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Challenge: Debug my SPDIF waveform
Challenge: Debug my SPDIF waveform
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Old 18th August 2017, 07:49 PM   #1
peufeu is offline peufeu  France
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Default Challenge: Debug my SPDIF waveform

While sorting through my huge RAID array, I came upon this old video, so I must share it with you now. This is a scope shot of the SPDIF output of a CD723.

Zippyshare.com - spdif_jitter.avi

Now, I'd like you to look at the video, please forget the terrible rising edge in the foreground, and focus on the other traces crossing in the background, which are other parts of the SPDIF signal.

Play the video. Notice how the traces wiggle and move around, as if the signal were a little bit drunk. Now, this is digital silence, none of that quirky audio sample data, just zeros, so it should be pretty steady on screen. But the jitter is visible to the naked eye, and you don't even have to squint.

CHALLENGE: Find what caused this.

Winner gets bragging rights.
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Old 19th August 2017, 06:59 AM   #2
percival007 is offline percival007  England
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You, just touching the Cable?

;-)
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Old 19th August 2017, 10:45 AM   #3
peufeu is offline peufeu  France
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That would be too easy There was no cheating involved...
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Old 19th August 2017, 12:29 PM   #4
Ken Newton is offline Ken Newton  United States
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Perhaps, some low frequency wander due to a defective power supply/regulators?
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Old 19th August 2017, 02:04 PM   #5
peufeu is offline peufeu  France
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Congrats, you are on the right track! The power supply is involved, although nothing is defective: it is that bad out of the box. But what kind of load inside a CDP can cause this?
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Old 20th August 2017, 12:45 AM   #6
wwenze is offline wwenze  Singapore
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It is always motors that make the most noise... unless the root cause is funny this time.
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Old 20th August 2017, 08:11 AM   #7
peufeu is offline peufeu  France
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It is due to a mechanical actuator, but not the main motor. Hint: I was walking in the room when this happened.
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Old 20th August 2017, 08:51 AM   #8
audio_tony is offline audio_tony  United Kingdom
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It would have to be the sled motor or laser focus then.

Any mechanical disturbance would cause the laser to lose it's tracking requiring sudden changes to focus and possibly even laser position.

The above actions would place sudden short term current demands on the PSU.
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Old 20th August 2017, 09:29 AM   #9
peufeu is offline peufeu  France
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Exactly.

Vibrations in the room cause the spinning disc to move and have to be compensated by the actuators which draw current. Voltage on the power supply reflected this. And the PSU design was bad enough that every supply inside the box (digital, analog, etc) had vibration-dependent ripple on it. Enough to affect output jitter (and not subtly).
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Old 20th August 2017, 11:15 AM   #10
percival007 is offline percival007  England
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What Make of Player was it?
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