FAQ updates/changes

From: Bill Whitson <bill_at_booster.bothell.washington.edu>
Date: Wed May 21 18:11:07 1997

Hi all.

First - let me just say that I'm the ideal tester of my own FAQ as I'm
the one asking most of the "dumb" questions ;)

> > 2.8 Can I type obscenities about Microsoft in ALL CAPS!?!
> IMHO _no_ advocacy-type posts belong here - not just anti-MS ones. There
> are certain features of certain computers (yes, even classic ones) that I
> don't like (as a hardware designer, for example, I don't regard certain
> parts of the Apple ][ as being particularly elegant). But I don't indend
> to try to start flame wars here. I'll contribute to threads I am
> interested in, and ignore the rest. It appears that, fortunately, all
> other posters operate the same way.

Well, I wasn't singling out MS for exemption - I just thought it was an
entertaining heading ;). The example applies to everything. IMO, it's
fine to post an opinion that some product was poorly designed or
implemented and spawn a discussion about that. It's these design flubs
and quirks of the industry that have moved the evolution of computers.
It's another thing entirely to say Company X sucks and employs only
incompetent morons. No useful discussion can be extracted from such a
post. I will generalize the section.

You'll have to excuse my paranoia - but I've reached a point where so
many groups/lists I used to read have degenerated that I really try to
head things off here. I'm the only hair-trigger asshole allowed ;)

> > 5.4 I just picked up a new machine. What should I do?
> Also look for dry joints (broken solder connections), IC's with pins bent
> under, etc. If you like, reseat all internal connectors. You may cure a
> number of faults by doing that.
> If anything looks overheated or burnt out, take great care. Some damage
> may already have been done, but you want to ensure no further problems
> occur.

Good advice - I'll add it.

> > If you have the tools (and the machine is sufficiently rare) pull and
> > dump backups of all EPROMs, ROMs, and PALs.
> Also, if you have the knowledge, equipment (a _good_ logic analyser, which
> is not the sort of thing most hobbyists have) and time, it may be worth
> grabbing waveforms arround irreplaceable custom chips when you first power
> up the machine This information may be very useful if you even need to
> recreate them. On the other hand, knowing what to record, and what to
> relate it to, is often non-obvious.

I'll add this. I can't speak for other members of the list but I
suspect many may be in the same boat as I. I only started accumulating
equipment about 5 years ago and I've learned everything I know about
electronics in the process of attempting to fix the various things I've
picked up. Even if someone gave me a logic analyzer I couldn't do a
damn thing with it. To be honest - I don't really have a solid concept
of what a logic analyzer does ;). My main tool is a DMM and I've barely
come to understand what I can do with it ;). I've got an oscilloscope
but that's only so I can align floppy drives - that's the only trick
I know how to do with it. I can dump a copy of an EPROM but I'd be
hard-pressed to copy anything else. The recommendations in the FAQ have
already surpassed my ability to use them.

I've gotten into collecting old computers because I enjoyed using them
as a kid - my problem now is that some of what I own may be slipping
away faster than I can learn how to fix it!

> > Disconnect the power supply from the rest of the computer and
> > start it up on a "dummy load". A six volt headlight bulb has been
> The point of the dummy load is to protect the PSU. Some switch-mode
> PSUs (that's the type used on a large number of computers, including
> almost all PCs) will fail if turned on with no load, even if working
> properly. This would probably be mentioned in the tech manual, but you
> probably don't have that.
> Related to the last comment: A remarkably large number of machines used
> 'standard' PSU modules, which were not built by the company that built the
> rest of the machine. PSU details/schematics may well not be in the service
> manual, which is a right pain, since PSU problems are probably the most
> common fault of all. Sometimes the company that built the PSU will supply
> their own service manual, but often you have to work blind.

More good info which I will add.

> > 6.1 What's the best way to clean these dingy tan boxes?
> I've found a product called 'Antistatic foam cleaner' produced by
> Electrolube to be _excellent_ at cleaning computer cases.
> In the UK, you can get that from Maplin. It's not cheap, but it works.
> Again, Electrolube produce a couple of contact-cleaning sprays. One is 99%
> propan-2-ol, and is safe on just about anything. The other one _may_
> attack some plastics (although not circuit boards AFAIK), but deals with
> dirtier parts. Again, available from Maplin, expensive, but useful.
> >
> > Keyboards: I find a cycle through the dishwasher does a really nice
> > job on keyboards. Just be sure they're completely dry before you
> > put any power to them.
> I normally pull the keycaps (make a chart showing how to put them back -
> squared graph paper is handy here), and clean them like I clean the cases.
> > 7.1 What's a hard sectored disk? What's a soft sectored disk?
> There couldn't be a hard-sectored 3.5" disk. Unlike the larger sizes, the
> index sensor in a 3.5" drive doesn't detect a hole in the disk - it
> detects a magnet or hole in the rotor of the spindle motor (It's shown in
> the Teac FD235 service manual, for example). The 3.5" disk is aligned on
> the spindle when the disk is inserted, so that the position of the index
> pulse relates to the correct position on the disk.
> Since the sensor only produces one pulse per disk revolution, it's
> impossible (no matter what you do to the disk) to have a hard-sectored
> 3.5" floppy in the traditional sense.

Great - I'll update that!

> > 7.3 Can these formats be interchanged?
> >
> > Well, that may depend on what computer you are using, but in general
> > the following substitutions may be made:
> >
> > Desired Format Substitute
> > ---------------------------------------------------
> > Single Density Double Density
> > Double Density none reliably
> > Quad Density High Density
> No! The media _is_ different magnetically. Quad density (80trk 5.25" disks
> with about 700-800K capacity) drives will not reliably work with high
> density (1.2Mbyte) media. Please don't do it.

Hrm. I have done this rather successfully in the past. I know the media
is different (ferrite vs. cobalt, I think) but I have formatted and used
HD disks in a QD drive without problems. At the same time I have found
problems using a HD in a DD drive. I'll remove this piece to prevent
problems but given the relative rarity of QD disks I'm interested to
know if anyone else has found this to work.

> [... Irreplaceable components]
> > Hard Disks: ST-251s, ST-502s, MFM, RLL... old hard disks are going
> > to go bad. Then they'll be gone. Theoretically, I suppose it's possible
> > to crack a hard drive and replace a dead bearing, realign, relaminate,
> > etc... but I've never heard of anyone doing these things in their base-
> > ment. Perhaps in another 5 or 10 years many of us will be experts at this.
> >
> No, but some minicomputer enthusiasts do repair demountable drives, like
> RK05's at home... Doing a head swap is fun (for suitable values of 'fun').
> > 8.5 So, how do I back up all this stuff like you suggest?
> >
> Writing : A good, fast paper tape punch. I recomend a Facit 4070 (easy to
> maintain, runs for ever, trivial to link to a PC parallel port)), or a
> Teletype BRPE (a little faster, more work to interface and keep going).
> Reading : A pair of eyes :-). Oh, you want to do it automatically? In that
> case, a good _optical_ tape reader. If you can find one (and they
> sometimes turn up in the UK), get a Trend 700. They are _very_ kind to the
> tapes, unlike some lesser readers that can mangle sproket holes (or worse
> data holes) in the event of a tape jam.
> Of course, those are classic peripherals in their own right, and could
> probably be discussed here (we can talk about peripherals, and not just
> CPUs, right?)

You bet. If it relates to classic computers...

So, assuming people other than me with little background in electronics
are collecting computers and finding they need to teach themselves how
to fix them what would you experts out there recommend? Books?
Experimentation? (Whaddaya mean discharge the CRT? ZAP!) Give up and
buy stuff that works? I don't spend a whole lot of time working on
this stuff and when I do I get a sneaking suspicion that I'm not as
smart as I think I am.


      Bill Whitson - Classic Computers ListOp
bill_at_booster.u.washinton.edu or bcw_at_u.washington.edu
Received on Wed May 21 1997 - 18:11:07 BST

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