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I am REALLY new at this. Fixing a Z-80 firmware program.

I am getting my feet wet with this, here is my issue:

I am working with a Z-80 based embedded control system in a machine, specifically a hot stamp printing press.

Specifically I am trying to learn exactly what conditions cause a given situation to happen. I have two machines, they are very similar, one (the older one) works pretty well. The other (the new and improved one) has been problematic since it was new.

I have burned an EPROM to match the older one and installed it in the newer machine. Now the newer machine works a lot better. But I still have the same error happening.

Something in the firmware is causing a mechanical component to act bad, by keeping it turned on when it should be off. But the machine will just keep on plugging along.

Conversely, if this component develops a mechanical problem, somehow this condition is spotted and the machine shuts down with an error message (this error message is also located in the EPROM).

The manufacturer of the machine is absolutely no help, they no longer produce this type of machine at all. There is very sketchy documentation available.

So essentially, I need to reverse engineer the firmware to determine where the problem lies in the machine. I am learning a lot quickly.

I have strings of hex codes. I can convert it into assembly mnemonics. But I'm trying to learn exactly what they mean. I'm not trying to re-create the world or steal someone's ideas, just to understand exactly what is going on, so I can intelligently determine what is wrong - and even correct errors and make it better.
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