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Help With Schematic Diagram

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BaronJ:
Hi Andrew,  I 100% agree.

A couple of years ago I was asked if I could repair some Mercedes ECU/EMC boxes. Real swine to get into them, with pressed steel plate box construction with a roll sealed steel lid.  It took an age just to get the lid off.  Problem was that even after you got in there, the PCB was coated with a thick transparent epoxy.  Horrible thing !  You could measure a very low resistance across the power rails on the socket pins, you could even see the burnt shorted device through the coating.  I eventually rejected the units and gave them back.  At the time I think the cost of an exchange one was in the £1200 + region.  Heaven knows what they did with them when they went back.

AdeV:
As others have mentioned, the diodes are generally known as "snubber" diodes, and they're used to prevent a spike of reverse-polarity power from being put onto the power rails by any kind of inductive load (typically, a relay coil, or motor winding). The reversed spike can cause significant damage to electronics, such as microcontrollers or the MOSFETs which are often used to switch things on & off under MCU control.

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