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Fixing an old tachometer

My local car shop owner asked me for a help. He was having a
problem with a non working tachometer used for a 93 Celica GT.
He has tried to replace the tachometer but it was totally
impossible to obtain any new or used one.

The car is 25 years old and the parts availability is now quite
low. But the car itself looks very new both inside and out.
The car was designed and made at the golden era of Toyota. 
The engine runs well too and he really wanted to fix the
tachometer expecting me to do it.

He quickly removed the cluster unit from the dashboard and
showed it to me although he was busy doing another project
when I visited.

Below is the rear view of it. The tachometer is held by 3
screws as is shown. Those 3 are also used for the terminals
to supply +12V, to connect to the ground and the RPM in signal
judging from traces and other components surrounded.
So removing those 3 screws makes it possible to remove
the tachometer unit from the cluster and check it at a bench.


イメージ 1


I connected the DC12V power supply to the cluster and applied
the 60Hz or 120Hz signals from a simple home made signal
generator. The reason why it is simple is that the signal
source is not generated inside but is getting the 60Hz energy
from the power company. It is consisting of a modified AC
adapter and a circuit to make square waves of 60Hz and
120Hz. A 60Hz square wave signal can drive the tachometer
to indicate 1800rpm and 120Hz, 3600rpm in case of a 4 cylinder
engine. Probably you may wonder why a power company's
60Hz can be used for the check of a tachometer. I will be
explaining it later.

As I checked the board behind the tachometer panel, there
were 2 electrolytic capacitors 10uF/25V. Those 2 had a
symbol mark of Matsushita. These days I have been
experiencing problems caused by aged Matsushita's
electrolytic capacitors. They were commonly dried up
badly. Of course electrolytic capacitors will dry up some
day in accordance with the Arrhenius equation, but
Matsushita's ones dry up quicker than other major
Japanese brands due to the reason that the rubber
becomes more brittle than others according to my
experience. Actually, I recently had a door's lock/unlock
problem on a 18 years old Subaru Pleo and it was caused
by old Matsushita's electrolytic capacitors. With these
my own experience, I dare removed those 2 capacitors
and replaced with new ones manufactured by Nippon
Chemion. Speaking of electrolytic capacitors, QAS capacitors
fabricated by Nichicon also end the life quicker than others
and auto mobile industries had some impact. One example is
the Celsior / LS400's ECU witten here below by a friend of mine.
https://www.clublexus.com/forums/ls-1st-and-2nd-gen-1990-2000/656360-all-my-crazy-lexus-issues-solved-ecu-leaking-capacitor.html

We have to be careful for aged electrolytic capacitors especially
the one with the QAS liquid inside and some company's one with
a rubber which becomes very hard like a plastic and brittle as
are like those 2 used for a Celica's tachometer.

イメージ 2


As I checked those removed two below using an ESR meter,
one showed more than 600ohms and the other infinity.
These were surely dead or almost so.

イメージ 3


After replacing capacitors, I checked the tachometer
applying 60Hz and 120Hz attaching the signal generator.

イメージ 4

イメージ 5

After installing the cluster unit to the dashboard, the shop
owner said, “It's working perfectly. Thanks for the help and
I'll take you to a dinner appreciating your efforts”.
I am counting on what he'll serve me.


イメージ 6

イメージ 7



Regarding the home made signal generator, originally

it was a AC adapter of a 6VDC. I added 2 rectifying

diodes inside to get the half-wave rectified waveform

and the full-wave rectified waveform. Using a Schmitt

trigger circuit, those are converted to square waves of

60Hzand 120Hz. A  4cycles of 4 cylinders engine's

revolution 1800rpm means 30rps and the engine ignites

2 times at each revolution. This means that there are

60 ignitions in 1 second. This is the reason why a power

company's 60Hz energy can drive the tachometer

1800rpm and the twice frequency 120Hz, 3600rpm.

This simple method is enough for us to check the

tachometer without buying an expensive signal

generator. This certainly is a poor man's method

but quite effective to check a tachometer as well

as a speedometer since 60Hz drives the speedometer

85km/H and 120Hz, 170km/H.


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This time, I was requested to fix a NEC PC-LL750F26B. It has a
CPU Core i7-2670QM and the memory 8GB. It's not very new
but it's too early to discard. As you see the photo below, it says
Core i7.
イメージ 1
                                             The label says, "CORE i7".

I have once experienced a short circuited problem of a ceramic
capacitor used for a NEC laptop at here.
https://blogs.yahoo.co.jp/mae_yas/11468574.html

As I have written above, there were many similar problems among
NEC PCs in the market. When one of ceramic capacitors used
for the bypass purpose is short circuited internally, it is not easy
to find out which one is failed since there are many other ceramic
capacitors in parallel with it.

The last time when I fixed the lap top NEC PC-LS150BS6W, I only
needed to use a multimeter which can read down to 0.01Ω to
find out the exact short circuited one since it showed the
resistance 0.01Ω smaller than others and rather easy to distinguish.

This time the symptom was completely no power. Nothing has
happened when the power button was pushed on. No LED nor no
screen lit as if the AC adapter / battery was dead. As I checked
the inside using a multimeter, I found the DC line for the primary
side of the CPU power block and others showed only 0.3 Ω or so.

The photo below shows the resistance at the power supply line.
It is close to the connector where the external AC adapter is
connected. It showed 0.30Ω to 0.33 Ω depending on the
pressure to apply to the capacitor's terminals. When the
photo below was taken, I had to hold the camera by my right
hand and my left hand was barely holing the 2 test leads.
I was not able to give terminals enough pressure and the
read out showed 0.33Ω.
イメージ 2
                                Showed 0.33Ω when leads barely touched

The lowest resistance
0.27Ω was found at the primary side of
CPU's power circuit. There are 4 ceramic capacitors very close
to each other and all of them showed 0.27Ω.
The photo below
shows the location where the lowest resistance was confirmed
and I connected wires to supply the current using a low voltage
DC power supply unit. As you see below there are 4 capacitors near
the red and white leads are soldered. All these are in parallel.
イメージ 3

Connecting a low voltage power supply unit, I used an infra-red
thermometer which area was warmer than others. 
イメージ 8

イメージ 9

I found that the primary side of the CPU power supply was warmer
than others and this explained why the resistance was lowest there.
I also determined which one out of 4 is failed. The voltage is 0.332V
and this does not go through semiconductors but can go through
resistors. So we can find the semi short-circuited capacitor easily.
There still existed 0.27Ω and this should heat up the capacitor.
Suppose the current is 1A, theoretically the power consumed
by the capacitor is given as follows
.
 P=I X I X 0.27
For an example, when I is 1A,
 P=1A X 1A X 0.27Ω
   =0.27W.

The actual low voltage DC power unit is as below.
イメージ 4

イメージ 5

The voltage of the unit is 1.256V when the nob is set minimum
and is still high for semiconductors. So I added 2 resistors in
parallel and a schottkey diode to limit the current and the
voltage. The resistor I used was 1.35Ω(2 X 2.7Ω parallel) and
this  limits the current up to 0.93A (1.256V/1.35Ω=0.93A).
The schottkey diode is EC31QS03L(Io 3A, Vrrm 30V, Vf 0.45V max)
to limit the voltage. In my application, the actual clamped
voltage is around 0.33V or so as you can see in the photo above.

When the output is open, the voltage is limited up to 0.33V and
the maximum current is limited 0.948A theoretically by resistors.
The capacitor had remaining resistance of 0.27Ω and the
maximum current should be limited 1.256V/1.35Ω + 0.27Ω ≒ 0.78A.

Applying the current, I touched the second capacitor from the
right side by my index finger, I felt some extra heat and confirmed
it was the culprit. Replacing it fixed the problem. The removed
capacitor  showed the resistance 0.27Ω. I had no idea to know
the original capacitance but judging from the application,
I dare used a 1uF ceramic capacitor manufactured by a Japanese
company Murata which I trust a lot.
イメージ 6

イメージ 7

Now the PC powers up and works well as it used to be.

I think I need to explain the low voltage power unit a bit more.
In addition to the DC power supply, I used external resistors
1.35Ω(2 X 2.7Ω parallel) to limit the current. The schottkey
diode was EC31QS03L(Io 3A, Vrrm 30V, Max Vf 0.45V) aiming
to limit the voltage. Adding these parts allowed me to supply
the DC to the main board without damaging semiconductors.
This is based on the theory "Fermi level".

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Fixing a clock spring

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Seethe photo above. It's a clock spring used for a Mitsubishi


ek-Wagon. It intermittently turned on the air bag warning light.


A local car shop owner needed to fix it quickly and he asked


me to help. He was in a hurry and also the customer didn't


want to spend any extra money to fix it except the labour charge.


As I inspected the flexible cable inside, I found a damaged part


as was shown in the photo below.

イメージ 2

Peeling off the surface some, I soldered it and attached a polyimide


tape to insulate and to make it possible to slide easily. The tape

also adds some strength to the cable.

イメージ 3

イメージ 4

After installing the clock spring unit to the steering column, there's


no more warning light. It seems to be OK just soldering the damaged


part. I'm wondering how long it holds the connection. The car is already

rather old and I think it would be OK till the car is sent to a junk yard.

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イメージ 1

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Although I'm not a professional car repair guy but I often have requests to
help to fix troubled cars by local shop owners these days. Why?
Because they expect me to fix cars that can't be fixed by mechanics.
They are not good at modern cars that are equipped with many electronics
controlling circuits.

Today I worked together with a shop owner who was having a hard time to fix
a Peugeot 307SW which is shown at the top photo.

The problem was the headlights that turn on / off randomly without touching
anything. As I searched the Net, I found there were many similar problems among
Peugeot and Citroen cars in different countries. I also found that most of
them needed to replace the whole unit called com200X to fix as is written at below.
The stalk is not sold separately and the whole unit is needed change.
http://www.peugeotcentral.co.uk/ftopic-12887.html

The Citroen C3 also uses the same unit and there are similar problems too.
https://citroenc3owners.com/citroen-c3-tips/the-com2000-or-steering-wheel-stalks-an-inside-look-t467.html

The headlights are designed to turn on when the communication is failed
between the com200X and the BSI unit, I understand. This is to inform the
user that the communication error is occurred. The cause of the
failed communication is mostly caused by the unusual signal from the stalk.
The best way to fix is to replace the com2003X/BSI unit. But these
costs some big money. So what we did was to disassemble the stalk
to check conditions of contacts and those were like the last photo.

Those contacts were badly clogged. The dark part was completely oxidized
and there existed some big resistances. After I cleaned contacts, I used a
pencil 6B to wipe off the oxidized surface as well as to fill scratches
with the graphite and carbon to reduce the resistance. I also used a
contact restorer. After the job, the resistance became almost 0Ω.
After doing these, we installed the unit to the car and checked the
functions. We found that the problem was completely gone without replacing t
he unit. The shop owner said,"We did it".

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Mowing machine out of use

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My mowing machine "Ryobi EKK-2100" stopped working
while I was mowing at my vegetable field the other day.
イメージ 1

イメージ 3

I tried to restart it but there was no luck at all. As I saw
the engine carefully, I found the priming pump cracked
a bit. It was absorbing the air and the gasoline was not
sent to the carburettor. The crack was getting bigger
and bigger as I pushed the bottom side and the gasoline
was leaking out
イメージ 2

Without the gas, the mowing machine has no idea to work.
All I needed to do was to replace the pump. But local
shops didn't have the pump at all.

Did I have to buy a new mowing machine?

No kidding! My wife said. She also added,”You always
fix anything except human beings. Why don't you try
to find it on the Net”.

I searched the Net and I found this below.
http://item.rakuten.co.jp/proplace/pp-1/
This costs 378 yen + shipping cost.

As I searched more and I found this below at the Yahoo
Auction. This is costing only 580 yen for 2 pieces including
the shipping cost. This looked nicer and I decided to
choose this and I ordered 2 pieces.
イメージ 4

2 days later, the parts arrived and I quickly installed one
and fixed the mowing machine.
イメージ 5

イメージ 6

Now it is back to life and working fine. I can resume the
mowing job now.

The seller seems to be running a gas station or something.
I found this below at the Yahoo Auction but the link below
may not effective every day.
http://page9.auctions.yahoo.co.jp/jp/auction/k197870034
May be you can find the part searching the name of

Primary pump WPV12-B.



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