Measuring points on the VIC20 with an ocilloscope

[mrr19121970]

There is a nice article about the C64 here. Does anything like this exist for the VIC20?

6502 6510

I'll try to translate/interpret this.

This thread is not the entry point for error diagnosis, and the following assumptions are made:
1. You already checked if any ICs are too hot to touch
2. You checked your power supply, and it is working
3. You already tested all your socketed chips in a working board

For measurements in 8-bit computers with a frequency less than 10mhz, the following settings are recommended:

o Vertical 2v, so that 5v is visible over 2.5 squares. NMOS normally reaches 4v HIGH
o Horizontal 100ns, so that you have a resolution over about 5 squares for HIGH and LOW. You can see CLK-IN disturbances well.
o Triggering on the falling side in the middle of the screen. Here the CLK-IN cycle is on the left side and the VIC-I cycle on the right side.
o Using a 2 channel oscilloscope you can see the measurements in relation to the CLK-IN.

[mrr19121970]

1st we verify if a reset signal is obtained. This is on PIN40 of the 6502, and must be LOW/0V when turned off and HIGH/4-5V after a short time of turning on, and stay there. If this does not happen, then the possible culprits are UB6-LM555 and UB4-7406 and other components around the RESET logic.

Reset schematic here (top left)

Next check, does the VIC-I get the needed frequencies.Datasheet

Does the VIC-I get it's frequencies?

o Master Oscillator Clock PIN38 & PIN39 require 5v, non overlapping 4.437187mhz-PAL/14.31818mhz-NTSC (Clock-in phase-1 & 2)
o System Clocks PIN35 5v, non overlapping 1.02mhz clocks (Clock-out phase-1)

[eslapion]

The SAMS Computerfacts CC3 exists in 3 different version for the VIC-20.

Look here: https://www.c64-wiki.com/index.php/SAMS

There is a very large scanned sheet in there with a number of test points for values to look up on a multimeter and a number of waveforms to expect on an oscilloscope.

IMHO, Very useful.

Added edit: Ouch! I thought the PDF would be easy to grab and download... doesn't look like it!

[mrr19121970]

Good tip SAMS Computerfacts CC3 SAMS Computerfacts CC12

[eslapion]

@mrr19121970
Bingo!