But, it was still very useful and fun. I used both
scopes for automotive
diagnosis. For example, it isn't very easy to find out that the problem
with an alternator ("just replace the whole thing!") was a diode (three
phase rectification) without a scope.
Hmmm.. I think last time I had to diagnose an alternator fault, I
desoldered the 3 stator leads from the diode array (9 diodes making a
3-phase bride rectifier with 2 positive outputs, one to the battery and
one to the regulator/field circuit) and then tested the diodes with an
ohmmeter. Removing the stator windings elimnated sneak paths through
those (and indicentally let me use a 'megger' on the stator to check the
insulation, somethinbg I wouldn't risk with the diodes connected). Of
course if a diode had been shorted, it would have probably caused
incorrect tests on the some of the otehrs, but if a diode was shorted I'd
have to tear the recifier pack apaart anyway.
Incidentally, (and this is more off-topic than usual), the Land Rover
series 3 workshop manual has a good _component level_ description of the
you want to align floppy drives (and nothing else), I would
try to find a thing called a 'Microtest'. It's a box containing an ADC
and a microcontorller that links to a PC serial port (_Any_ PC with a
floppy controller and a serial port, I think you need 256k RAM and any
display adapter, even MDA). You link up the drive under test as drive B
on the PC, and run the software that comes with the microtest. Then
select the drive from the menu (and there's every one that _I've_ ever
wanted to work on), it drwas a picture of the drive PCB (using IBM
line-drawing characters) and tells you where to conenct 5 clip-leads from
the ADC box. Then put in a standard analogue alingment disk and it will
tell you how far off-track you are, if the track 0 sensor is correctly
positioned, and so on.
That sounds sweet, and likely out of my price range.
When new, it was very expensive. I was lucky enough to be given one
'since you're the last person alive who actually repairs floppy drives'.
I then modified an Amstrad PPC640 laptop by removing the non-original
second drive and replacing it with a DC37 connector on a blanking plate
so I could cable up my drive-under-test to the Amstrad. As I said the
Microtest software runs on _any_ IBM compatbile, even a 5150.
I've not seen a Microtest on E-bay ever, but then I've not looked for
one. If one did turn up it would be small enough to ship, and doesn't
depend on amins voltage or frequency (the microcontroller box draws power
from the handshake lines on the serial port).
I liked using the Dysan Digital Diagnostic Disk, and wrote some code for
additional unsupported machines, but I could never shake the feeling that
I wasn't able to do as good a job as an analog alignment.
That's one good thing about the Microtest, it uses an analogue alignment
In college, I wanted to learn electronics, to design a
few toys with
integrated circuits, and understand the computer internals, but was always
I did juust that. Of course it had nothing to do with my course, but I
found invenstigating the Philips P850 back in my room to be a lot more
interesting that quantum mechnaics. Probably explains why I nearly failed
busy with other stuff, and the college required
multiple semesters of TUBE
electronics before getting to transistors, and only got to ICs in the
final "advanced topics" course.
Learning about valves (or at least bipolar trasnsitors and FETs) first is
proabably not a bad idea. Valves and FETs behave remaarkably similarly, BTW.
What an idiot I was. NOW where can I find a fun course for playing with
Hmmm.. For analouge (radio) use there was at least one such course in
Practical Wireless magazine in the 1950s (I mention this because I have
the issues somewhere). But I don't recomemnf it. The valve heater supply
came from a transformer, the HT (B+) came by half-wave rectifyuing the
mains. Which meant the metal chassis (uncased, this was an experimental
course after all) was connected to one sides of the mains. I would hope
And some of the simpler radios used headphones connected in the anode
circuit of a valve. Having a pair of headphones efectively connected to
the live side of the mains is too close to being an electric chair for my
But seriously, the best way to learn about valves is to p[ay with them.
Small valves are remarkaly forgiving of wiring errors (provided you don't
connect the B supply to the heaters!). There's a series of modern books
called the 'Impoverished Radio Experimentor' which covers making various
valve radios (including a superhet) using easy-to-dind components.