Since the blog section is more or less dead and goes unnoticed, I'll tag a few people who already knew from PM I was messing with this (without now further telling in the public why I'm doing this)
Feel free to ignore, but just in case you want to see it: @Alexander1970, @Blauhasenpopo, @Sono, @VinsCool
Still being at the very beginning in the process of understanding at least the slightest part of the basics in optical discs/drives (hard to find good information online – going deep and being generally understandable), I wanted to find out what happens when manually applying very small voltage to the coils responsible for moving the lens left/right. Would I be able to simulate what the “auto-correcting” circuity does when following the track by evaluating if all photodiodes roughly measure the same intensity of reflection? (Details for this go way above my head). Means: No, I've no idea what I'm doing here.
I just wanted to move the lens and get an idea what amount of voltage and amperage (→ energy) is needed. In what order of magnitude is this?
Gently tapping the lens in an optical pickup with a soft plastic tool makes it move sooo much left/right and up/down! It is hard to touch it so little that it does not move all the way to one side. The “floating” lens weighs next to nothing and has to be able to react to tracking and focus errors at INSANE ~s p e e d~. These little previous knowledge tells us: Start with the absolute minimum of energy!
Fearless Testing Sina opened a useless, old CD-ROM drive (IDE based, so nothing special or really old and maybe worth preserving).
Here is the optical pickup head with four distinct points. Two for focus and two for tracking. The latter is my target.
I couldn’t solder there. Well, maybe I could, but the wires would be in the way afterwards. Luckily a ribbon cable goes right to the motherboard where I could solder on some wires with my shaking hands on the connector (forgot to drink a bit of booze to lessen the tremor). Not pretty, looks shorted, but it isn’t. The red and black wires are connected to the two points for tracking.
My brave helper took a video (after having begged them enough to take the risk and providing some gloves) to show the result. Unfortunately the cheap lab power supply doesn’t go below roughly 0.1V – it goes straight to 0.0V when turning down further and the fine tuning doesn’t do sh*t in the low voltage area. Luckily 0.1V is in the correct order of magnitude! Yes! The lens moves gently to the left/right depending on polarity. Don’t get irritated by the display of the lab power supply. It shows just zero for the voltage, but the multimeter is more precise.
First a complete picture showing the problem with the wrong zero volt on the power supply.
Then the very short video. Note that is is not easy to spot the lens movement on a small screen. But it is there and very noticeable on big screens, so use a proper PC monitor instead of a puny phone to watch this if you want to actually see something.Maybe I can get an additional video later on showing only the lens and not the wires. Not possible anymore. The optical pickup got fried trying to record data with a sound card. This disturbs the tracking system so much, that it becomes inoperable. I tried a few times too often and ultimately it failed completely.
However, I was able to measure AC voltage during normal operation with the multimeter (like expected). The fast the drive was reading, the higher the voltage (up to about 0.25V AC).
I will try to repeat this with another drive someday.
As there was no needed audio information, I removed the audio stream to save bandwidth/data.
Next step: Reassemble and test if the drive is still operable. My theory is that one could visualize the optical pickup following the track (as well as following certain tracking errors) by connecting an oscilloscope – which I sadly don’t have. This should be possible for the case that connecting anything to that insanely sensitive circuity doesn’t disturb normal operation.
Feel free to ignore, but just in case you want to see it: @Alexander1970, @Blauhasenpopo, @Sono, @VinsCool
Still being at the very beginning in the process of understanding at least the slightest part of the basics in optical discs/drives (hard to find good information online – going deep and being generally understandable), I wanted to find out what happens when manually applying very small voltage to the coils responsible for moving the lens left/right. Would I be able to simulate what the “auto-correcting” circuity does when following the track by evaluating if all photodiodes roughly measure the same intensity of reflection? (Details for this go way above my head). Means: No, I've no idea what I'm doing here.
I just wanted to move the lens and get an idea what amount of voltage and amperage (→ energy) is needed. In what order of magnitude is this?
Gently tapping the lens in an optical pickup with a soft plastic tool makes it move sooo much left/right and up/down! It is hard to touch it so little that it does not move all the way to one side. The “floating” lens weighs next to nothing and has to be able to react to tracking and focus errors at INSANE ~s p e e d~. These little previous knowledge tells us: Start with the absolute minimum of energy!
Fearless Testing Sina opened a useless, old CD-ROM drive (IDE based, so nothing special or really old and maybe worth preserving).
…until I found one with an internal design suitable for my stupid idea.
I couldn’t solder there. Well, maybe I could, but the wires would be in the way afterwards. Luckily a ribbon cable goes right to the motherboard where I could solder on some wires with my shaking hands on the connector (forgot to drink a bit of booze to lessen the tremor). Not pretty, looks shorted, but it isn’t. The red and black wires are connected to the two points for tracking.
My brave helper took a video (after having begged them enough to take the risk and providing some gloves) to show the result. Unfortunately the cheap lab power supply doesn’t go below roughly 0.1V – it goes straight to 0.0V when turning down further and the fine tuning doesn’t do sh*t in the low voltage area. Luckily 0.1V is in the correct order of magnitude! Yes! The lens moves gently to the left/right depending on polarity. Don’t get irritated by the display of the lab power supply. It shows just zero for the voltage, but the multimeter is more precise.
First a complete picture showing the problem with the wrong zero volt on the power supply.
Then the very short video. Note that is is not easy to spot the lens movement on a small screen. But it is there and very noticeable on big screens, so use a proper PC monitor instead of a puny phone to watch this if you want to actually see something.
However, I was able to measure AC voltage during normal operation with the multimeter (like expected). The fast the drive was reading, the higher the voltage (up to about 0.25V AC).
I will try to repeat this with another drive someday.
As there was no needed audio information, I removed the audio stream to save bandwidth/data.
Next step: Reassemble and test if the drive is still operable. My theory is that one could visualize the optical pickup following the track (as well as following certain tracking errors) by connecting an oscilloscope – which I sadly don’t have. This should be possible for the case that connecting anything to that insanely sensitive circuity doesn’t disturb normal operation.
