How do you check the dist. module?

walt69

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With the DMM still connected to the negative side of the coil you are going to watch the meter while blocking the optics on the module with your credit card. Placing the credit card or other device between the towers on the module blocks the optics. When the optics are blocked the readings on your meter MUST drop below 2-volts.

Can someone explain this a little better? What do they mean by "blocking the optics"? Where are the optics? What are the "towers"?
Thanks
 

kev2

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year-make-model-eng-trans-color, problems and or symptons
 

walt69

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The module is in a Mallory 75 series Distributor. Not stock to vehicle. 69 Corvette 350/300, th400 trans. Engine started to die after running for several minutes. After a few minutes the eng. would start back up only to die again. after 3-4 times of doing this the engine would not start again. I have power to the distributor but no spark to the plugs. I jumped my battery with a battery charger prior to this happening so I believe I fried the module. Just not sure how to check the module.
kev2 said:
year-make-model-eng-trans-color, problems and or symptoms
 

NickD

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Obviously the negative side of the coil is connected to an NPN transistor that switches on when the light between and LED and photo detector is broken, less than 2 volts represents the saturation voltage of that transistor. Thought optical couplers were out, this must be an old unit, magnetics are far superior for pulsing the electronics to basically switch the coil on or off. Not really much of a test to just check forward saturation voltage, the rise and fall times of the pass transistor are extremely important to generate a spark of any appreciable voltage, normally less than 0.25 microseconds.

Has to be a light interrupted between those towers and for a V-8, should have eight fins.
 

PC

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Could probably crank the motor with the voltmeter connected to the negative side of coil and see if there is voltage change as it cranks. Same as opening and closing the points. Drop the original dist. in and see if it fires up. Possible the coil gave up the ghost.
 

NickD

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Insulated gate bipolar transistors are most commonly used today to switch the primary of the ignition coil with barely enough circuitry just to replace the points. Unlike an old fashion type bipolar transistor that requires a huge base drive current these devices have an extremely high input impedance so no preamplification is required. Cheap, don't know if you have a PC board or a thick film circuit, the former can be repaired or even modified for improved performance.

When aftermarket solid state ignition modules first came out in the 60's, sure they replaced the points, but the fall times were so poor, would barely get a spark where when a set of points were opened, the fall times were practically instantaneous for a very hot spark. The rate of which the module switches off determines how much voltage is induced in the secondary and makes the difference between getting either 6,000 or 40,000 volts.
 

Mobile Dan

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With today's advances in medicine, bipolar transistors no longer need insulated gates. Proper treatment and medication can allow them to live freely among "normal" transistors and even contribute to society.
 

NickD

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I got more life out of my 70 Buick Rivera back then by installing an intake manifold from a 73 455 with an EGR hole in it, that along with a set of Canadian thicker head gaskets to reduce the CR to a more reasonable 8.5:1 let me burn unleaded gas with burning up the valves. Also installed an HEI distributor and a 10SI alternator to get rid of those troublesome points in either the distributor or the voltage regulator. Had a good friend at Delco, he was going to charge me 13 bucks for both the distributor and the alternator, his cost, but said it wasn't worth invoicing. The manifold was from a 73 when I still could go to my wrecking yard before the state passed all these liability laws. Walked in the yard with a pair of pliers and a screwdriver in my back pocket and removed them myself for a couple of bucks.

Today, you have to buy the entire engine at about the same price as the new one.

Main reason for the change was getting impossible to buy leaded premium gas, and the lead content was reduced to about 10% of the original value, had my share of detonation problems plus unleaded was selling for 75 cents a gallon where the leaded premium was more like a buck sixty a gallon. Amazingly, the car ran just as fast with about the same fuel economy, so why the high compression? But that car only lasted a couple of more years, road salt got to it.
 
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