Regular Posting: FAQ

From: A.R. Duell <>
Date: Wed May 21 22:28:36 1997

> ============================================================================
> ClassicCmp - The Classic Computers Discussion List
> FAQ (Frequently Asked Questions) v1.3
> Last Update: 5/2/97
> ----------------------------------------------------------------------------

I hope it's OK to comment on the FAQ here - there are a few things that
IMHO should be expanded...

It's probably better to discuss them on the list, though, rather than use
private e-mail.

> 2.8 Can I type obscenities about Microsoft in ALL CAPS!?!
> Check your anti-MS baggage at the door, please. We all have our opinions
> about MS and their products but it's best to stick to discussing them in
> reference to _Classic_ computers. MS bashing is not only off-topic but
> potentially insulting to those members of the list who work for them.

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.

> 5.4 I just picked up a new machine. What should I do?
> Don't power it up yet! All of the following should probably be done
> before that power switch gets flipped.
> Open the case - clean and visually inspect components. You're
> looking for traces of smoke, water, corrosion, loose screws, blown
> caps and resistors, etc. You can avoid a number of problems just
> by taking a peek inside.

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

> 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.

> 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
> recommended as a convenient load. These should be available
> from any decent Volkswagen shop. Hopefully this will prevent frying
> the rest of the machine with a flaky power supply. You may want to
> check the voltage output before you do this as it could be no where
> near the 5V average in micros. Even if you don't want to connect
> a load it's still probably a good idea to power it up separately from

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.

> [][][][][][][][][][]
> 6.1 What's the best way to clean these dingy tan boxes?
> Cases: It seems best to start gently with such old equipment. Try
> soaking in a little water and dish soap and then scrubbing. This takes

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.

> Connectors: For edge connectors a plain pink eraser seems good
> for removing corrosion. Apparently other colors of eraser indicate a
> different texture - which may be damaging. Make sure to wipe the
> connectors with a clean cloth after erasing on them. There are a large
> number chemicals on the market that "magically" remove corrosion from
> components but as I don't know how safe they are, I'm not anxious to
> promote any of them. For pin style connectors a toothbrush and some
> softscrub or other mildly abrasive cleaner do wonders.

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?

> specified rather than a generic soft-sector floppy. A number of
> differently sectored disks were available - at least 10, 13, and 16
> sector formats. 8 inch and 5.25 inch disks commonly used hard
> sectoring. To my knowledge it was never used with 3.5 inch disks.

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.

> 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.

[... 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?
> This answer will undoubtedly get longer as I learn more. The best ways
> seem to be to dump the particular ROM (or whatever) using the approp-
> riate equipment to a floppy disk (which most of this equipment allows).
> >From there you can transfer the data to either a CD-ROM - convenient
> but not long term reliable storage or to mylar tape which may be
> inconvenient - but the official word on how long it lasts is "Damn near
> forever." I do not know what equipment is necessary to read and write
> punch tape but I'm sure someone will bring it up.

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?)

The gates in my computer are AND,OR and NOT, not Bill
Received on Wed May 21 1997 - 22:28:36 BST

This archive was generated by hypermail 2.3.0 : Fri Oct 10 2014 - 23:30:33 BST