FAQ updates/changes

From: A.R. Duell <ard12_at_eng.cam.ac.uk>
Date: Thu May 22 11:43:58 1997

[Advocacy, etc]
> 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

Agreed, keep the heading - it is entertaining. I just think you should
possibly expand the text under it.

> fine to post an opinion that some product was poorly designed or
> implemented and spawn a discussion about that. It's these design flubs

A reasoned discussion of poor designs is (IMHO) fine. Notice the
'reasoned'. It's especially useful when the design fault can cause further
damage - a trivial example is that on some PERQ hard disk interface boards
(the so-called 5.25" DIB), a loss of the +5V line can corrupt entire
tracks on the hard disk. This is a design error (they used totem-pole
drivers, not open collector ones), and it can cause the loss of data.

> 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.

Agreed 100%. Lets keep that off this list. It benefits nobody.

> 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

I suspect there are all levels of knowledge on this list, which is a good
thing. Tips should therefore be aimed at all levels of knowledge, from
those who are starting out (like explicit instructions on how to test a
linear PSU) up to those who'd quite happily redesign the machine given
half a chance :-)

> 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

I learnt a lot about processor design by working on old minicomputers and
workstations. It's one thing to read about a fetch/execute cycle, it's
quite another to trace it in the microcode, see what gates are enabled and
when and watch the data moving about on a 'scope or analyser screen.

However, this won't teach you basic electronics. That's something best
learnt by experimenting with _replaceable_ components - not strange chips
from a classic computer. I'll recomend 'The Art of Electronics' by
Horrowitz and Hill as a good book to learn from, but feel free to recomend

> 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

It's basically a special-purpose storage 'scope that works with digital
signals only, and displays the timing relationships between them. Very
useful for figuring out what a circuit is doing.
> 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

If you can dump an EPROM, then, given the appropriate programmer, you can
dump anything else - it's the same process. Stick in the chip and hit
'read' :-)

> 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!

Don't worry. Post the problems here, and I'm sure somebody can help you
out. It's a little difficult talking you through a repair remotely, but it
can be done.

[QD vs HD]
> 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

You were lucky. I've had a lot of problems trying this. In fact, a _good_
(branded) DD disk may well be a better bet.

> 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.

> > 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...

Yes, I was talking about either classic peripherals (Sanders printers,
Versatec electrostatic plotters, paper tape stuff, card readers, etc),
peripherals for classic computers (1541's, etc), or peripherals used for
restoring classic computers (paper tape readers linked to PC's,etc). It's
obvious that Windows printing problems don't (in general) belong here.

> 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

Well, a combination of reading and experimentation. You'll come up
against a large range of circuits when you seriously get into restoration
- everything from 1000 gate+ digital systems with obscure timing faults,
to switch mode PSUs, to monitors, to electromechanical stuff, etc.

Most faults seem to be PSU/monitor related, thankfully. Books on TV repair
exist, and many are very good. The circuits used in TVs are similar to
those used in computers/monitors, and the same repair tricks work. The
monthly magazine 'Television' (available in the UK) taught me how to fix
power supplies.

> buy stuff that works? I don't spend a whole lot of time working on

Repairing them is half the fun...

> this stuff and when I do I get a sneaking suspicion that I'm not as
> smart as I think I am.
> Later,
> Bill

The gates in my computer are AND,OR and NOT, not Bill
Received on Thu May 22 1997 - 11:43:58 BST

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