There's no excuse for the ridiculous way the shop went about "diagnosing" the charging system issue. It sounds like they didn't know what they were doing...plain and simple. And "waiting on some diodes" is pretty weak also...considering the allegedly bad diodes were found after throwing other parts at it first.
I don't know what the ultimate outcome of this situation will be, but in the future I do have a suggestion. (This kind of thing occurs where I work as well, so I feel your pain.)
When you take something in for any type of repair, it should be accompanied by a document you created in advance. If your machine has issues, list the issues you want addressed specifically. In this situation, I would have described the charging system issue as best I could, as well as any steps taken on my own to try and fix it.
When the machine is dropped off, give a copy of your document to the service writer or supervisor, and ask them to make a copy for you to take with you when you go. This may raise some eyebrows, but it will show them that both parties involved are working from the same set of instructions. What (unfortunately) happens in lots of shops, is that there's a chain of command. You tell a service writer what you need done. Sometimes he'll enter the information into his computer verbatim as you say it, while other times he'll scribble notes and enter it later. Then, he'll relay the information to the tech doing the work by providing them a printed copy of the work order, OR....he'll "tell" them what needs to be done. Telling the tech often means he'll "interpret" what you've said and put it into his own words. Once the tech gets the information, then his "interpreting" begins.
In a typical shop, there are about 3 or 4 steps along the way for misinterpretation, poor communication, and other such nonsense to take place. Add to that the fact that nowadays it's becoming de rigueur for people to use communication techniques like "texting shorthand", and the possibilities for mistakes multiply. I end up calling customers a lot to see exactly what they wanted to have done, because the details I receive are unclear and/or incomplete. I would love it if every item that came in was accompanied by a document from the owner.
I would also love it if companies doing the hiring would put more emphasis on communication skills, and stress that poor communication wouldn't be tolerated. If the people at the shop we're discussing here possessed good communication skills, then that ability to speak, read, and write would likely carry over to other things as well....such as the ability to sit down down and read a schematic instead of just swapping parts at random.

I don't know what the ultimate outcome of this situation will be, but in the future I do have a suggestion. (This kind of thing occurs where I work as well, so I feel your pain.)
When you take something in for any type of repair, it should be accompanied by a document you created in advance. If your machine has issues, list the issues you want addressed specifically. In this situation, I would have described the charging system issue as best I could, as well as any steps taken on my own to try and fix it.
When the machine is dropped off, give a copy of your document to the service writer or supervisor, and ask them to make a copy for you to take with you when you go. This may raise some eyebrows, but it will show them that both parties involved are working from the same set of instructions. What (unfortunately) happens in lots of shops, is that there's a chain of command. You tell a service writer what you need done. Sometimes he'll enter the information into his computer verbatim as you say it, while other times he'll scribble notes and enter it later. Then, he'll relay the information to the tech doing the work by providing them a printed copy of the work order, OR....he'll "tell" them what needs to be done. Telling the tech often means he'll "interpret" what you've said and put it into his own words. Once the tech gets the information, then his "interpreting" begins.
In a typical shop, there are about 3 or 4 steps along the way for misinterpretation, poor communication, and other such nonsense to take place. Add to that the fact that nowadays it's becoming de rigueur for people to use communication techniques like "texting shorthand", and the possibilities for mistakes multiply. I end up calling customers a lot to see exactly what they wanted to have done, because the details I receive are unclear and/or incomplete. I would love it if every item that came in was accompanied by a document from the owner.
I would also love it if companies doing the hiring would put more emphasis on communication skills, and stress that poor communication wouldn't be tolerated. If the people at the shop we're discussing here possessed good communication skills, then that ability to speak, read, and write would likely carry over to other things as well....such as the ability to sit down down and read a schematic instead of just swapping parts at random.