there's no PRAM battery. these machines need that battery or you won't get video!
but where am i going to get a PRAM battery at this hour?
and we have working video! now for the most important question of the day: what version of Mac OS should i put on it?
i'm going to create a SCSI disk image for my SCSI2SD using BasiliskII and the instructions at https://www.savagetaylor.com/2019/12/19/how-ive-setup-the-scsi2sd-that-i-use-in-my-lc-475/
I was having trouble because I was putting the *volume* image into the SCSI2SD rather than the *disk* image. turns out partition tables are important lol
trying something else. unfortunately this didn't seem to work, I suspect the HFS partition needs to come before the ProDOS partitions.
well this explains why it was hanging. there's probably some setting on the SCSI2SD that's not exactly right.
turns out this hang was caused by the SCSI2SD firmware, which was uhh shamefully out of date. with the latest version it works and i can partition the drive!
it also turns out that MacOS wants to be the first data partition (i had the two ProDOS partitions first.) but it works now!
wow, it totally worked! is it an Apple IIe or is it a Performa 475? why not both!
i figured out how to change the startup sound to "Quack" which makes me think of the Quapple (my Apple II ISA card that i cloned a while back)
time to check the capacitors on the motherboard. there really aren't that many chips on it! I was also able to remove it without any tools. just bend some tabs and it slides right out.
i found a tech manual. this is a very clean design. most things are tidied up into the two big custom chips, MEMCjr and Prime Time.
heh, they even put the bus sizing features in this chip. motorola removed that in the '040 (the '030 had it) and it caused innumerable problems for 68k computer designers.
the Commodore folks solved this on their '040 Amiga CPU card by using a raft of ten (10) GALs, which burned a ton of power.
based on the pinout i think it's a 24C01 serial EEPROM, probably for a unique serial number or something.
yeah i'm wrong, this is a battery switchover circuit much like the MAX703. it provides voltage to the Cuda chip from the battery, and automatically switches to the 5V rail when power comes up.
I've 3D printed a drive bracket for the Performa. it's designed to hold the SCSI2SD.
it's a little loose but not a bad fit. I designed this based on photos of a real bracket, so the dimensions are probably slightly wrong
today's status: i'm having issues with the joystick port. the machine thinks it is pegged to the lower right even when it is centered.
the design is not an ADC. it uses a quad 555 timer with RC circuits composed of the external joystick resistance and 22nF capacitors. the Apple IIe just measures the time it takes to exceed the threshold.
it's just barely pegged at 250 or so. 2.8ms. the resistance is 87.8K, so this RC curve implies a capacitance of 68nF. that can't be correct.
inspecting the board reveals corrosion on the pins of an 'LS125, some of whose pins are wired into the joystick inputs (for some reason). i think the capacitor (already recapped C2) spilled electrolyte all over this area.
i removed the 'ls125. there was definitely a puddle of electrolyte underneath (it crackled and fizzed during desoldering). note that the potentiometer connection (red arrow) is right next to a pin tied to ground (blue arrow). electrolyte is conductive, so maybe it was creating a leakage current.
removing and cleaning the area helped quite a bit! it's not perfect so i think i have more cleaning to do.
i'm also thinking that the etched/oxidized solder joints in combination with the spilled electrolyte formed an electrolytic capacitor with about 45nF of capacitance. yeah that would do it.
so what does the 74ls125 do in this circuit? it's just discharging the timing capacitors. the NE558 also does this, so the 74ls125 is connected in parallel. I guess it... helps?
regardless i went and cleaned the board again more thoroughly, and it's working a lot better now. i'll replace the damaged 74ls125 later.
Karl Gutwin@tubetime Did you figure out what the ‘LS125 is doing there? I looked it up and guess it’s just a buffer. https://www.ti.com/lit/ds/symlink/sn54ls125a.pdf
@kgutwin it has the ability to pull the joystick lines low. no idea what this was for, none of the other apple II compatibles have it
William D. Jones@tubetime Ahhh, so IBM _wasn't_ the only company that used an RC circuit as an integrating ADC :'D!
Brian Danger Hicks@tubetime Sounds like an ADC to me.
George R. M. 🇩🇪🇺🇦@tubetime that's 343S0120, often found alongside the customized 68HC05 Apple calls Egret (Cuda in later models) used for ADB, housekeeping tasks, PRAM, reset (and NMI) management, etc. IIRC '0120 serves as a power monitor, switching the HC05 to battery power when system power is cut.
...as seen here on a 630 DOS/LC580 board.
Kevin Karhan 
James Carlson@tubetime This post suggests power management. https://68kmla.org/bb/index.php?threads/where-to-find-341s0851-c-1990-apple-lciii-boot-issues.37152/
Where to find 341S0851 (c) 1990 APPLE - LCIII boot issues
Hello All, Anybody knows where to find this MCU which has Apple programming on it? I am working on a very tired board which suffered from battery damage etc. - no boot of course. Aside from all sorts of issues and a need to replace dead CPU (yup-it looks like) it probably has bad 341S0851 chip...
Tevruden Dawnspear@tubetime I feel like that's the spiritual successor of the SE's BBU which turned a half dozen or so PALs into a single chip
@tubetime I wonder why a similar situation didn't cause problems in PC land when going from 8088 to 286 bus (and again from 286 to 386)? 8-bit ISA works (mostly) fine on newer machines. I wonder if this is a port-mapped I/O accommodation?
I remember hearing- emphasis on _only hearing_- the 286 has some _slight_ incompatibilities when talking to 8-bit devices with an I/O port at an odd address. But most cards in practice didn't run into this.
@cr1901 hmm, i don't know. intel was all about backwards compatibility, so probably the CPU handled it automatically.
Elosha@tubetime Really clean! I love that they put legacy MOS 8bit VIA clones on chip, just like PC people had Intel 8bit chip clones in their Chipsets ☺️
John Carlsen@tubetime copyright 1982 on the ROM--wow!
Was this unit among the first sold in 1984?
Was this unit among the first sold in 1984?
@johnlogic no this is a later mac from 1993
@tubetime thanks!
I think Apple added the expansion port on the Mac SE; I recall working on a prototype add-on for that port in 1989. I think the port used a conventional DIN 41612 connector; this one looks like a newer, extended version.
@tubetime Definitely a #Macintosh #mainboard:
I've not seen and #PDS "slot" sockets anywhere else...
Nate Martin@tubetime I miss that control panel....
@natemartinsf it's super clean! also dang you're on mastodon too, i will follow you asap
@tubetime I heard all the cool kids are here now!
Travis Geiselbrecht@tubetime Oooh that looks fun. Alas all I have in the classic mac world is a Mac SE with no slots.
But I do have a Apple IIe, so I guess that's second best.
But I do have a Apple IIe, so I guess that's second best.
Kevix (he/him) :debian:@tubetime
I'm on a apple ii group on facebook and in the 90s I had a Performa 475 I think but never had the apple II card. There is a mastodon apple program I think?
I'm on a apple ii group on facebook and in the 90s I had a Performa 475 I think but never had the apple II card. There is a mastodon apple program I think?