Dotson ELF II system, mods

Most recent revision of this page Sept 19 2024(c) Herb Johnson. This Web page is preliminary, work in progress. I describe this elf II, when I obtained it, at this linked Web page.

On this Web page, I'm figuring out the mods made by Will Dotson, the original owner of this Elf II. To do so, I'll need to trace out all the extra wires, to various added connectors. There's also a small hand-wired PC perfboard under the Elf II. When the wires are identified and the connections traced (as sketched), then I can draw a series of schematics to combine the tracings. Finally I'll integrate the schematics with the original Elf II schematic. - Herb Johnson

Overview

top of Elf II boards removed
Elf II board layout, component side, note small perfboard
back of Elf II, note connectors and switches
Elf II schematic, some wiring marked by Dotson
Here's a rough list of ICs on the Elf II board.

closeups of mods to backplane

Note use of colored wires. Wire descriptions are major color / minor color, as a white wire with yellow marks is "white/yellow".

Elf II modded backplane (solder side)
small logic board on backplane
back of small logic board
- hand wired with enamel-coated wires, possibly "slit-n-wrap"?
wiring around small board
wiring on slots
wiring in corner to a pair of nuts, attached to a battery
... and here's the battery, plastic unwrapped

tracing wires around; progress

tracing connector wiring
tracing near elfII IC's
tracing memory protect switch
- hex nuts pair on far left, wired to memory backup battery, in plastic pouch
tracing wires on slots
tracing colored wires from small logic board
- pay attention to orientation of board IC's
tracing as above, add IC pin numbers
tracing IC wiring under small logic board
- pay attention to orientation of board IC's

schematics of small board under elfII; final Sept 7 2024

schematic of small board and wires, completed
Dotson says the resistors are to create oscillators, different values different frequencies
connecting wires to small board, tracing completed

Dotson: "From your wiring diagram of the small logic board under the Elf, I can see that there are 2 resistors connected to pins on the 4093 Schmidt trigger chip. These are probably oscillators, but of not particularly accurate or specific frequencies. I remember using this kind of circuit when I wanted a quick and dirty oscillator."

My most-current description of the small logic board's operation. I think it disables /MREAD on the backplane for addresses C000H to FFFFH (A15 and A14 high). I'll need to run this conclusion past some people to see. - Herb

Herb Johnson
New Jersey, USA
follow this link to email me @ my email address