So I did a slight bit of testing on the Commodore 64 I picked up. When I power it on, the TV gets a signal, but the screen is black. This can be caused by one of three things, the CPU, the PLA (Programmable Logic Array) or the VIC II video chip.
I took my multi meter to the board to
make sure I was getting the correct power throughout the board,
everything checked out, I seemed to be getting power to all the places
power needed to go. I put my dead test cartridge in and still got a
black screen. The cart will usually run even if the memory is bad or
the VIC II is not working. This kind of narrows it down to the PLA or
the CPU, of the two, the PLA is far the most likely to go bad than the
CPU. Fortunately there are some cheap replacements out there for around
$20 so I have ordered one. In the meantime, there is a key missing, so
my plan this weekend is to repair the keyboard, I already have
everything I need for that.
In this picture, I have pulled the PLA.
Looking at it, I probably need to clean the board as well.
Edit: The events described in this post occurred Wednesday Oct 9th 2019.