01-Sep-1989 1104) (09/01/89)
Hi World....
I just recently installed yet another HD to my MAC (My third) and now I have
a problem.
Unless the new disk is turned on, my system will just flash the 'waiting for
a disk to boot' question mark.
Now, my setup is kind of unstandard and looks like this:
Mac II, 5 meg
SCSI ID=2 SCSI ID=0
+-----------+ +------------------------+
| | | |
--------------+ +----+HD#1-------+------+Apple 80 Internal |
Mac Internal| | |Not | |(Apple terminates this) |
SCSI +===+ |Terminated | +------------------------+
| +-----------+
External|
SCSI +===+ +----------+ +------------+ +-----------+
| | | | | | | | +-----------+
--------------+ +---+HD#2 +---+Tape Backup +--+Apple CDROM+-+Termination+
|Not | | Not | | Not | | Pack |
|Terminated| | Terminated | | Terminated| +-----------+
+----------+ +------------+ +-----------+
SCSI ID=5 SCSI ID=1 SCSI ID=3
termination Pack is the little thing you plug into the last device on your bus
in the devices second scsi connector.
The Apple CDROM unit is always on, and up to now, I can leave the Tape
backup unit and the disk above marked HD#1 off with no problem.
But for some reason HD#2 must be ON for the system to work....
I boot off of the Apple 80meg internal.
Any ideas?
Phil Huntedbu@pogo.WV.TEK.COM (Ed Burress) (09/02/89)
> Unless the new disk is turned on, my system will just flash the 'waiting for > a disk to boot' question mark. > But for some reason HD#2 must be ON for the system to work.... > Any ideas? > > Phil Hunt Your problem may be that the SCSI termination power on pin 25 of the external SCSI connector is not being provided. The power is provided through a 1 Amp fuse which may have opened due to "hot plugging", excessive loading, or accidental shorting of this supply to ground (which they provide at pin 24). I've looked at this problem here in my own group, as well as several places in our company, and found this the the root of the cause for the problem you have described in every case. Since you have so many devices hooked to the SCSI bus, it could be that the supply is being loaded down sufficiently to cause the same symptoms, but I doubt this is the case. If your Mac is still under warranty, take it in to have the SCSI termination power checked. If your Mac has no warranty, and you feel comfortable with the idea of testing your Mac yourself, then heres a little help: To find out if your SCSI fuse has been blown, probe pin 24, and 25 of the external connector with a volt meter, if it shows 5 volts DC, then the fuse is not the problem. WARNING: BE ESPECIALLY CAREFUL NOT TO SHORT THE PINS TOGETHER WHILE MEASURING, OR YOU *WILL* SNUFF THE FUSE. After inspection, if the fuse has been found to be bad, there are three things you may do: 1. Pay an authorized apple service center $429 to have the board replaced ( no they don't replace the fuse ) 2. Throw the Mac away. 3. Replace the fuse yourself ( only if you can use a soldering iron, yes they solder them in so that they can get you to do #1 or #2 above.) If you opt for #3 as I did, the fuse is located near the rear of the macintosh , under the disk shelf, and hidden under a ribbon cable, it's labeled F1. I hope this helps.....but if you screw-up, remember, you're on your own. -------------------------------------------------------------- U.S. Mail: edbu@pogo Ed Burress 63-356 Phone (503)-685-3200 Tektronix, Inc. PO box 500 Beaverton, Oregon, 97077 -------------------------------------------------------------- "A wise monkey never monkeys with another monkey's monkey." --------------------------------------------------------------