Servicing the Gottlieb System 1 pinball game

Posted on Feb 7, 2014

A cure that we are testing is to prevent the over voltage getting to the irreplaceable IC U5 - A1752CF after either the switch drives or returns are hit with either a static electric shock or the 24VDC solenoid bus. The protection is simple, there needs to be clamping diodes inserted in the circuit. These can be placed across the resistors R65 - R

Servicing the Gottlieb System 1 pinball game
Click here to download the full size of the above Circuit.

72 with the band of the diode (1N4002 or higher) soldered to the +5VDC end of the resistor and the non-band end to the other side of the resistor. Then on Resistors R57 - R62, connect the non-banded end of the diodes (1N4002. ) to the junction of the resistor and the trace leading to the IC and the banded end to a convenient +5VDC bus tie point. The (-12VDC) is the negative bus rail, and the (+5VDC) is the +5 bus rail. The -|>|- is a diode. The (input/output) is EITHER the input or output line to be protected. This will prevent the input/output lines from going above the +5VDC line and thus protect the IC`s from the 24VDC solenoid bus or the 6. 3VAC light bus power. The earlier run of Gottlieb driver boards did not isolate the MPU board from the solenoid driver transistors, and if a coil shorted out, this can cause serious damage to the MPU board. Essentially making it very expensive to service! Please check the picture on the lower left (here is a circuit diagram with the diodes) and see if you have these on your board. The early boards can be updated by inserting diodes directly at the base of the driver transistors (picture #2), or traces were cut on the back and the diodes soldered in (picture #3). The recommended diodes would be 1N4002 to 1N4005 series, Do not use a 1N4001, at 50V it is not rated with a high enough breakdown voltage. We recommend that ALL Gottlieb System 1 game owners confirm this modification has been...

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