Part 3 in the ClassicCmp FAQ Trilogy

From: Marvin <>
Date: Fri Jan 19 23:14:32 2001

ClassicCmp - The Classic Computers Discussion List
Part 3 in the ClassicCmp FAQ Trilogy
Technical FAQ (Frequently Asked Questions) v1.6.2
Last Update: 12/10/97
This FAQ is written with the primary purpose of making readily available
answers to the more common questions appearing on ClassicCmp. It is
Maintained by Bill Whitson <>. The infor-
mation in this document has been gathered from a variety of sources but,
in general, the members of ClassicCmp should be credited for all contain-
ed herein. I have, of course, endeavored to be as accurate as is possible
and often failed ;).

This FAQ is Part 3 of the ClassicCmp FAQ Trilogy. The information presented
deals with regularly asked questions which are technical in nature.

If you have questions, comments, or corrections (always welcome) please
contact me at the address above.

A current copy of this FAQ is available on the web at
http://haliotis.bothell or via anonymous FTP at in the
directory /pub/classiccmp/faqs as cclpart3.faq.
Updates: Nothing new, cosmetic changes.
1. General
1.1 I just picked up a new machine. What should I do?
1.2 What's the best way to clean these dingy tan boxes?

2. Media
2.1 What's a hard sector disk? What's a soft sector disk?
2.2 What's SS/SD, DS/DD, DS/QD, DS/HD, etc.
2.3 Can these formats be interchanged?
2.4 What disk sizes are there?
2.5 How do I take care of old media?

3. Component Failure Issues
3.1 Do EPROM's go bad?
3.2 How about ROM's, other chips?
3.3 How about capacitors?
3.4 Anything else?
3.5 So how do I backup all this stuff like you suggest?

4. Software
4.1 Where can I get a system disk for platform X?
4.2 What's the best way to back up my software?

5. Specific Problems/Solutions
5.1 Is it possible to bypass an RF modulator to achieve composite output?
1.1 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, cold (broken) solder joints, bent pins, etc. It
may be a good idea to remove and re-seat all socketed components and
connectors. If anything burned or overheated it will probably pay to
replace it before powering up the unit. You can avoid a number of
problems just by taking a peek inside.

If you have the tools (and the machine is sufficiently rare) pull and
dump backups of all EPROMs, ROMs, and PALs. If you have really cool
tools (like a logic analyzer) it has been suggested that you use them
to record critical information from those oh-so-hard-to-find custom
chips. Specific information on how to do this is beyond the scope of
a FAQ, but you probably know what you need to if you own the appropriate

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. Running the power supply without a load could result in damage to
it. 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 computer for the first time. If you have a really
rare beast it may be worth powering up some of the key capacitors out of
circuit just to get them warmed up.

Now you can power it up. Assuming it works, take a blank disk,
format it, write some data to it, and read it back before using your
precious software with it, as a bad disk drive could really ruin your
1.2 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
care of most jobs. For removing stickers try mineral oil or Goo-Gone
(available at most hardware stores - in the US at least). If those
don't work, acetone can be good but, if overused, can do more harm.
For removing marker, almost any solvent is good (alcohol, naptha, etc)
but will definitely discolor or dissolve plastic if not carefully
applied. Lava soap is also good for removing marker but can smooth off
textured plastic. For removing sun or tobacco discoloring a product
called Purple Stuff available from auto parts stores (again, in the US
at least) seems to do the job almost effortlessly.

Recommended commercial products:

Purple Stuff from Kragen [for discoloration]
Brasso [ink/marker] (can discolor plastic)
Antistatic Foam Cleaner from Electrolube [for discoloration/markings]
Citra-Solv [for discoloration] (can dissolve plastic if undiluted)
Cameo Copper Cleaner [ink/marker]
Naptha [for stickers/goop/spooge] (very flammable)
3M GP Adhesive Remover [for stickers/goop/spooge]
CRC 226 / CRC 556 [for stickers/goop/spooge]
Fulcron [for discoloration]
Blue Shower / BS II [for stickers/goop/spooge]

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.

Recommended commercial products: Electrolube contact cleaning sprays.
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. If there is reason not to use a dishwasher
(some key labels can come off) it is usually possible to remove each
keycap and clean conventionally.


2.1 What's a hard sectored disk? What's a soft sectored disk?

We'll start with soft-sector since they're simpler to explain. On a
soft-sector floppy disk the information that marks where a sector
begins and ends is written to the disk by the computer (part of the
formatting process). This means that various computers can use
the same floppy disk types because the format of the disk is control-
led by the operating system.

Hard sector disks use a system of perforations in the media to mark
the beginnings and ends of sectors. This means that computers
which used hard sectored disks required the exact disk type they
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. 3.5 inch disks never came hard-sectored and, in fact,
it would not be possible.

2.2 What's SS/SD, DS/DD, DS/QD, DS/HD, etc.

These all refer to the number of useable sides on a disk and it's
density (how "efficiently" the magnetic bits are pushed together).
SS/SD is a Single Sided - Single Density disk, the earliest available
type I believe. The storage afforded by a single density disk was
very small compared to today's standards. Single Sided disks were
popular because they were cheaper than DS and could be easily
modified with a hole punch into double sided disks. SD was followed
by Double Density which, amazingly, doubled the amount of storage
space. Double Density was followed by the extremely short-lived
Quad Density which doubled a DD disk. QD was short lived because
High Density was right on it's heels and nearly doubled disk capacity
again. DS/HD was as sophisticated as 5.25" disks became. 3.5"
disks have progressed as far as DS/EHD double-sided / extra-high

2.3 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 DD, HD (sometimes work, not advisable!)
High Density none

Other substitutions may be made, but due to physical differences in
how the disks are made they are generally unreliable. It can almost
be guaranteed that data written to a proper density disk of poor quality
will last longer than data written to a good quality disk of the wrong
density. In the case of quad density no substitution should be
considered reliable. DD and HD disks both can be forced to work. One
may work better than the other given the peculiarities of various drives.

2.4 What disk sizes are there? Disk Types?


Standard Disks Unique/Proprietary Disks
8" (Floppy) 5" (MiniFloppy)
5.25" (MiniFloppy) 3.25" (MicroFloppy)
3.5" (MicroFloppy) 3" (MicroFloppy)

In addition to odd sizes - there is at least one type of disk which
was physically different. "Twiggy" disks for the Apple Lisa 1 were
regular 5.25" disks with the exception that they had two read/write
windows. One was oriented "north" of the center hole, the other "south".

2.5 How do I take care of old media?

Step one is Back It Up! After that, make sure it's kept in a clean, dry,
temperature-controlled environment (I keep mine in a broken freezer).
With disks it seems important to keep them standing on end rather than
lying flat - the same goes for cassette tapes. I like to exercise disks
and tapes at least once every six months although I have no real
evidence that this has any positive effect. I have modified an old C64
floppy drive to simply spin when a disk is inserted and send large
stacks of disks through it on a regular basis just to make sure they're
not starting to stick up internally.

An exciting and somewhat recent development is that availability of
classic computer emulators that can make disk images of old media
on PC's and Macs. This seems to be a very good way to backup
disks since they will eventually go bad no matter how well we take
care of them.

The official line seems to be that floppy disks have a shelf-life of
approximately 10 years. With proper care many are lasting a lot longer.


3.1 Do EPROM's go bad?

Definitely. They apparently are considered to reliably contain data for
(on the outside edge) 15 years. This amount can be considerably
reduced if, for example, the sticker over the window has dried out and
fallen off. Luckily EPROMs were not used too extensively but they're
out there. An EPROM writer/reader is a relatively cheap investment
and an easy fix. Even if an EPROM has "forgotten" it's data it is still
fine for being "re-educated".

3.2 How about ROMs and other chips?

Things wear out. It's likely that even components which have not been
fried by catastrophic failure will simply start to die someday. ROMs can
be dumped to a file and re-written if they die. Other custom chips which
are all too common in micros will be far more difficult to replace. The
best advice is to stockpile these chips when you can - but someday even
unused chips will probably start to turn up bad. In this case the best
defense is to stockpile information in the hope of being able to modify
an existing component to meet your needs.

3.3 How about capacitors?

This seems to be another large concern, but rather than being an
unreplaceable component a capacitor will take your unreplaceable
components with it when it goes. It's a good idea to check out all the
caps in a system if you haven't fired it up in a while. Caps go bad
with time (even tantalum caps, apparently - although they are more
reliable) and should be replaced if they are suspect. It's unlikely that
it will be impossible to find a replacement capacitor as they are much
more standard electronic components.

3.4 Anything else?

Documentation: If there's anything which is entirely unreplaceable its
the docs for uncommon equipment. Once they're gone, they're gone.
I regularly pick up docs I find for equipment I don't have just because
I may someday. Paper will, of course. go bad over time but it will be
obvious and they will be easily duplicated.

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.

3.5 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." Punch tape units are available and apparently not difficult
to use with a PC (PC - the great multi-purpose classic computer
peripheral). Optical tape readers are recommended.

Recommended products: Tape Writers: Facit 4070, Teletype BRPE.
                       Tape Readers: Trend 700


4.1 Where do I get a system disk for platform X?

Since this is a tough one, let me break it down a little:

Apple II: System disks for the Apple II are available from Apple at Apple III system disks aren't available although
probably will be soon on the ClassicCmp site. Apple Lisa disks aren't
availble and probably will not be due to the extreme measure of copy
protection used on them. Older Mac system software is availble on the
Apple site.

CP/M Systems: Ak! These can be a pain. The best source (although
I've never actually talked to him) seems to be Don Maslin who runs the
Dina-SIG system disk archive. He charges a small fee for the service
- which I imagine is well worth the cost! He can be contacted on the
internet at <>.

Other systems - let me know.

4.2 What's the best way to back up my software?

One of the most promising ways that has come up is to use a PC with
a soundcard as a really expensive cassette recorder for data storage.
Fundamentally there's not much difference between a real recorder and
and a PC equipped with sound. By storing your software in your favorite
PC sound file format you can then back up to CD or tape or whatever PC
medium you like. Most micros came equipped with the ability to store
programs to tape and I would imagine that it would be easy to modify
computers without this capability to use one.

In addition, the rapid rise in the popularity of emulators has given
rise to a number of disk image formats for old machines. In many cases
it is possible to read/write disk images for classic computers with
modern PCs.


5.1 Is it possible to bypass an RF modulator to achieve composite output?

Possibly - depending on what you're working on. In the simplest case it is
possible to simply run off of the inputs to the modulator right to your
monitor. Some setups will apparently require a video amplifier. It has
also been suggested that it may help to turn of the termination switch at
the monitor.
Thanks go out to the following people for much of this information:
(some credited by e-mail handle)

Adam Bergstrom Kai Kaltenbach
Alexios Chouchoulas Keith Whitehead
Captain Napalm Ricardo Romagnoli
Chris Starling J. Maynard Gelinas
Dave Jenner
Douglas Zander
George Lin
Greg Mast
Jay Vaughn
Jeff Hellige
Jim Strickland
Jim Willing
Larry Anderson
Martin Evans
Paul Coad
Roger Merchberger
Ron Mitchell
Sam Ismail
Tony (A.R. Duell)
William Donzelli
Received on Fri Jan 19 2001 - 23:14:32 GMT

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