info-mac@uw-beaver (info-mac) (11/27/84)
From: mknox@ut-ngp.ARPA (mknox) One of those little problems for the ulcer prone: I recently added an external 3.5 drive for my MAC. It worked for a few days just sitting by the MAC. Then I got industrious and built this nice little set of shelves, with a 'perfect' place for the drive. Just to the left of the MAC, and up about nine inches above the table where the MAC sat. I also rotated the MAC to the right slightly, so that it pointed more toward where I sit. My external disk drive stopped working. Hummm, whirrr, no read/write. Just 'bad disk' messages. I moved the drive for a better look, AND IT STARTED WORKING!!! 'Ah Ha!' said I, 'It is a bad cable.' But the cabled checked good. Finally I got an idea. Out with an old stainless steel cookie sheet. Place it between the MAC and drive. Perfect operation. No cookie sheet (and the drive back on its shelf), can't read a thing. Solution: rather than design a Faraday cage for the drive, I added another little shelf about 4 inches lower, and about 4 inches further away from the MAC. No problems. Cause? Probably RFI from the flyback xformer in the MAC (second harmonic is near the bit-rate on the drive). It only causes failure in close proximity, within a fairly narrow range of angle and position. But the failure is VERY repeatable. If you are having trouble, try moving your drive a little (point it away from the MAC seems safe for a test). I haven't seen a design like this since the external drive on the old TRS-80 Model-I (same problem).
info-mac@uw-beaver (01/11/85)
From: Rob C. Chang <CHANG@SU-SCORE.ARPA> Does anyone know what signals are sent to/from the external disk drive for the Macintosh? Thanks, Rob Chang CHANG@SCORE -------