jbr@key.COM (Jeff Rubin) (03/02/90)
It was reported by several people that it is unsafe to plug and unplug ADB devices when the Mac is powered on. Some have even reported blown chips on the motherboard that were attributed to this type of manipulation. I'm not sure which machines my question pertains to, so I will phrase it in terms of my Mac IIcx. The keyboard (Apple extended) has a button with a triangle on it that I use to turn the power on. Since the keyboard is an ADB device, does the power-on mechanism use the ADB? If so, does this imply that ADB has power even when the rest of the machine doesn't? Does that mean that it is not safe (just as unsafe?) to plug/unplug ADB devices when the power is off? Do I have to pull the plug from the wall before it is safe? Is there a big capacitor on the power bus? How long do I have to wait after I pull the plug from the wall? Inquiring minds want to know ... and I do too. ------------------------------------------------------------ Jeff Rubin ...!amdahl!key!jbr
d88-jwa@nada.kth.se (Jon Watte) (03/02/90)
In article <1494@key.COM> jbr@hongkong.key.COM (Jeff Rubin) writes: >phrase it in terms of my Mac IIcx. The keyboard (Apple extended) >has a button with a triangle on it that I use to turn the power >on. Since the keyboard is an ADB device, does the power-on >mechanism use the ADB? If so, does this imply that ADB has power The power-on mechanism is separate from the bus mechanism. There is no key code for the pover-on key, the only thing it does is sinking pin 2 on the bus (marked reserved or n/c) when pressed. Note: the power to sense this comes from the battery, therefore it's no wise idea to leave the key depressed for extended time. h+ -- --- Stay alert ! - Trust no one ! - Keep your laser handy ! --- h+@nada.kth.se == h+@proxxi.se == Jon Watte longer .sig available on request
davide@cs.qmw.ac.uk (David Edmondson) (03/02/90)
In article <1494@key.COM> jbr@hongkong.key.COM (Jeff Rubin) writes: > >It was reported by several people that it is unsafe to plug and >unplug ADB devices when the Mac is powered on. Some have even >reported blown chips on the motherboard that were attributed to >this type of manipulation. > >I'm not sure which machines my question pertains to, so I will >phrase it in terms of my Mac IIcx. The keyboard (Apple extended) >has a button with a triangle on it that I use to turn the power >on. Since the keyboard is an ADB device, does the power-on >mechanism use the ADB? If so, does this imply that ADB has power >even when the rest of the machine doesn't? Does that mean that it >is not safe (just as unsafe?) to plug/unplug ADB devices when the >power is off? Do I have to pull the plug from the wall before it No. In the MacII the fuse that blows is for the +5V supply, the power on line is a different circuit which uses the internal batteries to wake up the main power supply (this is why Modular Macs will not start if they have a flat battery). So the machine must be shutdown but you can leave it plugged in. I would dearly like to know if this problem has been fixed in later models, our students seem to have a habit of yanking out keyboard cables on IIcx but none of them has killed the ADB (yet). See Apple Macintosh Family Hardware Reference Guide Chapters 19 and 23. -- David Edmondson UUCP: davide@qmw-cs.uucp or ...seismo!mcvax!ukc!qmw-cs!davide ARPA: davide%cs.qmw@nsfnet-relay.ac.uk Post: Dept of Computer Science JANET: davide@uk.ac.qmw.cs Queen Mary and Westfield College Applelink: UK0087 University of London Mile End Road London E1 4NS Voice: +44 1 975 5250 England
david@wolfen.cc.uow.oz (David E. A. Wilson) (03/03/90)
In article <1494@key.COM> jbr@hongkong.key.COM (Jeff Rubin) writes: >phrase it in terms of my Mac IIcx. The keyboard (Apple extended) >has a button with a triangle on it that I use to turn the power >on. Since the keyboard is an ADB device, does the power-on >mechanism use the ADB? If so, does this imply that ADB has power >even when the rest of the machine doesn't? Does that mean that it >is not safe (just as unsafe?) to plug/unplug ADB devices when the >power is off? Do I have to pull the plug from the wall before it >is safe? Is there a big capacitor on the power bus? How long do >I have to wait after I pull the plug from the wall? At least with a Mac II, if you unplug the power lead and then hit the <| button the machine starts to power up and then comes to a halt (even the hard disk starts to spin up & then stops). From this I deduce that either the power supply capacitors or the motherboard batteries supply power to the keyboard and enough circuitry to turn on the power supply to the rest of the Mac.
psu@mtuni.ATT.COM (Paul Siu) (03/06/90)
In article <1738@sequent.cs.qmw.ac.uk> davide@cs.qmc.ac.uk (David Edmondson) writes: >In article <1494@key.COM> jbr@hongkong.key.COM (Jeff Rubin) writes: >> >>It was reported by several people that it is unsafe to plug and >>unplug ADB devices when the Mac is powered on. Some have even >>reported blown chips on the motherboard that were attributed to >>this type of manipulation. >> I remember seeing an article about the dangers of ADB. The min-din plugs are so close together, and when you plug the plug in while the machine is on, and the pins get bent and touch together, the ADB chip gets fried. Your machine will go out to lunch. Apple will repair the damage, but they'll repair it by replacing the motherboard instead of replacing the chip, so repairs are quite expensive.
jbr@key.COM (Jeff Rubin) (03/07/90)
Thanks to those who emailed responses to me about playing with ADB devices with power on. Here is a summary of the responses: ------------------------------------------------------ From: dwade@jarthur.Claremont.edu ADB devices are indeed powered on. I've never had a hardware problem as a result of unplugging ADB devices, but I have gotten crashes rarely and generally the Mac just refuses to recognize the device. I am under the impression that a fair amount of information is exchanged at startup between the keyboard and the Mac, so presumably this information is lost when the device is unplugged. I know that if you plug two Macs into one keyboard you're asking for lots of problems, including hardware problems... ------------------------------------------------------ From: rrkasegu@ATHENA.MIT.EDU [Does the triangle power on key use the ADB?] No, it doesn't. Pin 2 of the 4-pin ADB connector is connected to the ground pin of the ADB connector when the triangle button is pressed. The power-on circuitry detects when that pin is grounded (the power on button does the same, I believe), and turns on the power. The power line is not live when the power is off, nor is the ADB circuitry on the main board. ------------------------------------------------------ From: dplatt@coherent.com The main ADB-bus power line is run through a small surface-mount fuse soldered to the motherboard (on the Mac II, at least). If you plug or unplug an ADB connection with the power on, there's some chance that you'll accidentally short the plug's ADB-power pin to the metal shell on the jack... which is grounded. This will dump +5 through the short, and blow the fuse on the motherboard. If your Mac is not under warranty or AppleCare, you can simply tack-solder a small fuse-holder to the ends of the fried chip-fuse, and install a user-replaceable fuse... I've heard from people who have done this. The "power on" key is not tied into the main ADB power, nor does it use the standard ADB data-transfer mechanisms.. It's a simple electronic mechanism, driven by the Mac's battery through a _very_ large resistor. When you press the power-on key, it deliberately grounds the power-on line on the ADB; a sensor in the Mac detects the fact that a very small amount of current is flowing, and triggers the power-supply-activation logic. I don't believe that accidentally grounding this lead will do any harm to the Mac circuitry... it'll just trigger the power-on process. The power-on circuit draws _very_ little current... you can actually force the Mac to boot by simply bridging the switch contacts with a slightly sweaty fingertip! If you were to accidentally short _both_ the ADB power line and the power-on line to ground simultaneously, you might possibly do some damage, since the Mac would power up and then blow the ADB fuse... but I'm not certain that this is physically possible given the design of the mini-DIN plug. You might want to pull the AC plug, just to make triply sure... but this is probably carrying caution to the point of excess. I've NEVER heard a report of anybody frying their ADB if they had powered the Mac down before fiddling cables. ------------------------------------------------------ Again, thanks to all. It would seem this is a case of RTFW. (The W is for warranty) ------------------------------------------------------------------- Jeff Rubin "I thank you from the heart of my bottom" -anon ...!amdahl!key!jbr