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SERVICEMAN'S LOG
It took longer but it cost less
Security systems aren’t my normal run-ofthe-mill fare and one that I recently
encountered caused a few hassles. My other
big hassle this month concerned a manual
with a wiring error. And from New Zealand
I have a story about an 11kV power line
which tangled with the 230V supply.
My first story this month is about
time-lapse video recorder security
systems. Rather than scan continuously at the usual 25 frames per second,
they take a single picture every few
seconds.
These expensive high-technology
systems are fast becoming superseded. They are being replaced by lower
cost PIR (passive infrared detectors)
and add-on security kits for ordinary
video recorders, which are activated
only when movement is detected.
Most older time-lapse systems
cost around $2000 and are designed
to run continuously, recording up to
720 hours on one tape. Obviously,
they require regular maintenance
and most are supplied with clocks to
remind busy security control rooms
that it is time for a service every 1000
hours. Nevertheless, they inevitably
don’t bother with this until something
actually fails.
An urgent job
So it happened recently that a
local security company brought in a
Sanyo TLS-1000P recorder, complaining that it wouldn’t play and that it
chewed tapes. The security officer
who dropped it in said that the job
was urgent but the manager of the
company wanted a quote first. “Well,
it’s either urgent or you want a quote;
which is it?”, I replied. He called the
manager, a man named Bob, on his
mobile phone.
“Look”, Bob said, “the machine
28 Silicon Chip
is about 10 years old” (he was right
about that). “Is it worth fixing and if
so, how much?”
He told me that he really didn’t
want to go to the expense of replacing
it and in the end we agreed to go ahead
with the repair, up to a limit of $300.
Because the job was urgent, I attacked it straight away. First, I noticed
that the hour meter on the front panel
was showing 10,000 hours or full
scale deflection. This timer uses a
mercury column inside a 3AG fuse
which is permanently connected to
the switched 12V rail.
I have absolutely no idea how it
works or how to reset it; perhaps it has
to be plugged in upside down? What
I do know is that it isn’t available as
a spare part any more.
Anyway, after all this time, it was
due for a major service in anyone’s
language.
The second thing I noticed was
that it didn’t want to accept tapes. I
removed the covers and saw the major
problem immediately – the capstan
motor belt to the reel idler had bro-
Sets Covered This Month
•
Sanyo TLS-1000P time-lapse
video recorder
•
•
Sharp V1 Stereo A-V System
Sanyo Model C14ZA25 colour
TV set
ken and all the other belts looked in
a sorry state.
A new belt kit was fitted and this
time the tape went in straight away
and all the main functions appeared
to work OK. However, when I tried to
eject the tape, it didn’t want to.
Each time the recorder is switched
off at the power point and switched
back on, the letter “P” appears to indicate a power failure. The recorder
then has to be reset. When I did this,
the tape ejected properly. I then tested
it a number of times and it worked
faultlessly.
Having solved the main problem, I
cleaned the rest of the machine and
checked all the items listed in the
maintenance table. I replaced a few
suspect or worn parts but despite its
high usage, it really wasn’t in bad
nick.
Noisy mode select switch
When I had finished, I put the tape
in again to test it and once again the
set seemed unsure as to whether to
accept it or not. I felt sure this was
due to a noisy mode select switch
and gave it a good squirt of switch
lubricant. After that, it worked like a
Swiss watch.
The switch obviously had to be
replaced and so I ordered a new one
from Sanyo, only to be told that it
was no longer available – after all,
the set was manufactured in 1989!
As the mechanism is similar to the
VHR3500 and VHR3700 VCRs, I
wondered whether the part number
had changed but a quick check soon
showed it hadn’t. Fortunately, I decided to look through my local parts
supplier’s catalog and noticed from
the pictures that he had genuine new
ones in stock and so I ordered one.
It arrived the next day, just as the
old one was playing up again. Anyway, I managed to get a tape in so that
I could align the switch to its notch
position. I then turned the machine
off before unscrewing and unsolder-
new switch and had to check the part
number from the catalog. It was while
the catalog was opened that I noticed
a switch that looked exactly the same
on the adjacent page but with an entirely different part number. It was
this new switch that finally put
the problem to bed.
Bob wasn’t too happy with
how long all this had taken but
calmed down when he found
out that the bill was a good
deal less than he had been
prepared to pay.
The Sharp stereo A-V
system
ing the switch terminals from the PC
board. The new one was just as easy
to fit and no further adjustment was
necessary.
Unfortunately, when I finally reapplied power, it still wouldn’t eject. I
checked all the other functions which
were fine but, in the eject mode, the
loading motor turned until the front
(or “flont”, as the manual spells it)
loading gear engaged with the capstan
motor. And that’s as far as it got – the
motor wouldn’t turn at all.
It was then I noticed that the surface-mounted fish-oil capacitors on
the stator board were leaking. Aha!
These looked like likely suspects. After cleaning up the corrosion, the only
problem was replacing them with
small enough substitutes. However,
after all that effort, when I was sure I
was home and hosed, I was shocked
to find that it still wouldn’t eject.
Time for thinking
The moment I was dreading had
arrived – I was actually going to have
to get technical. I had already established that the capstan motor really
was OK, as it worked in all functions
except eject – it just wasn’t being
switched on.
It wasn’t easy to work out which
wires were responsible for switching
on the capstan motor from the servo
and syscon circuits so I decided to
start with the mode select switch
which deter
mines, via the loading
motor, the control of all the various
functions.
I established that the eject and
cassette-in modes occurred when the
switch was in the “d” position, when
the truth table gave a zero for the Data
1 and 2 buslines and a 1 for Data 0.
The switch was actually built with
four connectors which were, from
left to right: common, Data 2, Data 0
and Data 1. As a result, I expected to
see 5V on the third switch terminal
(or leg) only.
However, this wasn’t the case. Instead, legs 1, 2, and 4 were all high
and leg 3 low – a mirror image! At
first, I put this down to the switch not
quite being in alignment so I checked
it again – it was perfect.
I then confirmed that all the other
functions in the truth table were correct. I checked the DC resistance but
all I could come up with was that there
was something wrong with the “d”
position, especially when compared
with the original switch. Eventually,
I came to the conclusion that the new
switch was faulty and so I refitted
the original while I ordered another.
And after all that messing about, the
original now worked perfectly.
Now I must emphasise that the two
switches looked identical, because the
riddle was solved when I reordered a
My next story is about Mr Wilson,
a customer who has retired. About 10
years ago, he treated himself to what
was close to the top of the market;
a complete Sharp V1 stereo system.
This consisted of a modular hifi audio
unit with an unusual two-side linear
tracking record turntable (yes, it had
two pickup arms) and a remote control system – all heavy stuff in the late
1980s. Matching this, and connected
to it, was a 63cm stereo monitor-style
TV set and a hifi video recorder, the
whole lot mounted in a custom-made
shelving system.
The thing that really dates it all
now is the colour which was silver.
Nowadays you can have any colour
you want, as long as it is charcoal
grey or black.
Not long after Mr Wilson acquired
the pride of his life, it was damaged
by lightning. Although everything
else was fixed, the VCR was deemed
to be a write-off and so his insurance
company gave him the go-ahead to
get a new one. Naturally, he chose
another Sharp, this time a VC-6F3X.
Unfortunately, this model was in
black and no longer matched the rest
of his system but he appreciated the
additional features it offered compared to the VC-5F3X that had been
destroyed.
Recently, he brought it in for a
service as it was chewing tape and
needed new belts and an idler. All this
was straightforward and everything
was going to plan until I decided to
blow out the accumulated dust with
an air compressor. This required only
a gentle wave of the air-gun all over
to bring it back to a clean state. This
done, I confidently boxed it all up
and put it aside for soak testing before
completing the paperwork.
JUNE 1999 29
Imagine my horror when I switched
it on and found that I had lost all the
sound in both the play and EE modes
and that the LED meter display was
no longer functioning. Trying not to
panic, I opened it again and checked
all the plugs and sockets to see if
I had accidentally pulled any out.
But no, and there was absolutely no
sound coming out, not even from the
AV output or the headphone socket.
The only clue that anything at all was
happening in the audio chain was that
the stereo LED indicator still came on
for each channel.
The picture itself was great. This all
indicated that the audio signal must
be reaching the stereo decoder, so I
decided to start investigating PWB-1,
which was the top board and is easy
to access. Using my amplifier probe,
I was able to trace the audio signal all
the way up to the Input Tuner/Line
analog switch (IC6101). This device
is a TC4066 which is sometimes unreliable but fortunately easy to obtain.
The sound went all the way to
pins 4 and 8 but no further. Similarly, sound injected into the AV input
reached pins 1 and 11, so with a small
flat bladed screwdriver I shorted pins
1 & 2, pins 3 & 4, pins 10 & 11 and
30 Silicon Chip
pins 8 & 9 in turn but there was still
no sound. I was about to replace the IC
itself when I decided that it wouldn’t
hurt to be a bit more technical and
check a few voltages.
First, I checked the switching signals on pins 5 & 6 and pins 12 & 13
with a voltmeter to find nothing there.
I then checked the +12V supply (Vcc)
on pin 14 but this was absent also.
At last I was onto something. All
I had to do now was trace this 12V
rail to its source and find out why
it had disappeared. Of course, I was
still expecting something like a loose
plug or a switch parked in the wrong
position.
The 12V rail comes in on plug 1M2
which comes from BA11. As there is a
large wiring harness, where was BA11
situated? Simple, look at the wiring
diagram and sure enough it is shown
coming from PWB-B, the audio board.
But, in reality, it doesn’t. It took
nearly half an hour to discover that
this is an error in the schematic diagram. Instead, the 12V rail actually
comes from PWB-F, which is in a completely different location underneath
board PWB-1 instead of a wired audio
module on top of PWB-A (the manual
is not very forthcoming with infor-
mation about each board’s location).
Anyway, back to PWB-F. The 12V
source was Q6311, which was part of
a switchable regulator circuit whose
source was AT17V from BD-1, which
was connected to plug AS1 on main
board PWB-A.
Did I mention that access to this
board wasn’t easy? Well, it wasn’t – I
had already visited it once in the
mistaken belief I was going to PWB-B
and had only just put it all back when
out it had to come again.
The circuit for PWB-A is drawn out
over two full A3 pages, so it took a
little while to work out that the 17V
rail comes in on AF7 from the power
supply PD-1. This time I had the 17V
so there was a break between the two
plugs.
Using a voltmeter, I found that the
17V disappeared about 25mm from
AF7 and never reached AC1, AW1
and AS1. In fact, it looked as though a
link was open circuit. Unfortunately,
the link could not be seen from the
component side as the plastic cabinet
protruded over this area – not to mention the wiring harness to six plugs
in the vicinity.
And so I was forced to remove the
main board PWB-A. This is a major
undertaking involving screws, clips,
wires and an awful lot of swearing.
Eventually, I had the assembly and its
three daughter boards and tuner out
on the bench. A quick inspection of
the area involving the link (357) soon
cleared up the mystery.
There was a spot about 25mm in
diameter of severe green, black and
white staining, where corrosion had
taken place from an unidentified toxic
liquid. After cleaning off the debris
with every solvent known to man,
I could see that the link had in fact
disappeared completely, leaving tiny
fragments in the pigtail holes to the
PC board. After replacing the link and
cursing some more while I got it back
together again, I found (to my relief)
that everything now worked properly.
But how did all this happen? How
did a small amount of liquid get
into this location without touching
anything else, especially as the lid
and two other boards overhang this
area. Well, I can only surmise that it
dripped down the side of the plastic
casing, even though there were no
other marks. It guess that it could have
been water from a pot plant and but
why did it only decide to fail when I
used the air-gun?
I can only put it down to Murphy’s
law and move on. The really tricky
part was explaining all this to Mr
Wilson.
Kiwi power
And now for a change, here is a
contribution from a fellow serviceman
– S. W. in Hamilton, New Zealand. I
well remember reporting a similar
catastrophe that occurred here some
years ago, on the NSW South Coast .
Anyway, here’s S. W.’s story.
I was awoken early one morning by
a loud bang. Being of the cautious nature where loud bangs are concerned,
I made an attempt to determine the
source. It was a wild, stormy night, so
the first thing that came to mind was
the power. Everything in the house
was functioning OK and I checked
the meter and distribution boards.
Everything appeared to be in order,
so I went back to bed.
Later that day, I had a run of dead
appliances in for repair. It turned out
that a tree had fallen on the 11kV lines
that feed our area and brought them
down on the 230V lines underneath,
sending 11kV through everyone’s
houses and businesses. It was all very
messy but I got off scot free – technician’s luck, I guess!
Most of the appliances were TV
sets, followed by microwave ovens,
surge protection devices of the plugin variety, and stereo systems. In the
majority of TV sets, the mains fuse
had exploded into a molten mess and
the current limiting resistor (usually
5W or 7W wirewound) in the power
supply had simply gone open circuit.
This is interesting, given that these
components are on the other (appliance) side of the mains switch and
that these sets were not turned on at
the time. In every case, the high voltage had jumped the switch contacts
and into the circuit. Several sets also
lost chopper transistors and bridge
rectifiers or sets of diodes on the input
side of the power supply.
Some TV sets and almost every
microwave oven had varistors fitted
on the mains input filter boards.
These had all suffered and bits of the
varistors were found scattered in all
directions.
One of the TV sets was a National,
which was imported from overseas
and had an auto-adjusting supply
(110V-230V). It must have had a
hernia when it saw 11kV and it took
out the current limiting resistor, four
diodes and a Triac.
JUNE 1999 31
Serviceman’s Log – continued
The surge protectors were deemed
write-offs; it was cheaper to buy new
ones than to repair the dead ones. The
microwave ovens suffered varying
degrees of damage. In addition to
the faults listed above, several ovens
had the primary winding on the low
voltage transformer destroyed.
The stereo systems had tracks
blown off the PCBs and some lost
varistors as well. It is interesting to
see that more and more equipment
is now being fitted with varistors as
a form of spike suppression.
The damage to equipment was fairly limited in this instance, due to the
surge being spread over a wide area.
I have seen the results of a similar
situation involving just one rural road
where the same thing happened and
suffice it to say, there was nothing
left of the gear. It had just vaporised.
The real damage was caused by
the meter boxes being blown off the
outside walls of the houses and landing some 5-6 metres away. Inside the
houses, distribution boards caught fire
and set the interior alight.
Red herring
But back to the present and an encounter which I’ve called “The Red
Herring”. Later that week, a Sanyo
34cm model C14ZA25 came in. The
owner said that it had stopped working the night of the storm and he’d
taken it to another serviceman to
have it looked at. When he’d gone to
pick it up he was told that the price
t
Shop soiled bu
!
HALF PRICE
was in the region of $120. He wasn’t
prepared to pay that much and the
serviceman concerned “took the parts
out that he’d replaced” and gave the
set back to the customer.
I agreed to take the job on the theory
that the removed parts would be easy
to identify and it would cut down the
amount of work I had to do.
The following day, I opened it up
and inspected the underside of the
PC board. R502, a 3.9Ω 6W resistor
in the power supply, had been taken
out and the solder around a blank
area marked as transformer T581 had
also been disturbed. But there was no
actual transformer on the board.
A check of the rest of the board
showed that no other parts had been
replaced. At that stage, I remembered
the price that he’d been quoted and
came to the conclusion that the transformer must have made up the bulk
of the cost. I rang the local Sanyo
parts supplier to check the cost of a
replacement transformer, only to be
told that he could find no reference
to T581 in that particular set.
I went back to the service manual
and opened it to the inside cover
which shows the basic set layout (not
the circuit). And right there in the
power supply section was T581. It
is shown as a small step-down transformer, used to supply the low voltage
parts of the circuitry when the set is
in the stand-by mode.
It seemed logical that it could have
failed, as it would be connected di-
rectly across the mains input to the
set. The front cover of the manual
specifically says “New Zealand” in
brackets under the model number so
I knew I wasn’t looking at a universal
manual or a copy of a manual for a
different market.
I was still not satisfied and called
Sanyo’s head office only to be told
that they, too, could find no reference
to a T581.
“But it’s shown in the manual”, I
said.
“Hmmm, so it is”, came the reply.
I went back to the manual and took
a look at the circuit diagram proper.
And surprise, surprise – there was
no sight of T581. Now I was really
confused. It appeared as if it had been
replaced, it was in the layout but not
in the circuit diagram, and no one
could reference it.
I put the set to one side while I
worked on other jobs and when I
came back to it, decided to have another look at the PC board. On closer
inspection, I soon discovered that
the tracks that led from what would
be the secondary side of the transformer weren’t actually connected to
anything! It was definitely a furphy! I
replaced the 3.9Ω resistor and the set
sprang to life.
In hindsight, the solder on the holes
marked for T581 might have been
disturbed purposely to throw the next
poor bloke who looked at the set right
off the trail. It certainly worked!
In the end, the only part that had to
be replaced was a 75 cent resistor. The
customer was more than happy with
the bill and I am a bit more wary of
service manuals and red herrings! SC
14 Model Railway Projects
THE PROJECTS: LED Flasher; Railpower Walkaround Throttle; SteamSound Simulator;
Diesel Sound Generator; Fluorescent Light Simulator; IR Remote Controlled Throttle;
Track Tester; Single Chip Sound Recorder; Three Simple Projects (Train Controller,
Traffic Lights Simulator & Points Controller); Level Crossing Detector; Sound & Lights
For Level Crossings; Diesel Sound Simulator.
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