1976 Chrysler 90hp 907HB Ignition Troubleshooting

[05blastsrt4]

1976 Chrysler 90hp 907HB W/magnapower ignition


Looking for a little insight here,

Trying to troubleshoot a no spark situation
As per the service manual I have 12-14 volts coming in on the blue wire coming into the preamp,
now out of the preamp while cranking I am varying anywhere from 1.5-6 volts coming out of the preamp.
I have no voltage coming out of the magnapower amplifier to the coil and obviously nothing coming out of the coil as well.
My question is what should the voltage be coming out of the preamp, trigger or whatever it is called?
And if the voltage is low could that be the cause of no voltage out of the main amplifier?

Thanks in advance....

 

[Frank Acampora]

Re: 1976 Chrysler 90hp 907HB Ignition Troubleshooting

On that engine there should be two blue wires: One to the electric eye and the other to the CD box. There should also be a power source from the battery through the red wire to the CD box. Red charges the capacitors and blue runs the internal electronics. Red is always hot, even with the key off.

The electric eye simply signals a gate transistor inside the CD box to dump the capacitors into the coil. Voltage is not 12 but quite frankly I have never measured it. However, if you are getting 1 volt with the eye blanked by the shutter and 6 with it open, that means it is probably working correctly.

 

[05blastsrt4]

Re: 1976 Chrysler 90hp 907HB Ignition Troubleshooting

On that engine there should be two blue wires: One to the electric eye and the other to the CD box. There should also be a power source from the battery through the red wire to the CD box. Red charges the capacitors and blue runs the internal electronics. Red is always hot, even with the key off.

The electric eye simply signals a gate transistor inside the CD box to dump the capacitors into the coil. Voltage is not 12 but quite frankly I have never measured it. However, if you are getting 1 volt with the eye blanked by the shutter and 6 with it open, that means it is probably working correctly.

I did some more research, and found some more testing procedures, using a dvm meter I attached the positive lead to the blue wire in the picture, and the negative, to the white wire with the black tracer. rotating the flywheel by hand I could see the voltage go from 12 to 0. Funny thing is while turning the flywheel I could hear the "snap" of spark. Put everything back together and it started right up.
I am not sure if it was something I did that fixed it or maybe my amplifier is on the way out.