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A PCB that I designed just came in (schematic pictured below). After soldering the components in, some things are happening that I don't understand. Most importantly, one part of the circuitry, an H-Bridge is used, however, at JP2 pin one has a voltage of .8v rather then 12v that the circuit is powered with. This behaviour is observed when Q1, Q3 and Q6 are "actuated" (or set HIGH) by the attiny85.

I've tried to google this, but have had no luck, as I have no idea of how to describe it using keywords, because I don’t really know what the problem is or how it has been caused.

My question is: Why is this happening? And how do I stop/fix this? enter image description here

user2503170
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That is a terrible schematic. See this description of how to draw a proper schematic.

In any case, your primary problem is that you don't seem to understand that when it is conducting, the emitter voltage of an NPN transistor can never be higher than its base voltage. In fact, it will be lower by at least 0.65 V. You're driving the base of Q1 with a logic signal from a 5-V MCU, so its emitter will be no more than about 4.3 V, probably less. Same thing with Q3 and Q5.

Also, I can't figure out what S2 is supposed to be doing. Are you sure you have a current path to the collector of Q1?

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Dave Tweed
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    Also, since the bases of Q3 and A6 are connected, and likewise Q4 and Q5, emitters of Q3 and Q5 will be about the same voltage as the emitters of Q4 and Q6 - therefore no voltage across the bridge. – Peter Bennett Jul 13 '15 at 20:56