I had an encounter with a button, and now I want to share my findings with the community. I did not have to replace my button, so the information below is my best effort to collect it, but some of it is unverified...
The Lisa is probably the 1st computer that could be turned on via push button, and shut down programmatically, from a "Power off" menu in the operating system, or by pushing the power button again. Nowadays all computers have adopted it...
The Lisa power-on button is located on the front panel, under the drives cage.To remove it (for repairs and whatnot), you will need to remove the top cover (for which you need to unscrew it from its back, for which you need to remove the electronics cage and power supply), the front cover, and the drive cage. The button is soldered onto a small PCB board (part number 820-4020-B) , along with the keyboard connector. The board is held to the bottom chassis with two screws.
The button is made by Honeywell, model AML21CBA3AA (based on the post at
https://68kmla.org/bb/index.php?threads/chasing-down-lisa-error-52-cop-i-o-board-etc.46971/). It can still be found at major electronics retailers, and costs around $40. Yikes. Do a comparison shopping at
https://octopart.com/search?q=AML21CBA3AA¤cy=USD&specs=0 , make sure to click "Show all" to see all offerings. It MAY be possible that models AML21CBA3AB (a 2-pole button) and AML21CBA3AC (a 4-pole button) also fit and work, see the picture of the PCB below; but they are even more expensive. AML21CBA3AB is a single "push" button (aka "momentary action") vs other models that are an alternating button (push on / push off). Also, note that the pins on the back are thin (meant to be soldered on a PCB board); there are other models that have thicker pins with a hole in them (to solder wires to them); they will not fit on the PCB board unless you hack it.
The button has two metal brackets that surround it; they seem to serve no purpose on the Lisa; they were intended by the manufacturer to affix the button inside square openings; On the Lisa, the button is not attached to the hole where it sits; it's held in the right place by its soldered legs.
There is a small replaceable light bulb inside the button that illuminates it when the Lisa is on.To replace the bulb, if needed:
0. You may be able to do ths without opening the Lisa (without removing the power button PCB board)
1. pry the front white plastic button piece : carefully insert a sharp tool directly below it, then pry the plastic piece towards you, until it is loose from the bottom, then repeat on the top, until it comes out.
2. you will see the bulb inside the button. There is a tiny metal tab below it. Pull it (with a small flat screwdriver), and it will eject the bulb.
3. The bulb appears to be a "#79 Bulb" (you can google it) : it's a T 13/4 bulb (aka T1.75), which means that its diameter is 1.75 times x 1/8 of an inch, which comes to 0.22 inches diameter = 5.5mm diameter; the voltage is 6V (but the Lisa powers it with 5V). The socket is a rectangle piece of glass with dimensions 2.1mm wide x 4.9mm high; the total bulb height is about 17 mm. Your local auto parts store may also have it.
4. Insert the new bulb the same way the old came out (the bulb socket should be oriented horizontally). Try not inserting it all the way in (let the white plastic push button above it push it in as deep as needed). This is because the bulb socket seems to be wider at its bottom, and it may not make good contact.
5. Replace the white plastic cover piece. It has two small slots, on two opposite sides; these slots must be oriented to be above and below the plastic piece. Just push the plastic in place and wiggle until it clicks into place.
6. Note: brand new buttons do not come with a bulb; use the old one, or buy it separately.
Wiring:
A 10-pin ribbon cable connects the IDC10 connector on the Power switch board to the first 8 pins (4 top pins and 4 bottom pins, the rest 2 wires are unused) of the J1 connector; this is the horizontal connector where the bottom motherboard plugs into when the electronics cage is inserted into the Lisa.
- The "Power switch" signal is on pin 54 (this is the 4th pin on top left side) of the J1 connector. It goes through the bottom motherboard to pin 119 on the I/O slot. From there, it reaches the I/O board, where it goes through a TTL "buffer" to the COPS chip. It seems that the buffer and the COPS chip are always powered on (even when the Lisa is off) through the "5V Standby" from the power supply. Upon pushing the power switch, the COPS sends an "ON" +5V signal to the power supply, and the Lisa turns on. The Lisa 2/5 and 2/10 I/O boards are identical when it comes to this functionality.
- The "Keyboard" signal is on pin 58 (this is the 2nd pin on top left side) of the J1 connector. It goes through the bottom motherboard to pin 88 on the I/O slot, and from there to the COPS chip on the I/O board.
It seems that all Lisa models are the same in regards to the power button.
See the attached photos for more info.
Is your Lisa turning on as soon as you plug the power cord? And then it shows an I/O Error 52? This is because your power button has a mechanical failure and is stuck in "always on" position. Pry it open (without desoldering it), fiddle with it, see if you can fix it, and, if no luck, desolder and replace it with a new one. Or hack it: use a flat screwdriver to touch the button's contacts to turn the Lisa on/off. Or run two wires outside of the Lisa and hook up your favorite button. Make sure to wear your white hacker hat, and brag to your wife.
Enjoy.
