> > > 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.
If the TV has an isolated chassis (even some modern ones have the chassis
connected to the AC line!), then you can feed composite video in after the
video detector. A service manual for the TV and/or data sheets on the
chips in it will indicate a likely point for this.
On the other hand, very few home computers use need the bandwidth, so it's
easier to use a UHF modulator if you're feeding a TV from a composite
source or a tuner board (ripped from an old VCR) if you want to drive a
composite monitor from a home computer TV output. Of course you can nearly
always find signals inside the home computer that are either composite
video or that can be trivially combined to make composite video.
Some people like to keep their classics in factory condition, but I
personally don't mind simple reversably modifications if it makes the
machine more useful.
>
> 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
That's exactly the point. I'd not forget the nth harmonic tuning caps if I
had the chassis in front of me, but I might well do so in a How-to. Ditto
things like checking for shorts on the LV lines produced from the flyback
(which often feed half the stages in the monitor)
> 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.
I was planning on removing the pin altogether and letting the head
carriage move freely over the leadscrew. Then fit a micrometer head and a
spring to pull the head assy agains the end of the micrometer. I should be
able to get about 1" of calibrated head movement.
> 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
Received on Tue Aug 19 1997 - 05:59:07 BST
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