Apple II Schematics
The file hosted here is Apple's Addendum to the Apple II Reference Manual, 12 pages: two pages of text followed by ten schematic sheets of the Apple II main logic board. Apple issued it when the main board was redesigned to reduce electromagnetic interference. The text describes changes that affect anyone working on a revised board from the original Apple II Reference Manual.
What the addendum says
[edit | edit source]- Identifying the board: "You will know you have a new main board by looking at the white F on the far left side of the board. You'll see there this nine digit number 820-0044-xx, where xx is the revision level."
- The new board has no RAM configuration blocks, so all RAM ICs must be 16K-bit devices. All the RAM is inside the white-outlined box on the board.
- The IC that controlled the configuration blocks on older boards "is no longer there. It was formerly in the E2 position on the Apple board (in the row labeled E, the second IC from the left of the board) and was marked 74LS139."
- The character generator ROM sits next to the keyboard socket. The new 2316B ROM has more space than the former 2513, so more than one character set is possible, and the 2316B can be replaced with a 2716 EPROM programmed with a custom character set.
- The colour killer, which damps the colour burst in text mode, has an added cutout: the burst is cut off in the logic before it reaches the tank circuit, giving clean black-and-white text even on a colour monitor with a sensitive burst detector.
- "The +5V and ground bus on the rear of the board have been interchanged so that the +5V bus is on the top of the board and the ground is on the bottom. A grounding bar has been added under the board to ensure electrical contact between the board and the metal baseplate. Additional filters have been added to further reduce the EMI emission levels."
The last change matters when probing: on a revised board, the rear bus position that was ground on an older board is +5 V.
The schematics
[edit | edit source]Ten sheets in Apple's drawing style. Apple II integrated circuits are identified by board grid position, a row letter and a column number such as B11, C11 or C14, not by a sequential U-number; the part type is named separately on the drawing. One sheet is headed MAIN LOGIC BOARD and carries a US patent notice. The sheets are image-only scans with no text layer.
What this document does not contain
[edit | edit source]No parts list of passive components and no bill of materials; resistor and capacitor values appear only where a drawing carries them. No troubleshooting section, specification table or disassembly procedure. Apple's service procedures and parts numbers for the Apple II and II Plus are in File:Apple II and II Plus Technical Procedures.pdf.
Pages that cite this document
[edit | edit source]- Apple II: the RFI board and its 820-0044 number.
- Apple II Reference Manual: the manual this is an addendum to.
Download: Apple II Schematic.pdf