test-drb October 1999

test-drb@ccmp.vtda.org

216 participants
748 discussions

Running a 220v computer in a 110v environment

by Philip.Belben＠pgen.com

Peter Pachla quoting [I forget whom] > > A fuse will never protect _you_ nor the device. It is only ment > >to protect the house/the installation.... > > This I have to take issue with (though I'm probably quibbling over > semantics?). > > The purpose of the fuse in the PLUG is to protect the power cable between the > plug and the device from carrying an unsafe current in the event of a problem > with that CABLE. > > The device itself should contain a second fuse which is there to protect the > PSU in the event of a failure or overload. > > At least that's what we were taught when I did an electronics course a few > years back. Right. I think there are some misconceptions around here that need clearing up. I will put in a disclaimer that I am not an electronic engineer but an electrical engineer - my field ends roughly where the power cord enters the computer! - but many of the principles carry across between the fields. Misconception 1: A fuse or breaker in the live (hot) wire means that a person touching live metalwork will not get a fatal shock. THIS IS TOTALLY FALSE - which is I think what our previous contributor was getting at. A fuse or breaker is intended to interrupt the circuit when there is an excessive current flowing. Since it can take as little as a milliamp to kill someone, and very few people survive more than 30mA, a fuse is unlikely to help. The fuse - as Tony and Peter have both pointed out - performs what might be called damage limitation on the device. One fault causes excessive current; the fuse prevents the excessive current causing further faults, either upstream or dounstream. Misconception 2: Earthed (grounded) metalwork is safe. It is usually safe, PROVIDED fuses and things are in place, AND THE EQUIPMENT HAS BEEN PROPERLY DESIGNED. Anyone who has designed electronics will have encountered earth path resistance. If there is a large current flowing in the earth path, the potential of nominally grounded points can rise. (In digital circuits this is usually a transient phenomenon, where a switching surge puts glitches on signals that should be constant at ground potential. This has the disadvantage that inductance is also significant...) When designing electrical equipment, it is important to keep the resistance of the earth path low enough that in the event of a short circuit, the potential of (say) the chassis will not rise too high. So how high is too high? The answer depends on the length of time for which the potential will be present - the longer it is there, the more likely it is to kill the person writhing on the floor unable to release their finger muscles... The length of time the high potential is present depends - of course - on the fuse or breaker. Fortunately there is negative feedback - the lower the current, the longer the fuse takes to blow; but the lower will be the potential rise, so the lower will be the current flowing in the person touching it. In this sense the fuse protects you - in the event of a short circuit, it cuts off the current before a high voltage has been present on the "earthed" chassis long enough to kill you. But remember, THE CURRENT FLOWING IN _YOU_ IS DEPENDENT ONLY ON VOLTAGE (and on how you make contact - but not on the circuit to which you're connected) - your resistance is so high (kilohms) that your effect on short circuit currents or fuses is NEGLIGIBLE. (OK, perhaps someone will come up with an exception - but it is best to assume that this always applies. I know of no exceptions on domestic mains...) If you are running electrical equipment and a fuse blows, YOU MUST DISCONNECT IT before you go poking around inside. NEVER rely on the open-circuited fuse to protect you (which may also be what our previous contributor was getting at). If you are running British equipment from a US 120-0-120 supply, and there is a short to ground near the hot end, the fuse will blow in the normal way. This will interrupt most of the current, but will leave the other side of the supply connected through most of the device to ground. An earth leakage trip (ELCB, RCD, GFCI) [1] is required to pick up the remainder of the fault current and disconnect altogether. If there is a short to ground near the neutral end, only the ELCB (and possibly the main breaker or fuse at the consumer unit) will see it. This is the disadvantage of running British (or European) equipment on US 220V mains. The fact that parts of the innards will be live (hot) when a single pole switch is opened or a fuse blows is IRRELEVANT, because YOU SHOULD BE UNPLUGGING BEFORE YOU GO POKING AROUND INSIDE ANYWAY. If you have to run stuff with the cover off, be aware of the dangers, and take precautions to minimise the risk. But this too goes for all equipment anyway. I hope this clears up some misconceptions. Philip. [1] Earth leakage trips: ELCB = Earth Leakage Circuit Breaker (UK) GFCI = Ground Fault Circuit Interrupter (US) These are generally Residual Current Devices (RCD) - detecting the difference between hot and neutral currents. Some older trip switches were not RCDs, but measured ground potential rise instead, but these are not recommended for new designs - or for old ones for that matter! They should still work for any fault that makes a chassis potentially (pun intended) dangerous to touch. This E-mail message is private and confidential and should only be read by those to whom it is addressed. If you are not the intended recipient, you are hereby notified that any dissemination, distribution, copying, reproduction, modification or publication of this communication is strictly prohibited. Please delete the message from your computer and destroy any copies. This message is not intended to be relied upon by any person without subsequent written confirmation of its contents. This company therefore disclaims all responsibility and accepts no liability of any kind which may arise from any person acting, or refraining from acting, upon the contents of the message without having had subsequent written confirmation. If you have received this communication in error, or if any problems occur in transmission please notify us immediately by telephone on +44 (0)2476 425474

25 years, 2 months

Floppy disks again

by pete＠dunnington.u-net.com

On Oct 12, 18:55, Clint Wolff (VAX collector) wrote: > On Tue, 12 Oct 1999 allisonp(a)world.std.com wrote: > > > There are two media for 96tpi, one for DD and lower and is the SAME > > magnetic material as 48tpi. THere is also the 1.2mb media and this is > > VERY DIFFERENT and incompatable with any other drive or density. > > > > So if we ignore 1.2mb media and the oddbal spindle speeds and data rates > > that go with it we come down to one media (softs sector) and 6 different > > drives over the years. They are: > > > > 48tpi single sided (sa400) > > 48tpi double sided (sa450) > > 96tpi single sided (teac Fd55E or DEC RX50) > > 96tpi double sided (teac FD55F) > > 100tpi single and double sided models (micropolis I think) > > > > Ok, I wasn't aware of any 96tpi drives except the HD ones... Were > they ever used in the PC marketplace, or was it mostly a DEC thing? > After re-reading my uVAX manual about the RX50, I agree it is a > 96tpi single sided drive, though the manual says: "Use only formatted > RX50 diskettes, available from DIGITAL or its licensed distributors" They were used practically everywhere *except* in IBM/Intel/Microsoft PCs. They're certainly not unique to DEC. IBM/Microsoft seemed to want to standardise (not unreasonable!) and picked a particular format/size (with minor variations). The reason the manual says "Use only formatted RX50 diskettes" is that formatting the 10 sectors/track on an RX50 is rather critical, and most DEC machines to which those drives were connected, weren't supplied with formatting software. Rainbows were, though (I think), and I regularly format RX50s on other machines. > So there are four drives using the same media: > SSDD 180K,48tpi,40tracks/side > DSDD 360K,48tpi,40tracks/side > RX50 360K,96tpi,80tracks/side > ???? 720K,96tpi,80tracks/side - What was (is) this called? DSQD? The number of tracks has nothing whatsoever to do with the density! RX50 is SSDD, it just happens to have 10 sectors of 512 bytes per track, and 80 tracks. Your "??? 720K" is DSDD. Yes, some people did call this QD, but it isn't a different density at all -- the misnomer comes from people who don't understand what the words mean. Your numbers for 180K, 360K, etc, assume a particular number and size of sectors, which need not be the case (ie you can use the same drive and media to make a disk of different capacity). Also, there's nothing about (most) drives that makes them inherently single density or double density; that is just a question of how you interleave clock and data pulses, and how fast you send them down the Write Data line to the drive. > And the HD drive: > DSHD 1.2M,96tpi,80tracks/side - can read older media, but writing > is unreliable (head isn't wide > enough to erase the whole old track) Not so, the head is exactly the right width and layout for any 96 tpi DD (or SD, come to that) media. You just have to make sure it's set to the correct write current. -- Pete Peter Turnbull Dept. of Computer Science University of York

25 years, 2 months

Yet another "free stuff" bonanza

by af-list＠lafleur.wfi-inc.com

Well, in the spirit of all the "free stuff" sharing going around, I dug out a few more things to share... 1) Apple Mac+ keyboard, no cable, dirty 2) An HP 9123 drive for the TouchScreen II (150), beaten up, no PS 3) IBM Thinkpad 560 w/cracked LCD and missing a mouse button 4) Kaypro 4 "Parts" (2 kbds, whatever you want me to remove) from 2 already-somewhat-stripped machines Preference is always given to anyone who can pick up (SoCal), sorry. If someone was really interested in creating a big love/share fest, I'm looking for some 4meg memory modules for my mac IIfx... Cheers, Aaron

25 years, 2 months

HP 9123 disk drive was Re: Yet another "free stuff" bonanza

by rigdonj＠intellistar.net

At 09:27 AM 10/13/99 -0700, Aaron wrote: >Well, in the spirit of all the "free stuff" sharing going around, I dug >out a few more things to share... > >1) Apple Mac+ keyboard, no cable, dirty >2) An HP 9123 drive for the TouchScreen II (150), beaten up, no PS The 9123 doesn't have a power supply. It gets it's power from the TouchScreen II through the five pin DIN connector. Except for the power supply, the 9123 is the same as the 9122 (double sided 3.5" Sony floppy drives). You can connect it to a +5 and 12 VDC power supply and use it like a 9122. Joe

25 years, 2 months

paper tape repair

by jlwest＠tseinc.com

Greetings! I have a paper tape that got messed up when I was trying to rewind it in a rather non-conventional way <grin>. I have several copies of the tape so it's no big deal, but I'd like to fix the messed up one. I seem to remember years ago seeing a paper tape repair kit that had clear tape with all holes punched in it. This was to be taped over the problem area. Is this type of thing still available anywhere, or are there other methods of repair people have found here? Thanks in advance! Jay West

25 years, 2 months

Old 8086 Amstrad

by musicman38＠mindspring.com

WOW! Great Timing on the infor for the Amstrad Website.. I can't believe you guys are on the subject of Amstrad PC6400.. I just purchased one at the local Thrift store yesterday for $4.04 and when I got to the checkout line the lady told me it was half price day so for only $2.02 I got this really cool Portable XT dual 720KB floppies, and a nice LCD screen.. Very impressive machine for 1987.. And it appears to run on standard D batteries for portable use.. Looking forward to learning all about it.. Phil... -----Original Message----- From: Olminkhof <jolminkh(a)nsw.bigpond.net.au> To: Discussion re-collecting of classic computers <classiccmp(a)u.washington.edu> Date: Tuesday, October 12, 1999 04:42 AM Subject: Re: Old 8086 Amstrad >I don't know, but here's a link to an Amstrad site: > >http://web.ukonline.co.uk/cliff.lawson/product.htm > > >-----Original Message----- >From: Rodrigo Ventura <yoda(a)isr.ist.utl.pt> >To: Discussion re-collecting of classic computers ><classiccmp(a)u.washington.edu> >Date: Tuesday, 12 October 1999 0:19 >Subject: Old 8086 Amstrad > > >> >> Hi. Anyone knows how to enter the BIOS setup in such a PC? >>Does it even have a BIOS setup utility? >> >> Thanks, >> > >

25 years, 2 months

collectors vs. enthusiasts

by daniel＠internet.look.ca

-----Original Message----- From: Eric Smith <eric(a)brouhaha.com> To: Discussion re-collecting of classic computers <classiccmp(a)u.washington.edu> Date: Wednesday, October 13, 1999 12:29 PM Subject: collectors vs. enthusiasts >> It's crazy. I can't believe what they are paying on EBay for less than >> *incomplete* systems. I could see $1400 with drives, running, tested, >> manuals, etc... but a shell?????? > ><rant> >That's because eBay is where "collectors" hang out. Not people like us, >for whom collector is an insufficient/inaccurate term. Well, if you are looking for a good home for one of stright 8s and for a decent $ then please e-mail me! I won't hang the core memory on the wall and I will get it running! I agree with you on the "collector" term. That PDP 8 was bought for $1300 because it was a nice looking desktop unit. Rack mount minis don't even get bids on EBay! I use EBay to try and buy parts (never heard of any of lists/groups like this one a month ago.). I lost the H214 core memory module I needed from EBay from a sniper bidder wanting to frame it (I think). john > >It's like the difference between coin or stamp collectors and classic >car enthusiasts. A coin or stamp collector gets the coin or stamp he's >been drooling over, puts it in a book or in a display on his wall, >checks it off a list, and he's done. Since coins and stamps don't "do" >anything, that's fine. > >But a classic car enthusiast maintains classic cars in working order (or >at least attempts to do so), and drives them now and then. They're not >just a checklist item. > >A seemingly large percentage of the computer "collectors" on eBay are >just people who see collecting computers exactly like collecting coins. >They don't give a shit whether the thing works, as long as it looks cool >and will impress their friends. Hell, if they got a PDP-8 that did >work, they wouldn't know what to do with it aside from destroying the >core planes to make wall hangings. > >That's why I personally will try never to sell any truly rare items on >eBay. I'd rather make sure that they go to a good home, rather than be >obligated to sell to one of these collector" assholes, just because he >had deep pockets. ></rant> > >Eric >

25 years, 2 months

Where and Where to get an IBM 1130

by cmcmanis＠mcmanis.com

At , Randy M.Kaplan wrote: >1. I have noticed in reading the list that individuals will come upon >various machines in various places that are being retired. I also recently >purchased a Sun IPC from ebay. When I went to pick it up, the fellow had a >yard full of stuff he had apparently scarfed up from various companies. How >does one find out about these sources? Who do you contact? Well a couple of things, if you start collecting old computers many sources will find _you_. Unfortunately many of those sources will want you to take 75 80386SX computers off their hands not IBM 1130s. Look up scrap metal recycling in your yellow pages. These guys are sort of the "sharks" of computer collecting, they devour things indiscriminately but you can be a "trigger fish" and teach them the value of some machines. A good relationship with a top tier scrapper is a really good thing to have. The scrappers watch the new paper for liquidation bids. Places that are scrapping out entire buildings and such. Older and larger computers are sometimes found in these liquidations because the buildings are abandoned and the "big iron" in the machine room is just left there. (I "found" 1/2 of a 370 that way once in a building that was for lease.) >2. I was wondering if anyone had any notion of where I might look for an IBM >1130 or is this a totally ridiculous pursuit. When I started out, this was >the first machine I wrote Fortran programs for. The 1130 is not an easy machine to find. You will have several sources (ranked from most likely to least likely): 1) Another collector who can't afford the space any more and wants to keep the machine in the hands of a caretaker. 2) Some place that had to keep software for it running and kept one around as a "gold standard." 3) A scrapper who hasn't had the heart to crush it yet. 4) IBM (who might have one in a warehouse somewhere for some reason) Its certainly a worthwhile pursuit. --Chuck

25 years, 2 months

Tape drive help and/or part needed (Attention DEC-heads!)

by DSEAGRAV＠toad.xkl.com

I either need to find someone who knows what they're doing with a TU77, or someone who has and can get rid of a TM03 formatter for a TU77 with the special 18-bit card. Chris Zach (cz(a)alembic.crystel.com) has the MIT-AI KS10, and wants to run ITS on it, but his tape drive (A TU77) is screwed up. It generates a FORMATTER ERROR in the Status register whenever it's on. He has booted from drives on the same Massbus so that's OK. Having a real '10 with ITS on the 'net again would be a really good thing. Does anyone think they can help this guy? -------

25 years, 2 months

IBM PC era software

by lemay＠cs.umn.edu

I found some 5.25" floppy disks, apparently from the era of the IBM PC. This stuff could be yours... IBM Diagnostics (version 2.05; IBM Personal Computers) 1983 Lotus 1.2.3 version 2.10 1986 PSpice - electrical Circuit Simulator. Classroom version. Demo versions of pro/bis and pro/sci version 1.0 Borland turbo pascal 8087. version 2.0 1983 Borland Turbo Graphix Toolbox. version 1.05A 1984 Ability Demo Disk 1 & 2 T3 (thats T cubed) Scientific Word Processing System. Beta Version 2.11 Absolutely no documentation for any of this stuff. -Lawrence LeMay lemay(a)cs.umn.edu

25 years, 2 months

← Newer
1
...
46
47
48
49
50
51
52
...
75
Older →

Jump to page:

2024

2023

2022

2021

2020

2019

2018

2017

2016

2015

2014

2013

2012

2011

2010

2009

2008

2007

2006

2005

2004

2003

2002

2001

2000

1999

1998

1997

test-drb October 1999