19 Aug
1997
19 Aug
'97
1:59 a.m.
> 4.
Classic Computer HOWTO's. I've been sitting at home for a week
> inventing things to do and started writing a how to document detailing
> drive alignment for various disk drives (not even close to ready yet).
> Anyway, seems like a cool idea for those of you who know how to do things
> to detail them in a howto and help improve everyone's know-how. People
> keep asking, for example, how to convert TV to composite output. If
> you've got nothing better to do ;).
Composite of any kind are no
difference TV has it too internally!
That would be wonderful when TV is very high quality tube/circuit
board to begin with. I think that someone would cut in byond the
Tuner for composite.
Aligning the drives is touch and go, once in a while I was
Given the alignment disk and a good 'scope it's a lot easier. You are not
looking for points either side of the right alignment - you adjust the
head position until the waveform looks right and clamp it up.
The latter is
actually a big problem. Most of the time I do things
'because that's obviously the thing to do' - i.e. I've done it many
times
before, and there are good reasons why (for example) the line output
transistor is the big one on the heatsink next to the flyback - but it's
difficult to remember this when you're writing a how-to.
There's those
crankerous capacitors too they does kill the HOT if the
signal is not cleaned up by those little capacitors. And capacitors area where ESR values is important. I'm trying to
get that ESR meter
too since I fix tons of switching PSU and monitors because it's so
inexpensive. About 60 USD and if anyone would like to, I have web
url address.
Anybody know a UK source for this. I do a lot of SMPS and monitor repairs
(both classic computers and modern ones), and it would be useful.
There's always ARD's quick test for large capacitors, which I hesitate to
mention, but which I used to sort out my 11/44 PSU when it was failing. It
goes like this :
1) Charge up the cap from a 9V battery, observing polarity. Connect it for
a few seconds then disconnect it.
2) Wait about 5 seconds
3) Short the capacitor terminals with a screwdriver. Anything over about
1000uF should make quite a spark. If it doesn't, it's either leaky or has
high ESR and should be replaced.
I had a 5000uF capacitor in the 11/44 that tested on my meter (using the
'balistic method' - connect it on to an analogue ohmmeter and see how
large the charging 'kick' is, compare to other capacitors) as about
4700uF, but which had a very high ESR.
I knew about that too, Those disks is too far
expensive for few fixes
run to pay off in due time. :)
It's not that bad. You only need 4 disks total - one of each size. They're
no more expensive than the other test gear you really should have.
If somebody could find a UK source of 8" alignment disks then I'd buy one
_now!_
I was lucky in a way. A place where I was working was decomissioning a lot
of PDP11 stuff, and of course I went (with a number of other people) to
rescue it all. The nice thing was that they'd done all their own repairs,
and they were also giving away the extender boards, test cables, _and_
alignment disks (RK05) and skewmaster 9-track alignment tapes. Needless to
say I grabbed all that stuff.
I was _given_ a Dysan 5.25" alignment disk a few months back :-).
One day
I'm going to rip apart an old 8" drive and put a micrometer on the
head assembly. I can then (hopefuly) record my own alignment disks using a
bit of simple electronics.
Well, better renew the mechanicals to assure tight
tolences! Screw
type does wear out especially the pin that rides in screw groove. Not that hard if you can grab the pin real good firmly
and pull and
rotate it 180 and reinstall. And lot of 3.5" especially new ones
are plain plastic bearings sliding on the smooth steel rods is the
worst wear. Those ones who uses bushings fares better.
All those oil and grease should be cheaned out and relubed again.
The service manual for my 3.5" drive (Teac FD235-something) specifies
lubrication instructions. I thought I was the only person to follow
them...
Jason D.
-tony