Relay-Version: version B 2.10 5/3/83; site utzoo.UUCP Posting-Version: version B 2.10.2 9/18/84; site islenet.UUCP Path: utzoo!linus!philabs!cmcl2!seismo!lll-crg!dual!islenet!bob From: bob@islenet.UUCP (Bob Cunningham) Newsgroups: net.dcom Subject: Re: lightning, PACXs and computers (followup) Message-ID: <1465@islenet.UUCP> Date: Sat, 10-Aug-85 20:14:22 EDT Article-I.D.: islenet.1465 Posted: Sat Aug 10 20:14:22 1985 Date-Received: Sat, 17-Aug-85 06:09:07 EDT References: <1397@islenet.UUCP> <29116@lanl.ARPA>, <1028@ulysses.UUCP> <1831@ecsvax.UUCP> Organization: Hawaii Institute of Geophysics Lines: 79 At last count, over 40% of the zapped terminals we had were repairable only by replacing the 1488 and/or 1489 chips (usually the 1488). An industrial-quality solder remover (heater + vacuum pump) is highly recommended. The percentage seems to be slightly higher (better) for port selector boards (Gandalf & Micom). Needless to say, we've been installing sockets for those chips where practical. On the computer side, all the port/multiplexer (DZ or whatever) boards were just swapped out. Not sure what percentage just had driver chips burned out or not. Subsidiary damage (one tape unit and some memory boards) was limited to just 2 systems, and my opinion is that not all the equipment at those locations was solidly tied to a single ground. Besides the followup articles in this newsgroup, I've received a considerable number of mail messages (all appreciated, though I've not had time to send individual replies), falling into two categories: 1) similar horror stories 2) thoughtful advice on lightning protection Apparently, similar incidents (lightning damage via local data comm lines) are much more common & widespread than I'd have thought. Unless you're in a very unusual location, if you've got comm lines going between buildings, be warned: something similar might just happen to you. While I've received a number of very sensible suggestions on lightning protection, there doesn't seem to be one single solution we could adopt in all cases. Suggestions have ranged from using opto-isolators, diodes (of various sorts, including MOVs), to using telco-type spark gap devices, to fiber optics. Each approach has some good points. However, the thought of having to install any particular suggestion on the 800 or so data comm lines around campus which probably should have protection is a sobering thought. Schemes cheap in material (e.g. diodes) look to be rather labor-intensive (if both terminal and computer/port selector ends both need protection -- which seems optimal). Schemes cheap in time (e.g. fiber optics) look a bit expensive in parts (though the thought of pulling a lot of fiber optic cables to replace twisted-pair lines is also rather sobering). So far, I think our best approach here is to stick to the basics. For starters, going over all of the central grounds. All Computer equipment and auxiliary racks within a room should be securely grounded to a single point with generous-size braided ground straps. The objective is to minimize any possible ground differences between computers and their peripherals (including port selectors). It seems to be a good idea to tie down all incoming terminal grounds (RS232 pin 7) to that same point -- as the lines come in (typically on punch blocks). This should localize damage (typically to the port selectors). It also seems reasonable to dedicate whole computer-side port/multiplexer boards to PACX lines ... no more mixing direct-connect and port selector terminals. Typically, the only terminals I want to leave directly connected will be those in the same building (preferrably the same wing) as the computer site. This should also minimize computer-side damage. Fortunately, port selector boards are MUCH cheaper to repair/replace than computer port/multiplexer boards. Relatively expensive terminals (graphics types, for the most part) should get some special form of isolation at their end from the RS232 lines (preferrably something simple that plugs in between the RS232 line and the terminal). Cheaper terminals (< $1,000) I think are best left as-is for now. All NEW inter-building trunks (multiple data comm lines) that I have any control over will be fiber optic lines (stat muxes at each end, of course). We do have some plans for a couple of real LANs around campus. I do believe that specs for those will now definitely include some form of lightning protection. -- Bob Cunningham {dual|vortex|ihnp4}!islenet!bob Hawaii Institute of Geophysics Computing Facilities Honolulu, Hawaii