Fixing a timing light
The broken Timing light
The label attached
I was asked to fix a timing light shown above when I was visiting a shop owner
who runs a Porsche repair shop called the Garage Neunmeister or in
Japanese ガレージノインマイスター. I knew he had a good skill in electronics
affairs but he was too busy to fix it. The timing light does not require the 12V
from the car battery. It has two UM-1 batteries inside and you can use it at
anywhere. Many German cars have batteries away from the engine
compartment room and you sometimes encounter a problem when you need
12V supply from the battery. For an example good old Porsches have batteries
in the front and the engine behind the seat. This timing light is convenient to
check Porsches.
The board inside and broken Transistors
As I saw the inside, there were two push-pull transistors shown above. Checking
the resistance between + and – terminals of the battery, I found it was less than
1 Ohm. Using an external DC power supply unit which had a built in current
limiter, I supplied DC 3V but it quickly shut off. The current limitter set to 0.5A
worked. Every time I increased the setting for 0.1A each up, it always shut off
and I gaved up supplying. Using a circuit tester with the resistance mode, I
checked the continuity of the two semi-power transistors used for the inverter
to get 300V or more from 3V. One transistor showed almost 0 Ohm between
the collector and the emitter. The other showed some resistance but it was
also semi-shorted.
Broken and removed 2 transistors 2SB405
The silk printed on the board said 2SB324 but the actual transistors used were
2SB405. Both 2SB324 and 2SB405 were used for transistor radios back in
60s and early 70s to get the out power for 500mw or so from 3-4.5V DC. Now
they are completely obsolete and you can not find them at major parts selling
companies. The shop owner helped me to find a place where 2SB324 was
available. It was the Bonton Corp in Osu Nagoya and I bought two of them.
The Bonton Corp carries many different types of semiconductors and
electronics devices. I actually have bought FETs the other day and fixed a
power supply unit for a Mac G4 owned by a friend of mine. You can see it here.
The reciept for two 2SB324s
Anyway after replacing two transistors, the timing light began to work well as
far as I checked it at my work bench using a pulse generator as a trigger
signal applying 30mA peak current to the pick up sensor. I am sure this works
well for the actual Porsche cars.
