4 Aug
2006
4 Aug
'06
4:07 p.m.
--- Tony Duell <ard at p850ug1.demon.co.uk> wrote:
a
s
No problems there either, as I don't use a
monitor. I plug my A600 into my TV via the
RF cable. The picture quality is good enough
for me.
>
> > What would the "leaking decoupling capacitor"
> > look like, if that was the cause?
> It will look like any other capacitor. The
'leak'
is
> an internal
> electrical leak (a sort of weak short circuit).
> You'd have to find it by
> doing electrical tests.
>
> > Which is the capacitor? Anyone know?
> The thing about decoupling capacitors is
that they
> provide a local source
> of energy for the various chips, thus avoiding the
> voltage drop due to
> the resistance, and more particularly the
> inductance, of the supply
> connections. Therefore there is one (or more) next
> to each chip. And
> there's no way _anyone_ can tell you which has
> failed without doing more
> tests.
Ahhh, ok.
> -tony
> > > Probably best you didn't get the
16, as it's
> > inferior to the 12!
> Come again? The 16 has a 68000 processor
board (as
> well as the Z80) and
> runs Xenix (along with TRS-DOS and CP/M). The mode
l
> 12 is a Z80 only, and
> runs CP/M and TRS-DOS, although I belive the 68K
> board can be added later.
> > The 12 was actually made later than
the 16
> > and supports various modes making it
> > compatible with 16 and 4 (?) software
> > (and hardware?). Infact I think the Model 12
> I would be very suprised if the Model 12
could use
> Model 4 hardware or
> software. You certainly can't directly read M4 dis
ks
> in an M12 (due to
> the fact the former uses 5.25" disks, the latter
> 8"), for example.
> -tony
I'm relatively new to the TRS-80, and can
only go by what I have read in the issues
of 80 Microcomputing I have.
You, on the other hand, clearly are an expert
compared to myself.
Regards,
Andrew B
aliensrcooluk at yahoo.co.uk
> > I
figured (as you would) that my harddrive
> Actually, I might not. My first reaction
would
be
to
Note I said 'my first reaction'. I am something of stick a voltmeter on
the power lines.
errr... no voltimeter here, nor do i have a clue
where to buy one from (or how to use one). hardware type...
That said, I do feel that if you're going to run a
classic computer (as
opposed to running the software on an emulator),
then you are going to
have to learn a little bit about hardware and do
your own repairs. I make
no secret of the fact that I totally object to
making essentially random
changes (so-called 'board swapping') in the hope t
he
machine will work
again. I feel the only way to keep one of these
machines -- in fact any
machine -- working is to make measurements, figure
out what the problem
is, and then correct it. The first 2 stages should
take a lot longer than
the last. If you're spending most of your time
changing parts, you're
probably going about it in the wrong way.
As regards getting a meter, Maplin Electronics, RS
Components
(http://www.rswww.com) and Farnell
(http://www.farnell.com) all sell
them. Personally, I find the best multimeters
(combined
voltmeter/ammeter/ohmmeter) are made by Fluke, and
that's what I would
buy. Problem is they don't come cheap.
Realistically, you can probably
get away with a much cheaper (and less accurate)
instrument for this sort
of work.
I have no idea what your background/knowledge is.
A
good book on general
electronics is 'The Art of Electronics' by Horrowi
tz
and Hill, but that
might be rather advanced for you at this stage. Al
as
I don't know any
more introductory books than that.
As far as electronics go, it's practically zero.
I know how the CPU works and runs everything
, in theory, but I can't program in machine
language yet.
As for how the CPU and everything else works
physically, I don't really know anything, but
that is partly why I was keen to sign up
to this list.
> e
> > that to pass too much
> > current, but from my memory of the A500 circui
t,
I
Yes, I know. I don't have an A600 circuit diagram.
I
can't
think of any
obvious candidate.
Ahem, it's an A600 I own ;) am assuming the
basic design, at least around the PSU input
circuitry, is going to be
similar.
Ahh, I see.
> Have you tried running the machine with the
cover
> > off to see what is
> > getting hot? It might be something as simple a a
If the PSU is external (as I believe it is), then
there are no high
voltages in the computer itself. The PSU outputs
+5V, +12V, and -12V to
the computer. None of those voltages is high enoug
h
leaking
decoupling
capacitor.
I was planning too, but I had concerns about
being electricuted (spelling?) as I had never to give you a shock.
The most dangerous voltage you are likely to come
across in classic
computing is the mains or a 350V DC voltage produc
ed
by directly
rectifying the mains This turns up in what's calle
d
'Switch Mode Power
Supplies' (SMPSUs), and most computer supplies are
of this type. This
voltage is lethal. It's also likely to appear on
metal heatsinks, etc, in
such supplies. Don't work on one of those unless y
ou
really know what you
are doing.
Ok... no heat sinks in my A600 :)
Monitors are often claimed to contain lethal
voltages. Well, there's
mains (and most colour monitors use an SMPSU> circ
uit, so the hazard I've
just mentioned is there). But the even higher
voltages to the CRT are
generally only able to supply low currents, and ar
e
unlikely to be fatal.
Don't take risks, though, 25000V is darn unpleasan
t.
> snip <<
4 Aug
4 Aug
4:28 p.m.
I have no idea
what your background/knowledge is.
A
good book on general
electronics is 'The Art of Electronics' by Horrowi
tz
and Hill, but that
might be rather advanced for you at this stage. Al
as
I don't know any
more introductory books than that.
As far as electronics go, it's practically zero. I know how the CPU works and runs everything
, in theory, but I can't program in machine
language yet.
As for how the CPU and everything else works
physically, I don't really know anything, but
There are, unfortunaely, very few books that actually explain how the CPU
works. Most introductory hardware books explain things like the AND and
OR gats and flip-flops (don't worry if these terms mean nothing to you,
they're just the basic building blocks of computer circuits), and then
tell you the CPU exists. It's almost as if the CPU runs on some kind of
magic.
I can assure you that it doesn't, and that many older, simpler CPUs are
understandable at the gate level (or even the transistor level).
I know how _I_ learnt this stuff. I had already understood how to use
gates, flip-flops, etc. I mamaged to get the service manuals for an old
minicomputer, and I sat down for a couple of _months_ until I understood
it all. Of course back then there was no classiccmp list, I didn't have
anyone to ask. I was very much on my own.
that is partly why I was keen to sign up
to this list.
Eceellent!. Wanting to learn is the most important thing.
[Mains voltages etc]
voltage is
lethal. It's also likely to appear on
metal heatsinks, etc, in
such supplies. Don't work on one of those unless y
ou
really know what you
are doing.
Ok... no heat sinks in my A600 :) Monitors are often claimed to contain lethal
voltages. Well, there's
mains (and most colour monitors use an SMPSU> circ
uit, so the hazard I've
just mentioned is there). But the even higher
voltages to the CRT are
generally only able to supply low currents, and ar
e
unlikely to be fatal.
Don't take risks, though, 25000V is darn unpleasan
t.
6677
days inactive
6677
days old
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ard＠p850ug1.demon.co.uk