FAQ Part 3

============================================================================= 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 <bill(a)booster.u.washington.edu>du>. 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 washington.edu/classiccmp or via anonymous FTP at 140.142.225.188 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 tools. 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 day. 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 density. 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? Physically? Standard Disks Unique/Proprietary Disks --------------------------------------------------------- 8" (Floppy) 5" (MiniFloppy) 5.25" (MiniFloppy) 3.25" (MicroFloppy) 3.5" (MicroFloppy) 3" (MicroFloppy) 2.5" 2" 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).