Power Transistor

Ignition Coil And Power Transistor Circuit:

To test the Power Transistor / Ignition Coil, located in the distributor, use an analog type circuit tester and proceed as follows:

Component Test:

POWER TRANSISTOR
1. Disconnect the power transistor / ignition coil connector.
2. Connect a power supply of 1.5v (one dry cell) between power transistor terminals 2 (-) and 1 (+).
3. Check for continuity between terminals 2 (+) and 3 (-).

Continuity
Should exist

4. Remove power from terminals 1 and 2.
5. Check for continuity between terminals 2 (+) and 3 (-).

Continuity
Should not exist

IGNITION COIL
1. Using an ohmmeter, check the resistance value between terminals 1 and 2.

Resistance value
0.77 - 0.88 ohms

2. Using an ohmmeter, check the resistance value between terminals 2 and high tension terminal.

Resistance value
11k - 13k ohms

If the Power Transistor / Ignition coil module fails any of these tests, replace as a module.

Primary Ignition Coil Signal Pattern:

OSCILLOSCOPE TEST
1. Run engine at idle speed.
2. Connect the scope probe to pick-up point #1 shown in the system schematic diagram and compare the primary ignition coil signal to the pattern shown.

Power Transistor Control Signal Pattern:

3. Run engine at idle speed.
4. Connect the scope probe to pick-up point #2 shown in the system schematic diagram and compare the power transistor control signal to the pattern shown.
If scope patterns are not as depicted in images, continue with the rest of the test procedures before replacing the assembly.

For additional testing procedures, refer to COMPUTERIZED ENGINE CONTROLS.