Commodore 16
According to the wiki page, the Commodore 16 is a home computer made by Commodore International with a 6502-compatible 7501 or 8501 CPU, released in 1984 and intended to be an entry-level computer to replace the VIC-20. A cost-reduced version, the Commodore 116, was mostly sold in Europe.
Unlike the Commodore 64 it has a combined sound and graphics chip the so-called TED. This chip is prone to failure and most machines you'll find on eBay or other auction sites, have a high likelihood of a failed TED. Paulo Garcia is working on a TED FPGA replacement, but it's still a work in progress, link.
Just like with the C64 and other Commodore models the PLA chips are also prone to failure, the C16 is no exception. However, Daniël Mantione, has created a GAL version, the PLA16v8, just like the one for the C64, to replace the PLA in the C16. The GAL16v8 chips he used are very easy to obtain and the price point is fantastic. He sells complete kits or you order the boards from him.
I've also encountered numerous C16s with faulty CPUs. The 8500 series CPU is basically a 6510, but produced using a different manufacturing process. This process was cheaper, but the effect is that a lot of the 8500 CPUs will fail. A small adapter can be ordered from PCBway to use a more common 6510 CPU in a C16.
On the left you see a wire to add A14 and A15 address lines to the CPU from the 74LS257 to enable the 64kB
I started with a black screen, but the PAL signal comming out of the machine was correct, just black. That gave me hope about the TED. I used a C16 Diagnostics rom image burned on a 27512 eeprom that fits directly in place of the Kernal rom on the board.
Switching the machine on gave me an image. The CPU was doing something and the TED was providing an image. That gave me even more hope.
As if the list of part to fail in a C16 wasn't long enough. The memory (2x4416) is also prone to failure. So I immediately decided to use two 4464 chips and upgrade to 64kB. With this upgrade you can run Plus4 software as well, increasing the software library for this machine.
