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kynikos

C64 SID diagnostics confusion

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Hi all, I recently picked up my first C64 and am a bit confused after running some diagnostic tests. On both the 586220 and 586220* diagnostics my 6518 U18 is showing as "bad", which I understand is the SID chip. However, when running the SID Tester by Andrew Challis, everything passes and I can hear all the sounds fine. Games sound fine as well. Should I be concerned that my SID dying or would this just be a diagnostic test discrepancy? Thanks in advance!

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The question is what the test is really testing. Since the machine can’t hear the SID it can only look at the input it has - paddles and the waveform/envelope output registers. So either paddles aren’t working or reading the waveform output isn’t working properly. Try paddles on it or a program that auto detects the SID type. Either of those might be failing.

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Hi all, I recently picked up my first C64 and am a bit confused after running some diagnostic tests. On both the 586220 and 586220* diagnostics my 6518 U18 is showing as "bad", which I understand is the SID chip. However, when running the SID Tester by Andrew Challis, everything passes and I can hear all the sounds fine. Games sound fine as well. Should I be concerned that my SID dying or would this just be a diagnostic test discrepancy? Thanks in advance!
The SID is used for reading analog joysticks and the 586220 is testing that functionality as part of the control port test. It reports bad SID if the analog parts of the control port tests fail.
You need a test harness that connects to the control ports and other ports to run the 586220 and get all good results.
Is the bad U18 indication showing up right after the control port test has finished?

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54 minutes ago, hofster said:

The SID is used for reading analog joysticks and the 586220 is testing that functionality as part of the control port test. It reports bad SID if the analog parts of the control port tests fail.
You need a test harness that connects to the control ports and other ports to run the 586220 and get all good results.
Is the bad U18 indication showing up right after the control port test has finished?

It basically looked like the attached image. I had nothing else plugged in so that might explain it. I'm not sure I want to spend the money on a test harness right now as this is my only C64 and I don't really plan on getting more.

diag4.png

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