Monthly Archives: March 2016

Apple II S/N 5025 (continued)

After last month’s post about A2S1-5025, I received several requests for photos of specific areas of the machine that were not visible in the first set of pictures. Here you go:

This is the keyboard, removed from the case.

Rev 0 Keyboard (second version)

Rev 0 Keyboard (second version)

Bottom of the keyboard.

Apple II Rev 0 keyboard, second version - from the bottom.

Apple II Rev 0 keyboard, second version – from the bottom.

Apple part number 01-0425-01 is described in the Apple II/II-Plus Level II Service Manual (1981, Pre-Release Version, available in PDF format here – do a text search for “keyboard varieties” in the file) as “The first Apple keyboard,” but it is not. The early revision 0’s shipped with 01-0341-01, an example of which can be viewed here.

As with the Apple II board itself, the early days of production saw the keyboard undergo a number of changes more evolutionary than revolutionary. The circuit board was made shorter and wider to better fit the case, with the silver leaf plates formerly used to secure the keyboard to the plastic sacrificed to make room for the reconfigured electronics. The silk-screened Apple part number was moved from the lower right to left…

Apple II keyboard second version (01-0425-01)

Apple II keyboard second version (01-0425-01)

The encoder chip and associated electronics were migrated to the lower right…

Apple II Rev 0 keyboard encoder chip

Apple II Rev 0 keyboard encoder chip

These long, threaded, brass posts lined up with the spacers on the PCB to provide a mounting system.

Threaded brass posts affix the keyboard to the case.

Threaded brass posts affix the keyboard to the case.

The mounting set up is reinforced with these hollow spacers that also align the keyboard assembly on the brass posts.

Hollow spacers provide guides for the posts and reinforce the mounting.

Hollow spacers provide guides for the posts and reinforce the mounting.

Here’s the upper shell, removed from the base pan and keyboard.

Apple II Rev 0 case - upper shell

Apple II Rev 0 case – upper shell

Close up of the black nylon “velcro” lid fastener pad.

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When trying to determine whether an Apple II is a revision 0 or some later production model, there are a few identifying markers on the motherboard that can quickly be verified. One of the indicators easiest to identify is the presence (or lack) of the color killer circuit, which includes a transistor visible on the PCB in the area to the right of the CPU, between rows F and H (there’s no row G), like so:

Color-kill circuit transistor.

Color-kill circuit transistor.

This circuit was added to production beginning with the revision 1 boards so it’s simple math: no transistor means the board is a revision 0.

All revision 0 boards, and only revision 0 boards, lack the color kill circuit. (I, on the other hand, lack grammatical skills apparently.)

All revision 0 boards, and only revision 0 boards, lack the color kill circuit. (I, on the other hand, lack grammatical skills apparently.)

Another “dead giveaway” that you’re looking at revision 0 board can be found under the 6502 chip. Or rather, not found. All Apple II boards beginning with the revision 1 run were assigned a part number which, early on, could be found by taking a peek under the processor. As an example, here’s what you see when you pry up the CPU on a rev 0 board, with the revision 4 Apple II Plus below it.

Rev 0. No part number under the CPU.

Rev 0. No part number under the CPU.

Apple II Plus rev 4 part number under the CPU.

Apple II Plus rev 4 part number under the CPU.

These memory select jumper blocks allowed users to upgrade their memory easily. Simply plug-in your new DRAMs and insert the appropriate jumper blocks to let the computer know how much memory it had to work with. The presence of these, while an indicator that you are looking at an early Apple II board, doesn’t guarantee a revision 0. Later boards shipped with them soldered in place and at some point they were removed altogether.

Revision 0 memory blocks, not soldered.

Revision 0 memory blocks, not soldered.

This is one that often gets missed in auction photos on eBay because of the awkward position you have to hold your phone in to get a clear shot, but a surefire indicator is the copyright date that appears just above the system ROMs and below the Apple Computer logo. Only revision 0’s are marked ‘1977’; every thing after that stamped with a 1978 copyright (or later.)

Only Revision 0 boards are (c) 1977.

Only Revision 0 boards are (c) 1977.

Someone asked for a shot of the underside of the 6502, so here you go. I assume “PHIL.” means it was manufactured in the Philippines. No idea what the other text might mean.

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I’ve got a few more areas to cover, but that’s probably enough for now. I’ll knock the rest out in a third post next week.