Editing Macintosh 512K

{{Infobox computer
| name         = Macintosh 512K
| image        = [[File:Macintosh128K.jpg|250px|frameless]]
| manufacturer = Apple Computer, Inc.
| type         = Personal computer
| release_date = September 1984
| discontinued = April 1986
| price        = US$3,195
| cpu          = Motorola 68000 @ 7.83 MHz
| memory       = 512 KB, soldered, not user-expandable
| rom          = 64 KB
| storage      = Internal single-sided 400 KB 3.5-inch floppy drive
| display      = 9-inch monochrome CRT, 512 × 342 pixels
| sound        = Four-voice, 8-bit D/A conversion, 22 kHz sampling
| ports        = DB-19 external floppy; DE-9 mouse; RJ-11 keyboard; 2 × RS-232/RS-422 serial (DE-9)
| power        = 105–125 V AC, 50–60 Hz, 60 W maximum
| dimensions   = 13.6 in H × 9.6 in W × 10.9 in D (34.5 × 24.4 × 27.6 cm)
| weight       = 16 lb 8 oz (7.5 kg)
| os           = System 1.1 – System 4.1
| predecessor  = [[Macintosh 128K]]
| successor    = [[Macintosh 512Ke]]
| codename     = Fat Mac
| model        = M0001W
}}
The '''Macintosh 512K''' was introduced in September 1984 as a [[Macintosh 128K]] with four times the memory. Everything else — the 68000 processor, the 64 KB ROM, the 9-inch monochrome screen and the single-sided 400 KB floppy drive — is the same, and Apple services the two machines from a single manual.<ref name="ss128">Apple Computer, ''Macintosh 128K/512K Service Source'' — Specifications, Take Apart and Adjustments chapters. Hosted on this wiki: [[:File:Macintosh 128k.512k.pdf]].</ref> It sold for US$3,195 and was nicknamed the Fat Mac.<ref name="ah">apple-history.com, ''Macintosh 512K'' (secondary source, used for the introduction price, codename and market dates).</ref>

The extra memory made the machine usable with the larger applications of the period, but it still had no internal hard disk, no SCSI port and no memory expansion: the RAM is soldered down. The [[Macintosh Plus]] addressed all three.

== Maintenance ==

The 512K is mechanically and electrically the same machine as the 128K, so its servicing, board layout and schematics are shared. See '''[[Macintosh 128K/512K General Maintenance]]''' and the [[Macintosh 128K]] page.

The machine contains a CRT; read [[CRT Discharge Procedure]] before opening the case.

== Specifications ==

Every figure in this table is from Apple's own specification pages for the 128K/512K.<ref name="ss128" />

<templatestyles src="Template:StyledTable/styles.css" />
{| class="wikitable styled-table" style="width:80%;"
! Item !! Specification
|-
| CPU || Motorola 68000, 7.83 MHz
|-
| RAM || 512 KB (the same manual covers the 128 KB machine)
|-
| ROM || 64 KB
|-
| PRAM || CMOS custom chip with 256 bytes of parameter memory, backed by a 4.5 V user-replaceable battery
|-
| Floppy drive || Internal single-sided 3.5-inch drive, 400 KB
|-
| External floppy || DB-19 connector
|-
| Mouse || DE-9 connector; mechanical tracking, optical shaft encoding at 3.54 pulses per mm
|-
| Keyboard || 58 keys, software mapped, RJ-11 connector
|-
| Serial || Two RS-232/RS-422 ports, DE-9 connectors
|-
| Sound || Four-voice, 8-bit digital/analogue conversion, 22 kHz sampling rate
|-
| Video || 9-inch diagonal screen, 512 × 342 bit-mapped display
|-
| Line voltage || 105–125 V AC, 50–60 Hz
|-
| Maximum power || 60 W
|-
| Dimensions || 13.6 × 9.6 × 10.9 in (34.5 × 24.4 × 27.6 cm)
|-
| Weight || 16 lb 8 oz (7.5 kg)
|}

== Memory ==

The 512 KB is soldered to the logic board. Apple offered no memory upgrade for this machine, and the RAM configuration is fixed in the logic that decodes it; period third-party boards that fitted Macintosh Plus ROMs and more memory existed, but they are logic board modifications rather than upgrades.<ref name="ah" /> The Macintosh Plus, which introduced the four 30-pin SIMM sockets used across the rest of the compact family, is documented on the [[Macintosh Plus Memory Upgrade Guide]].

== Power rails ==

Unlike the later compacts, this generation '''does''' have a published voltage adjustment. Apple's procedure connects the Macintosh voltage test cable (part number 077-0135) to the external floppy port and adjusts the regulator on the power/sweep board for '''11.90–12.75 V''' on the orange lead and '''4.85–5.15 V''' on the red lead; if both cannot be brought inside those windows the board is replaced.<ref name="ss128" /> The full procedure, with its warnings, is written up on [[Macintosh Plus General Maintenance]], which uses the same board family.

== Known board-level faults ==

''The Dead Mac Scrolls'' documents two faults that present as software problems:<ref name="dms">Larry Pina, ''The Dead Mac Scrolls'', Peachpit Press, 1992, "Early Macs" chapter. Hosted on this wiki: [[:File:The Dead Mac Scrolls 1992.pdf]].</ref>
* A 512K or 512Ke that resets a directly connected ImageWriter II on the printer port, or that never appears on an AppleTalk network, usually has a failed '''26LS30''' line driver at board location '''B6'''.
* On an original 128K analogue board that has been paired with an upgraded logic board, repeatable system errors that no other Macintosh shows are a low +5 V rail; the overvoltage reference diode (1N5349B) at '''CR18''' is the part to check.

== Related pages ==
* [[Macintosh 128K]]
* [[Macintosh 512Ke]]
* [[Macintosh Plus]]
* [[Macintosh 128K/512K General Maintenance]]
* [[Sad Mac Error Codes]] and the [[Sad Mac Decoder]]
* [[CRT Discharge Procedure]]

== References ==
<references />

[[Category:Apple Vintage Computers]]

{{Navbox-AppleVintage|state=collapsed}}