The heart of the Commodore 16 is the CPU. This comes in the form of a MOS 8501. It is a modified 6510 CPU with a 7 bit data port, and a 7 pin I/O port (used for Tape/Serial I/O).

Faults

Below are some common faults with the CPU.

Running Too Hot

This commonly runs too hot and dies often. An external heat sink is highly recommended.

Black Screen

A dead CPU usually results in black screen, and if using a diagnostics ROM also results in black screen (as the ROM needs the CPU to run its code).

Oscilloscope Diagnostics

The simplest way to test for a dead CPU is to use an oscilloscope and probe all the pins. Often a dead CPU will have its CMOS gates floating between a logic level (so somewhere between 2V and 4V is typical for a bad gate.

Here is an example of a bad A13 pin.

And here is what it should look like:

Notice the full pull to ground on the pulses, and rising to anywhere from 3V to 5V depending on cycle.

Working Examples

Some example scopes of working pins for reference that commonly die on the CPU.