rashid@magnus.ircc.ohio-state.edu (Robert G Rashid) (03/04/91)
I have a mac+ with what appears to be a slightly low voltage power supply. I had previously complained in c.s.m.h. about bombs when inserting disks, which lead to a recommendation to purchase Larry Pina's excellent book on mac upgrade and repairs. With this book and my limited skills, I have been monitoring the 5 volt supply from the disk drive port. What I see is a voltage that starts at about 4.98 and, over the period of an hour, rises to 5.01 or 5.02. This rise is consistent, and usually, when the voltage is at 5.01(2), the voltage drop when inserting a disk does not cause a system crash or reset. My question(s): - Is this voltage change normal? - Is it ok to set the initial voltage (when cold) to 5.0 volts? (if set to 5.0 volts initially, will the 'warm' voltage of 5.3(4) be too much?) Many thanks for any thoughts. -- | Bob Rashid | Rashid.1@osu.edu | | College of Dentistry | 305 W. 12th Ave. | | The Ohio State University | Columbus, OH 43210 |
davisson@milton.u.washington.edu (Gordon Davisson) (03/09/91)
In article <1991Mar4.022126.29609@magnus.ircc.ohio-state.edu> rashid@magnus.ircc.ohio-state.edu (Robert G Rashid) writes: >I have a mac+ with what appears to be a slightly low voltage power >supply. I had previously complained in c.s.m.h. about bombs when >inserting disks, which lead to a recommendation to purchase Larry Pina's >excellent book on mac upgrade and repairs. With this book and my >limited skills, I have been monitoring the 5 volt supply from the disk >drive port. What I see is a voltage that starts at about 4.98 and, over >the period of an hour, rises to 5.01 or 5.02. This rise is consistent, >and usually, when the voltage is at 5.01(2), the voltage drop when >inserting a disk does not cause a system crash or reset. > >My question(s): > - Is this voltage change normal? > - Is it ok to set the initial voltage (when cold) to 5.0 volts? (if set >to 5.0 volts initially, will the 'warm' voltage of 5.3(4) be too much?) A bit of variation is normal, and the amount you're seeing is (in my experience) not enough to worry about. I've never seen a Mac 128/512/ Plus that'd run at 5.00 but not at 4.80. (Though there's quite a bit of variation -- some'll run almost perfectly at 4.5, others'll fail almost completely at 4.75.) If I remember your original posting right, you have a snap-on memory upgrade, and are getting 0300FF errors, right? The 03 means a RAM check failed, and the 00FF means bits 0-7 are failing and 8-15 are ok (the Plus has a 16-bit bus) (if it's FF00, bits 0-7 are ok and 8-15 are failing). I'd suspect that the upgrade's connection with the mother- board is flaky at some point (and presumably the jar of a disk insert is triggering the problem). Loosing half the bus like that tends to suggest that one of the bus drivers (the 74LS244's at one end of the CPU) isn't getting everything it needs. Try pulling the motherboard out and giving the upgrade a wiggle -- don't pull it off, just move it up and down a hair to wipe the contact surfaces. This is *not* a permanent fix; the only permanent fix is to not have a snap-on upgrade. :-( >Many thanks for any thoughts. >-- > | Bob Rashid | Rashid.1@osu.edu | > | College of Dentistry | 305 W. 12th Ave. | > | The Ohio State University | Columbus, OH 43210 | No problem; hope this helps. -- Gordon Davisson Westwind Computing (206) 632-8141 4518 University Way NE, Suite 313, Seattle WA 98105