Re: Does anyone here understand this?

Posted by sgtslag on Jun 17, 2013; 3:16am
URL: http://vintage-and-classic-hondas.81.s1.nabble.com/Does-anyone-here-understand-this-tp4042375p4042386.html

The 555 Timer Chip (pin out link), is a square-wave generator; in this setup, it outputs a single polarity (DC) square wave.  Pins 2, 6, and 7, all control the frequency, and the pulse width modulation -- how long the voltage is positive (on), or off (zero volts), which is known as duty cycle.

Pin 3 is the output of the chip, which drives the G connector on the HEI Module (link to sample), which pumps the current through the primary coil on the spark coil (the 555 Timer is a low current device, so it provides the control signal for the high amperage HEI Module):  the primary takes low voltage/high current, and transforms it into high voltage/low amperage, which causes a spark to jump the gap on the plug (the power remains the same:  Power/in = Power/out = Voltage x Current; the coil, a transformer, trades one quality up, while lowering the other quality, but power remains the same, due to conservation of energy -- there are minor losses due to heat).

Diode D1 makes sure that only positive voltage is applied to the Timer chip, IC1, which prevents it from being damaged.  Anything marked Electrolytic (Ca, C1), are polarity sensitive -- if you connect the Positive Lead (+) to the Ground/Negative pole of the battery, they will burn up, quickly.  Be careful when wiring them.  They are capacitors, which are used to filter AC ripple out of the power supplied to the Chip (C1), which can damage/interfere with IC1's operation.  Capacitor Ca provides timing (RC/Resistor-Capacitor time constant), it determines the timing of the square-wave output; the combination of R1 and VR1, determine the Resistor value of the RC time constant.  Diode D2 helps supply current to charge Ca, which plays a role in the timing.  The control, VR1, is like a volume control on a stereo:  it is a variable resistor; R1 is used to create a minimum resistance for the RC time constant, as VR1 can go down to zero resistance, so Ra limits this to a minimum value.

I would assume that you connect the coil under test, to a spark plug.  If it has no plug as a load, you will burn up the coil.  The HEI Module notes that its heat sink (metal outside casing, possibly with cooling fins, similar in appearance to the fins on the OEM Rectifier/Regulator's heatsink) must be connected to chassis ground/battery's negative terminal, or it may be damaged.

I would recommend finding someone trained in electronics to build it for you.  The components are not terribly expensive, but if you are not careful, you could destroy the HEI Module, which is expensive.  Cheers!