IBM 4232-302 -- Cover Interlocks

There are two cover interlocks, one for the top access cover and one for the front door. They're both Hall-effect sensors 'actuated' by permanent magnets.

The top access cover's magnet is situated where it can act on a sensor that's inside the rear left corner of the control panel. The front door sensor's magnet is inside at the upper left of the front door.

Neither cover being open disables the printer. Instead, the printer remains operational while displaying the message, "090 COVER/DOOR OPEN PRINT SPEED REDUCED". Hence, it's not essential to cheat the interlocks in order to investigate machine operation with the cover removed. However, there is a way to do it should the need arise.

To cheat the front door interlock, unplug the sensor's connector and short the lower contact to chassis ground, like so.

(The "DC" on the connector stands for "Door Closed".) Be certain that you have the correct contact, the lower contact, pin 1. The centre contact is ground. The upper contact is the sensor's V_CC supply (+5 VDC) -- shorting that one to ground might cause damage to the Logic PCA.

To cheat the sensor in the control panel, first free its cable so you can lay the control panel on a nearby work surface. Place a suitable magnet against the rear left corner of the control panel to 'actuate' the sensor. Pictured below is a magnet from a cabinet door latch being used.

The sensor is sensitive to magnetic polarity, so you have to experiment a bit to find the magnet orientation that works.

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