harrow@exodus.DEC (Jeff Harrow, NCSE LKG1-3/F16 DTN=226-7445) (01/18/86)
This afternoon I was plugging my Modem port into an extension RS-232 (DB25) cable and, as I fiddled with the plugs to get them to mate, noticed out of the corner of my eye that the Mac's screen dimmed toward black at one point. I quickly realized that this was due to a misallignment of the DB25 connectors, where, as I attempted to mate them, the grounded portion of the female plug apparently shorted the +5 provided on the modem cable!!!!! I was lucky in that (apparently, and hopefully!) no damage was done, but ***BE CAREFUL***, as I recall reading that the current is NOT limited on these pins. Jeff
jww@sdcsvax.UUCP (Joel West) (01/18/86)
In article <527@decwrl.DEC.COM>, harrow@exodus.DEC (Jeff Harrow) writes: > This afternoon I was plugging my Modem port into an extension RS-232 (DB25) > cable and, as I fiddled with the plugs to get them to mate, noticed out of > the corner of my eye that the Mac's screen dimmed toward black at one > point. I quickly realized that this was due to a misallignment of the DB25 > connectors, where, as I attempted to mate them, the grounded portion of the > female plug apparently shorted the +5 provided on the modem cable!!!!!S Rumor has it, this is why, when the smaller connectors (with 1 less pin) were chosen for the Mac+, they dropped the +5V pin (Pin 2 on the DB9) from the connector. Unfortunately, some peripherals expect this (possibly as a power-on indicator). I know the Corvus net won't work. Joel West CACI, Inc. - Federal (c/o UC San Diego) {ucbvax,decvax,ihnp4}!sdcsvax!jww jww@SDCSVAX.ARPA
jimb@amdcad.UUCP (Jim Budler) (01/19/86)
In article <527@decwrl.DEC.COM> harrow@exodus.DEC (Jeff Harrow, NCSE LKG1-3/F16 DTN=226-7445) writes: >connectors, where, as I attempted to mate them, the grounded portion of the >female plug apparently shorted the +5 provided on the modem cable!!!!! > >I was lucky in that (apparently, and hopefully!) no damage was done, but >***BE CAREFUL***, as I recall reading that the current is NOT limited on >these pins. Perhaps this is one of the reasons that, as I understand, the new MacPlus does not have the 5 volts on the ports anymore. Another is that third party vendors were using that 5 volts to power their products. -- Jim Budler Advanced Micro Devices, Inc. (408) 749-5806 Usenet: {ucbvax,decwrl,ihnp4,allegra,intelca}!amdcad!jimb Compuserve: 72415,1200
bart@reed.UUCP (Bart Massey) (01/20/86)
> This afternoon I was plugging my Modem port into an extension RS-232 (DB25) > cable and, as I fiddled with the plugs to get them to mate, noticed out of > the corner of my eye that the Mac's screen dimmed toward black at one > point. I quickly realized that this was due to a misallignment of the DB25 > connectors, where, as I attempted to mate them, the grounded portion of the > female plug apparently shorted the +5 provided on the modem cable!!!!! > > I was lucky in that (apparently, and hopefully!) no damage was done, but > ***BE CAREFUL***, as I recall reading that the current is NOT limited on > these pins. > > Jeff Better yet, I once thought that it was ok to build mac-mac cables with the +5 pins connected together. Big mistake, as we found out when we realized that if one mac was on and the other off, the on one powers the logic board of the off one through that 5-volt pin!!!! You have been warned... Bart Massey ..tektronix!reed!bart "Wait, why is that Mac drive whirring with the power turned off?" "Must be the serial cable."