Electronics > Beginners

Troubleshooting Microprocessors

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techman-001:

--- Quote from: bostonman on December 30, 2019, 12:32:54 am ---See the two pictures I included for a better idea of what I mean.

--- End quote ---

I have a 54601A scope myself, bought it new in 1994, use it every day and just love it  :-+

Picture is via the RS232 module and some Unix processing.

NivagSwerdna:
might be educational

bostonman:
I've kind of run out of ideas and feel maybe I should readdress repairing this in the future as I feel my measurements take me in a loop.

At the moment, any chips I suspect are not in sockets; nor do I have extras to swap (or my other C64 doesn't have those chips in sockets either).

Any chip I suspect is driven by the address bus which goes to several chips. Any other chip that has bad signals is either being told to be bad by the address bus or is the culprit.

Ideally I'd like the ability to freeze the unit so I can measure chips individually (which is how I opened my initial question), however, doesn't seem easy to do.

Per my initial question, trying to measure microprocessors comes down to needing a custom micro to freeze the bus and measure signals?

atmfjstc:
You don't need a "custom micro". As others have said before, the best tool for this situation is a logic analyzer. However, you can do without it (as the guy in the video did). A 4-channel scope, even a 2-channel scope could provide enough information to figure out what's going on. It'll just take more work.

I don't mean to sound mean, but I think your real problem here has nothing to do with the tools available. Looking at your posts, I'm not convinced you have done the research and truly understand how the C64 works and what signals to expect. I'm not even sure you understand how buses work. A tool, however advanced, can only make your work easier and faster, but can't do the thinking for you.

Sometimes you can get lucky and stumble your way into a solution without really understanding what's going on. But just as often, you will hit a brick wall.

If I were you, I'd spend a few days researching the 6510, VIC, the RAM/ROM chips, the C64 schematic, what all the pins mean, and how the chips work together. I think you'll find that none of the chips' behavior is really that complicated. And then you'll know exactly what to look for and how to recognize incorrect behavior.

bostonman:

--- Quote ---I don't mean to sound mean, but I think your real problem here has nothing to do with the tools available. Looking at your posts, I'm not convinced you have done the research and truly understand how the C64 works and what signals to expect.
--- End quote ---

You're not completely wrong. Generally speaking, I know what a ROM does, RAM, etc... and been around electronics long enough to know about signals. On paper, it's much easier to interpret the signals because a datasheet states which pins need to be high/low to process data.

I do, however, get overwhelmed by the many signals and where to look in order to find the origin of the signal(s). You're correct, maybe I should sit and read the many pieces of information in order to understand the C64 better. When it comes to the microprocessor section of any piece of electronics I've worked on, I always get overwhelmed. I'm also a bit timid because this is my original C64 and not some random piece I bought. So I don't want to hack the board and trying to approach the problem methodically.

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