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SERVICEMAN'S LOG
(What) were the designers thinking?
One problem with being an engineer, a
serviceman, or similar is that whenever we
see something mechanical or electrical, we
immediately (and mostly subconsciously) assess
it for a range of criteria, such as what it is made
of and the methods used to manufacture it.
Or, in my case (especially in my younger, more
inquisitive days), how one could take it apart.
Basically, we can’t help but be analytical.
Let’s face it – everything we use,
buy or make has a design element to
it, and supposedly some theory sits
behind that design. However, I often
find myself quietly cursing the stupidity of some of these designs because
it appears that no actual thought processes have gone into them.
This phenomenon is by no means
modern; engineers have been bemoaning poor design for as long as there
have been people making things.
It might seem more prevalent these
days because of the number of YouTube channels dedicated to pulling
apart everything from tools and machinery to appliances and cars, often
for laughs. But they always seem to be
asking the age-old question: what was
the designer thinking?
I can reel off several examples for
you. I grew up with older British-made
cars and some of the decisions made
during the manufacture of those vehicles begs the same question.
To get the engine out of a Morris,
Austin, MG or Wolseley 1100/1300 for
example, you either have to have double-jointed hands the size of a small
child, cut an access hole in the passenger floor pan, or have an impossible-to-source specially-made spanner.
I had the motor in and out of my
1300 so many times we cut a hole in
the floor (replacing it with a suitable
access cover) and used a special spanner Dad made after seeing one at a garage in town.
And take the original Mini; iconic
though it is, one gets the distinct im62
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pression that they designed and built
the car and then discovered they’d left
nowhere for the battery, so it went in
the boot. There are many other examples and while I know these cars were
built down to a price, making life
more difficult for the poor
sod who inevitably
Australia’s electronics magazine
Dave Thompson
Items Covered This Month
•
•
Learning a painful lesson
HP 3585 spectrum analyser
repair
*Dave Thompson runs PC Anytime
in Christchurch, NZ.
Website: www.pcanytime.co.nz
Email: dave<at>pcanytime.co.nz
has to work on it is just not cricket.
Editor’s note: making fun of poor
British car design is like shooting
fish in a barrel. Who hasn’t heard of
Lucas Electrics, AKA the Prince of
Darkness? They were
truly innovative:
they invented
siliconchip.com.au
the intermittent wiper, the first selfdipping high-beam and they also produced a very potent anti-theft device:
their ignition systems. It’s difficult to
steal a car that won’t start!
A design dud in the kitchen
A while ago, we purchased a sandwich maker; one of those clam-shell
types that closes and bisects the sandwich while cooking it. In my opinion, this device has several design
problems.
Firstly, the top plastic cover protrudes out over the bottom section at
the rear of the maker, ostensibly to
cover the hot hinges and keep them
away from wayward hands.
But the steam produced while cooking is very effectively trapped by this
hollow, overhanging moulding. The
steam then condenses and drips down
onto the bench and power cable. We
have to put a folded paper towel or similar beneath it, to avoid pools of greasy
water forming under the back feet.
While this is no deal-breaker, it
clearly isn’t a good design. And that
isn’t the only problem, either. The
more significant failing is the fact that
no matter what brand of bread we buy,
none of the slices fit correctly.
The bread slices either fit entirely inside the cooking cavity and don’t make
contact with the edges, or they end up
with one edge sticking out the sides.
(Editor’s note: perhaps you are using
metric bread, and it was designed for
imperial? Try using a British Standard
Loaf and see if that fits.)
While the smaller slice might seem
the way to go, fillings (cheeses in particular) bleed copiously from any seam
that isn’t clamped and sealed by the
elements and then proceed to leak out
all over the rest of the machine and
the benchtop.
This leads us to another design flaw:
the gaps between the elements and the
case mouldings. From the first sandwich we made, these cavities fill up
with crumbs, cheese, water and anything else that might be cooked in the
appliance. After just a few months of
weekend-lunch use, this sandwich
maker was so filthy and impossible to
clean properly that my wife refused to
use it anymore.
Being the gentleman serviceman, I
took it to the workshop and stripped it
down to clean it out, and what a lovely
job that was!
It is generally pretty easy to take
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apart, except for the vain attempt by
the manufacturer to prevent me undoing four, pimple-bottomed Torx-style
“safety screws”.
But I did have to cut the connectorsecured power cables off to free the
bottom plastic case shell, as the power lead clamps to it with flying wires
connecting to the elements through a
small hole in the case.
Australia’s electronics magazine
The reason I went that far is because
the bottom half was almost completely covered with both greasy and rockhard melted cheese and breadcrumbs.
I had to chip some of it off with a
screwdriver. I used my heat gun to soften the baked-on gunk on the outside
of the case because it couldn’t be removed without otherwise damaging
the shiny plastic finish.
I would have expected this type of
mess after a year’s worth of use by a
family of five, but it seems a bit excessive for a few months use by two of us.
Of course, we could use a smaller
quantity of ingredients, but where’s the
delight in an empty toasted sandwich?
A quick visit to some big-box stores
with a pocket tape-measure confirmed
my suspicion that all similar sandwich makers have the same size cooking cavities as ours, or very close to
it. Has no sandwich-maker designer
ever purchased a loaf of bread at the
supermarket?
Perhaps there is a theoretical standard slice size, but if so, not many bakers adhere to it. If I designed a sandwich maker, I’d make it so that the
majority of everyday
bread slices fitted it
properly.
February 2019 63
Ah, the bad old days
Do you have any good servicing stories that you would like to share in The Serviceman column? If so, why not send those stories in to us?
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someone had knocked my hand away
with a bat.
When I pulled my hand in front
of my face, the top 5mm of my right
thumb was hanging by a thread, and
there was blood everywhere. Yikes! I
didn’t know what I’d done at the time,
and can’t recall how I got out, but I do
remember walking up to the guys in
the workshop by the hangar floor holding my hand out and telling them I
thought I might need the nurse!
It turns out that some bright spark
in a design department somewhere
had dreamed up a modification to
keep some equipment cool in the bay
and a 120mm steel-bladed cooling fan
had been fitted to the rear of one of
these racks on a previous maintenance
visit. I didn’t know it was there, and
the powers-that-be saw no need for a
safety cover for the fan because it was
mounted “out of the way”.
Now, modifications like this aren’t
just dreamed up by some bloke with
a hangover one Monday morning and
installed that afternoon.
This would have been thought
out and put through rigorous checks
and balances at the highest levels
by the manufacturer, or one of their
contractors. They would first see if
it was required, then ensure it was
implemented to the highest possible
standards.
This process also involves updating the very comprehensive manuals
that go with every aircraft; these huge
books document every nut, bolt, panel,
cable, washer, rivet, system, component and piece of equipment inside it,
along with all the specifications, circuit diagrams and schematics of literally everything on board.
Not one of the dozens of people involved in this design process thought
about installing a safety screen.
Any new addition to an aircraft, regardless of whether it is a plastic bung
for the end of a seat frame or a whole
new navigation system, is also rigorously tested – destructively and nondestructively – by the aircraft manufacturer and interested third-parties
before getting anywhere near a plane.
It can take many months, if not
years, before the information and parts
are eventually available to the endusers for implementation. Something
fell short here.
Inevitably, I had to take time off
work and the injury also caused me
to miss my final exams – which I had
Australia’s electronics magazine
siliconchip.com.au
A more severe example of designer
negligence harks back to my days as
an aircraft engineer. Actually, I was
technically still an apprentice at the
time, in my final year and just before
my final trade exams.
For those not familiar with widebodied aircraft, at least back in those
days, most of the major electronic
components are kept in a special area
called the E&E (Electronic and Equipment) bay.
Much of an aircraft’s radios, controllers, computers and various other components are packed into this space,
mounted in special racks and cabled
in with vast looms of wires strung from
the farthest reaches of the plane.
This room is accessible via a hatch
beneath the aircraft (sometimes from
inside as well) and it varies in size depending on the aircraft. The E&E bay
on a 737 is a lot smaller than that on
an A380. On some planes, I’d need a
step to boost me up enough to climb
in, while taller guys could often work
standing on the ground.
On the particular aircraft I was
working on then, an ageing Boeing
727, one of three then-used as transports by our Air Force (nothing but
the oldest and cheapest crates for our
boys!), the bay required me to climb
a special ladder to access it. As I was
of a smaller and skinnier physical size
back then, I got all the jobs the bigger
guys opted out of.
Being an apprentice also had a lot
to do with this, and apprentices usually got fun jobs like cleaning bird remains from the engines of aircraft that
had suffered bird strikes.
Bird strikes are rare (thank goodness!), but when they happened, the
task of cleaning the rear section of
the engine would be passed down the
chain of command until it hit the bottom – an apprentice.
As one of the guys said at the time,
“manure rolls downhill”; although
those are not the exact words that he
used.
You’d think that a seagull going
through all the turbines and vanes
spinning at thousands of RPM inside
those big jet engines would essentially
be vaporised. This is not the case, and
it is a particularly unpleasant task to
kneel in puddles of aviation fuel in a
confined and grimy metal tube scraping crispy bird remains from the sides
of the engine. It put me off chicken
for years.
Thankfully, as I moved up the pecking order (hah!), that job became a
younger apprentice’s problem.
Learning a painful lesson for
someone else
One job I did do a lot, just because I
was one of the smallest qualified guys,
was inspecting, cleaning and repairing
wiring looms inside the wing-tanks on
whatever plane needed it.
If you think there isn’t enough room
in the wing of a plane for a person to
work, you are mostly right; it is a very
tight and claustrophobic space, especially when decked out with all the
lights and breathing gear and carrying
special anti-static tools.
My foreman always swore that he’d
cut a hole in the skin of the wing if I
ever got stuck in there, but now I’m not
so sure he’d have kept that promise!
But I digress; I had work to do in this
727’s E&E bay, adding wires to an existing loom for some new component
going in. This required me to contort
myself into a flat position on my back
while curling around sideways to get
right in behind one of the racks so I
could crimp and terminate the wiring
into a Canon connector mounted on a
frame there.
It was tight and taxing work and
once again, because I was one of the
smaller guys, I got assigned to do this
type of thing a lot.
The problem wasn’t getting into position, but getting out again when my
arms were in behind the racks and my
feet hanging out the hole in the floor;
I didn’t have a lot to push against to
make my way out. I reached up to lever
myself against the back of the rack and
felt a sudden hard whack, as though
Servicing Stories Wanted
64
Silicon Chip
to sit later. I also had to play guitar at
a friend’s wedding that weekend and
did so painfully, with the pick taped
to my comically-large thumb bandage.
My right thumb is still shorter than
my left because the base doctor just
tore the damaged bit off and threw it
in the bin!
I recall it hurting, a lot, and it didn’t
help when several guys from the technical department came over and had a
look around before interviewing me,
claiming they never thought – and I
quote – that “anyone would be stupid enough to stick their hand in it”.
The only silver lining is that the
fan was running in the direction that
pushed my hand out, rather than simply ate it whole. A mesh screen was
eventually fitted and I’ll wager most
other fans fitted after that had one
too, regardless of where they were
situated.
I (and others) couldn’t believe this
mod had made its way right through
the testing and vetting process without
someone realising that having a highspeed steel cooling fan unshrouded
in a work environment might be a bit
of a health and safety issue. I mean,
we are talking about an industry that
is typically extremely paranoid about
every aspect of safety!
I’m guessing that the character sitting at a drawing board who originally dreamt this up, along with the people who subsequently signed off on it,
have never had a pair of overalls on or
wired a rack in an E&E bay. You just
can’t beat hands-on experience.
Even the grass is mocking me
And on another note, I recently purchased a new lawn mower, given it’s
the time of year when you can hear
the grass growing. It is a well-known,
dayglow yellow brand and I assumed
they’d know a thing or two about making lawnmowers.
However, when I tried it, even set
at the lowest blade position, the lawn
was still looking uncut. I like a short
lawn; not shaved earth, but preferably cut enough so I don’t have to do
it twice a week. All my old mowers
could cut this short but this one goes
no shorter than the industry standard
of 25mm.
I contemplated modifying the level
notches on the side, but even with the
deck scraping on the ground, the cut
was still far too long. The blade disc
is just too high in the deck. I ended
siliconchip.com.au
up removing the large, central bolt
holding the blade disc on and added
10mm of washer shims to the top-hat
style mounting plate before bolting it
all back on.
It now it cuts perfectly, but it begs
the question; did the guy who designed
this mower ever mow an actual lawn
with it?
HP 3585 spectrum analyser repair
A. L. S., of Turramurra, NSW, has
had one thing after another go wrong
with his 40-year-old Hewlett-Packard
spectrum analyser. But he’s obviously
very attached to it since he keeps on
fixing it each time. Here is what he
had to do to keep it going over the last
couple of years...
The HP 3585 Spectrum Analyser is
a very versatile instrument, covering
the frequency range of 20Hz to 40MHz
with a 3Hz resolution, making it useful
for both audio and RF applications. It
also has a built-in tracking generator.
Unlike most spectrum analysers
(which usually only tolerate tiny RF
signals), its input capabilities are
really good with a selectable input impedance of 50W, 75W or 1MW
and with 42V peak handling, which
is ideal for testing medium-power
audio amplifiers.
I purchased this one locally for a few
hundred dollars on eBay; that’s quite a
bargain when you consider that it was
more than $30,000 brand new in 1978.
Australia’s electronics magazine
To put that into perspective, it was the
same price as a Mercedes Benz 450SL!
My unit had a number of faults that
occurred over a two year period, so in
that respect, it’s probably about as reliable as an old Merc too.
First, some intermittent flashover
started happening in the CRT EHT
section, usually during periods of high
humidity, causing the CRT to eventually fail altogether. I noticed that the
LEDs on the front panel appeared to
still be operating normally and a quick
screen grab using a GPIB/USB connection proved that the instrument was
still fully functional, apart from the
lack of display.
Using the display (X & Y) BNC connections at the back of the instrument,
I was able to obtain a very good working display on a 20MHz analog oscilloscope set to X/Y mode, as shown in
the accompanying photo. This only
works with an old-fashioned CRO
though; most digital scopes are just
not fast enough to do this!
I used this arrangement for some
time while I waited for a surplus CRT
and EHT supply to arrive which I had
ordered from the internet. When they
finally came, I first had to turn the instrument upside-down, which was difficult because it weighs 40kg!
I removed the HT supply box to
take a closer look and to figure out
how to change the CRT and it did
not look easy. There was a fair old
February 2019 65
Circuit diagram for the motherboard of the HP 3585 from the second service manual (A41; page 192), which can be found here: www.ko4bb.com/getsimple/index.
php?id=manuals&dir=HP_Agilent
66
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Australia’s electronics magazine
amount of accumulated dust around
the EHT leads and components. This
was probably the cause of the sparks;
after a long spell of high humidity, the
dust absorbed enough water to become
conductive.
I cleaned everything out, including the interior of the EHT box, using rags and methylated spirits and
then dried it all out. Then I noticed a
small perspex cover which concealed
a 1A fuse and a quick check revealed
it had failed. I replaced it, thinking
that it would instantly blow again,
but magically the whole instrument
lit up and the CRT display was bright
and normal.
The instrument then functioned
well for a year. Then one day, it refused
to start up properly. All the LEDs on
the front panel lit up but nothing else
happened.
Switching the instrument off and
on a couple of times brought it to life
and that is how it operated for a few
months until finally, nothing happened at switch-on except for the front
panel lighting up. I left it for some time
to gather cobwebs because I had another HP 3585a which worked properly,
except its knobs, which meant that I
could not control the tracking generator amplitude.
Eventually, I decided to tackle the
fault by exchanging a few spare low
voltage regulator PCBs that I had obtained from the internet. There are
five of these in each instrument, so
I changed them one by one but that
didn’t cure the fault.
The service manual, which runs to
three volumes and 884 pages, points
out that one faulty board may be capable of damaging another so that the
end result might be several damaged
boards and this worried me a bit.
The output voltages from these
boards measured correctly and that
plus the fact that the five green status LEDs were all lit, suggested that
the power supply was functioning
correctly.
Again, I put the instrument aside,
fearing that the fault was too elusive,
and went back to the older working
instrument.
Some time later, I decided that I had
to throw it away or fix it. I decided to
substitute the PCBs from the working
unit and take a risk that I might end
up with damaged boards and have two
dud instruments.
There are about 24 boards in total,
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An analog oscilloscope was used temporarily as a replacement screen.
The inside of the spectrum analyser is packed with boards (24 in total).
The HP 3585 motherboard shown above, corresponding to the circuit diagram at
left. The 80-pin CPU (U13) is located under the large ribbed heatsink.
siliconchip.com.au
Australia’s electronics magazine
many of which are difficult to access,
so I just started at one end and replaced
the suspect boards with the good ones.
Rather than swap in one board,
check if it works and then swap it back,
I decided to move all the known-good
boards into the unit one by one, in case
two or more boards were faulty. Then
suddenly, after I replaced the central
processor board, everything came to
life again.
As it happened, I had a spare processor board on hand, amongst a set of
boards that I had previously purchased
from eBay for spares. It was horribly
dirty but the unit worked with it in
place, so I had two working instruments at last! But that is not the end
of the story.
Ironically, just as I was finishing this
story, a similar fault occurred and the
instrument would not start up, even
though some LEDs were flashing normally on the front panel. It came back
to life when I substituted the processor board (03585-66541) from “old
faithful”.
Apparently, I now have two dud
processor boards and there are none
to be had on the internet. The usual
parts sellers told me that they had sold
all their processor boards. I was back
to square one.
I tried to repair the faulty boards referring to the excellent repair manual;
I replaced all the electrolytic capacitors (and the other capacitors for good
measure) but nothing worked.
The voltages around the main ICs
all measure good but there are 23 of
them so replacing them would be a
massive undertaking, even if they
were available.
And then there is the main processor chip which is the size of my wallet and definitely not a standard item!
I found one internet seller that had
three dud HP 3585 analysers for sale.
He was asking $800-1,000 each for
shipping but the photo of the instrument showed a very dim glimmer
of a trace which indicated a healthy
processor board, so I asked him if he
would accept half price and pull out
the desired PCB and post it to me via
USPS for about $40.
After about 20 emails back and forth,
we finally came to an agreement on
price and the board arrived safely and
it actually worked. The reason for the
failure of these boards remain a mystery but I have kept the two dud boards
for future spares.
SC
February 2019 67
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