Keyboard activated power supply help - Page 1
Forum section: electronics / projects

author: TRS-90
author_rank: Regular Contributor
timestamp: April 28, 2016, 01:40:38 am
content: I don't know if I got the title correct so if I did not I apologize.I have an old apple macintosh power supply that uses a special keyboard key to turn the power supply on.BUT I would like the power supply to be on as soon as I flip the switch on the back of the machine.How would I go about doing this or is there even a way to bypass that activation signal.Thanks in advance

author: jeroen79
author_rank: Frequent Contributor
timestamp: April 28, 2016, 02:03:38 am
content: It depends on how this works.My guess is that it has a standby powersupply that keeps the keyboard and a controller on the mainboard alive.The controller then turns on the main PSU once it receives the required input from the keyboard.You could program a microcontroller to send this input to the controller or the PSU once after it is powered on by the standby PSU.How is the main PSU turned on?Is there a relay?Do you know the specific type and version of the computer?

author: TRS-90
author_rank: Regular Contributor
timestamp: April 28, 2016, 02:13:06 am
content: I didn't see a relay nor can I hear one.The computer is a Macintosh Performa 577 dating from around 1993/94 (it is an all in one type computer)The CRT gets power but the computer part does not.I would like the power supply to always be on when there is power going to it without using any external devices.

author: packetbob
author_rank: Contributor
timestamp: April 28, 2016, 02:26:59 am
content: I ran several Mac based BBS back in the day on IIci's and wanted to run them headless (no kybd/mouse/monitor) using Timbuktu (was like PCAnywhere) to remotely admin them.As I recall (and I have to confirm) that the keyboard communicates over the ADB (Apple Desktop Bus) which used a MiniDin connector (S-Video cables could be used in a pinch) however the keyboard power button switched one of the pins that wasn't used by the ADB. I think I built a little box with a push button on the end of a hacked S-Video cable to be able to power it up without the keyword....I can`t remember if keeping the contacts closed made it always power up after a power failure or not but I recall it was something like that...Mind you this was 20 or so years ago.... I may be remembering it wrong......

author: TRS-90
author_rank: Regular Contributor
timestamp: April 28, 2016, 02:33:01 am
content: But how do that without the logic board.I attaching a video game console to the CRT for a display and would like to use the 5 and 12 volts from the logic board harness.Already have most of the video part covered just need the power supply pin on the edge connector

author: packetbob
author_rank: Contributor
timestamp: April 28, 2016, 02:38:10 am
content: the ADB connector was probably on the motherboard so the power pin from it must get routed to the power supply connector.. think you just need to connect that pin to +5 to power up the PS...

author: packetbob
author_rank: Contributor
timestamp: April 28, 2016, 03:06:32 am
content: Found this snippet of a IIci schematic..Looks like J14 is the power supply connector to the motherboard...Connecting pin 9 on this to pin 10 should turn on the power supply....YMMV

author: helius
author_rank: Super Contributor
timestamp: April 28, 2016, 04:23:33 am
content: OP: How many threads do you need to ask the same questions over and over?packetbob: The power-on circuit was different on the different generations of machine, of which there were several. None of it matters, because the OP is talking about forcing the PSU on directly, as thousands of DIYers do by putting paperclips into ATX power supplies. The entire circuit in that schematic is then redundant. All he needs to do is put a suitable resistor (looks like 220R would work) in between "continuous +5V" and "PS On", but he doesn't know where those pins are (they are not in a connector remotely like the one used in the IIci).