I found something very interesting
The cost down. Toyota's way
Look at the photo below. This is the ECU for Celsior UCF21 engine 1UZ-FE.
There exist gold plated pins and non plated pins. I laughed looking at this.
The expensive car Celsior even has this type of cost downs or cost cuts.
As I checked signals of each pin, I began to realize that Toyota was very smart.
Those non plated pins do not handle sensing signals. Most of them just handle
bigger current or they are ground lines. Those are the reason why they dare do
not use gold at every pin. I would say they are very smart. Another smart way in
the printed circuit board is there is no switching power circuit. All the regulators
to obtain the logic circuit voltages are series regulators. There is no inductors for
a switching as is shown below. This consumes energy more and dissipates
more power and heat but it does not generates big ripple currents and
electrolytic capacitors last longer. ECUs should not use switching power unit
inside to obtain lower voltages for logic circuits and sensing signal circuits
without a sufficient additional countermeasure. The switching power supply
also generates the electro-magnetic noise and this also affects sensing circuits.
Toyota is smart too in this field.
Upper side.
Bottom side.
You can notice some area of the housings are smoked. Usually this type of
smoking is caused by a heat or a static discharge. My initial purpose to see
designed it.
Without doing much analysis, I could easily assume the reason why the ECU
malfunctions at lower voltage. One of the resister was burnt some and the
resistance was increased. Due to the higher resistance, the series voltage
regulator could not supply enough voltage to logic circuits when supplied
original voltage was not high enough. The photo below is the lower left corner
of the ECU board and the actual resistor burnt is indicated by a yellow arrow
(R862).
Compared with another similar type of the resistor R021 which is indicated
by a purple arrow located upper part of the photo, the color is totally different,
as you see. A resistor which uses oxidized metal film is strong against a heat
but you have to be careful when used for a long time. The heat damages the film
a little by little and the resistance increases. If Toyota have paid the attention
more to this and used a bigger resistor, I wouldn't have chance to notice this
and thought they were realy smart. Anyway the resistance change improved
the performance at lower voltage.
