WEBVTT Kind: captions Language: en 00:00:00.080 --> 00:00:04.280 This exploded machine is capable of a marvelous feat. 00:00:04.280 --> 00:00:09.500 These parts, when assembled correctly, are able to interact with this silver plastic thing 00:00:09.500 --> 00:00:13.580 and make melodious sounds for you to enjoy in the highest of fidelities. 00:00:14.500 --> 00:00:15.820 Am I being vague? 00:00:15.830 --> 00:00:16.830 Maybe. 00:00:16.830 --> 00:00:19.779 Well, more specifically, this is a compact disc player! 00:00:19.779 --> 00:00:25.100 The innards of a Magnavox CDB 260, made in August of 1988. 00:00:25.100 --> 00:00:28.790 From what I can gather this is a pretty basic CD player, even for the time. 00:00:28.790 --> 00:00:31.010 But that’s fine, in fact it might even be better. 00:00:31.010 --> 00:00:32.300 So, in the last video, 00:00:32.300 --> 00:00:32.800 *ding* 00:00:32.800 --> 00:00:36.200 we talked about how the data is stored on a compact disc. 00:00:36.210 --> 00:00:40.920 Just below the top surface of the disc, millions of little bumps are found in the polycarbonate, 00:00:40.920 --> 00:00:46.050 and the aluminum coating will reflect light like a mirror back from whence it came. 00:00:46.050 --> 00:00:51.480 These bumps, from the bottom side, form pits and lands and they are what encodes the data. 00:00:51.480 --> 00:00:55.920 So the first thing any CD player will need to do is to shine a light on the CD, a light 00:00:55.920 --> 00:01:01.719 so finely focused that it’s shining mostly on only one track, and it needs a way to detect 00:01:01.719 --> 00:01:04.170 the change in brightness caused by the pits. 00:01:04.170 --> 00:01:06.259 That’s what this guy does, here. 00:01:06.259 --> 00:01:08.939 This is the laser and lens assembly. 00:01:08.939 --> 00:01:12.689 To understand what it does, it’s best to take a look at it from this angle. 00:01:12.689 --> 00:01:13.689 Excellent. 00:01:13.689 --> 00:01:17.869 OK, so notice that there are two circuit boards at right angles to each other. 00:01:17.869 --> 00:01:21.319 This one to the side is where you will find the laser diode. 00:01:21.319 --> 00:01:24.359 This is what creates the beam of light that will read the disc. 00:01:24.359 --> 00:01:28.880 The light from the laser diode gets shot straight to the left, and a prism, right about here, 00:01:28.880 --> 00:01:32.780 will cause the light to make a 90 degree turn, and end up going... 00:01:32.780 --> 00:01:34.189 up through the lens, and 00:01:34.189 --> 00:01:35.689 onto the disc. 00:01:35.689 --> 00:01:39.749 Because the disc has a mirrored surface, that light is gonna come straight back down through 00:01:39.749 --> 00:01:40.899 the lens. 00:01:40.899 --> 00:01:43.469 And here’s where the other circuit board comes in. 00:01:43.469 --> 00:01:46.959 Some of the light being reflected from the CD will go straight through the prism and 00:01:46.960 --> 00:01:48.320 end up at the bottom. 00:01:48.320 --> 00:01:52.319 Now you can’t see them because this is sealed and I don’t really want to break it but 00:01:52.319 --> 00:01:57.939 inside, on top of the circuit board, there are 4 photodiodes arranged in a 2 x 2 grid. 00:01:57.939 --> 00:01:59.749 Why are there 4, you ask? 00:01:59.749 --> 00:02:03.789 Well, not only do the photodiodes need to react to the changes in brightness of the 00:02:03.789 --> 00:02:08.479 reflected light in order to, for lack of a better word, detect the zeros and ones, but 00:02:08.480 --> 00:02:11.420 they also forms the basis of the focus and tracking system. 00:02:11.760 --> 00:02:12.460 A ha! 00:02:12.470 --> 00:02:13.969 A new thing to unpack. 00:02:13.969 --> 00:02:15.829 No CD is perfect. 00:02:15.829 --> 00:02:20.390 All of them are going to have some deviations from perfectly flat, and they’re also probably 00:02:20.390 --> 00:02:25.120 not going to be held exactly perfectly centered, so the track of pits will waver like this 00:02:25.120 --> 00:02:26.420 off-center record. 00:02:26.420 --> 00:02:30.890 To stay on the same track of pits and lands, some mechanism will need to be able to move 00:02:30.890 --> 00:02:36.049 the lens closer to and farther away from the disc, in other words stay focused on it, and 00:02:36.049 --> 00:02:40.730 there will also need to be a way to move the lens back and forth as the spiral track wobbles. 00:02:40.730 --> 00:02:42.689 In other words, it needs to track it. 00:02:42.689 --> 00:02:46.440 Philips’ solution to the problem of focus and tracking is the less common one, but it 00:02:46.440 --> 00:02:49.530 is so much more elegant than Sony’s in my opinion. 00:02:49.530 --> 00:02:53.260 I’ll show you Sony’s system later on, but if you didn’t see my last video, I showed 00:02:53.260 --> 00:02:56.940 you the disc tray of this machine and suggested it hinted at the difference. 00:02:56.940 --> 00:02:58.939 So, first the easy bit. 00:02:58.939 --> 00:03:03.480 To maintain focus on the disc, the lens is floating, and you can kinda see that there’s 00:03:03.480 --> 00:03:06.520 a coil of wire that can push it up or pull it down, 00:03:06.520 --> 00:03:09.379 pretty much exactly like a loudspeaker driver. 00:03:09.379 --> 00:03:13.680 The low mass of the lens allows it to react practically instantly to changes in the distance 00:03:13.680 --> 00:03:18.980 between the CD and the lens, so even a badly warped CD won’t fool the CD player. 00:03:19.320 --> 00:03:21.280 Alright, we have the Y axis accounted for. 00:03:21.290 --> 00:03:25.420 But how do we move the lens left and right, in order to account for a wibbly wobbly track? 00:03:25.420 --> 00:03:29.609 Well, notice that the lens is on an arm that’s surrounding a metal disc. 00:03:29.609 --> 00:03:33.299 This allows the lens to rotate around the disc, and you’ll notice that this disc is 00:03:33.299 --> 00:03:34.749 a magnet. 00:03:34.749 --> 00:03:39.019 Flip this upside down and you'll find another coil of wire, surrounding the magnet. 00:03:39.019 --> 00:03:43.590 This swing-arm design is remarkably similar to how hard drives move their read/write heads 00:03:43.590 --> 00:03:49.239 with a voice coil, and it’s this that sets the Philips design far apart from Sony’s. 00:03:49.239 --> 00:03:53.650 Because the lens can move vertically, and its platform can move horizontally, constant 00:03:53.650 --> 00:03:55.870 focus and tracking can be maintained. 00:03:55.870 --> 00:03:59.810 Now, I’ll reattach the laser mechanism to the spindle motor assembly. 00:03:59.810 --> 00:04:03.810 It has ball bearings on the top and bottom, and when this bracket is in place the arm 00:04:03.810 --> 00:04:07.099 essentially floats and moves nearly effortlessly. 00:04:07.099 --> 00:04:11.779 This mechanism is fastened to this assembly, which also operates the disc tray. 00:04:11.779 --> 00:04:15.420 The disc tray is made in two pieces, and it’s a rather unique design. 00:04:15.420 --> 00:04:19.810 The bottom half sort of drops down when it is inserted into the player, and you can sort 00:04:19.810 --> 00:04:21.780 of move it even while it’s open. 00:04:21.780 --> 00:04:26.130 When it is holding a CD to be played, it is brought into the player and as it reaches 00:04:26.130 --> 00:04:31.389 the spindle, the lower half drops down and this spring-loaded clamp will rest on it. 00:04:31.389 --> 00:04:35.110 The reason why I said the tray might give a hint to the Philips pickup system, is that 00:04:35.110 --> 00:04:39.300 it has a curved cut out to accommodate the path of the laser’s swing. 00:04:39.300 --> 00:04:43.870 That’s a tell-tale sign that the CD player has a swing-arm laser mechanism. 00:04:43.870 --> 00:04:46.920 Now with the disc held in place, the spindle motor spins the disc, 00:04:46.920 --> 00:04:48.820 and the laser will attempt to read it. 00:04:48.820 --> 00:04:53.380 And now we go back to the photodiodes, because this is the really genius bit. 00:04:53.389 --> 00:04:58.330 If the disc is focused correctly and it’s being tracked correctly, all four photodiodes 00:04:58.330 --> 00:05:01.449 will receive the same relative intensity of light. 00:05:01.449 --> 00:05:06.180 This is because the spot of light that’s hitting the array is a perfect circle. 00:05:06.180 --> 00:05:11.490 Due to the optics of the lens and prism, an out-of-focus beam will morph into an ellipse, 00:05:11.490 --> 00:05:15.849 and depending on which way it’s oriented, the focus is either near or far. 00:05:15.849 --> 00:05:20.380 Additionally, tracking errors either left or right will push the spot... 00:05:20.380 --> 00:05:21.789 left or right. 00:05:21.789 --> 00:05:26.699 By comparing the relative intensities between these four photodiodes, the player can determine 00:05:26.699 --> 00:05:29.490 what corrective action it needs to take. 00:05:29.490 --> 00:05:31.110 So what does the comparing? 00:05:31.110 --> 00:05:35.410 Well, when assembled, the ribbon cable which carries power to the laser unit and returns 00:05:35.410 --> 00:05:39.039 signals from the diodes plugs in here on the circuit board. 00:05:39.039 --> 00:05:43.069 Now if we flip it over, we find two rather large chips. 00:05:43.069 --> 00:05:47.069 If we follow the traces from the plug where the ribbon cable went in, there are four that 00:05:47.069 --> 00:05:51.020 go right to this chip, labeled TDA8808T. 00:05:51.020 --> 00:05:52.240 What does this chip do? 00:05:52.250 --> 00:05:56.440 Well, it’s a photodiode signal processor for compact disc players! 00:05:56.440 --> 00:06:00.419 Its data sheet tells us that it is “a bipolar integrated circuit designed for use in compact 00:06:00.419 --> 00:06:03.030 disc players with a single spot read-out system. 00:06:03.030 --> 00:06:07.710 It amplifies the photo-diode signals and processes the error signals for the focus- and radial 00:06:07.710 --> 00:06:09.140 control network.” 00:06:09.140 --> 00:06:10.180 Well ain’t that handy! 00:06:10.560 --> 00:06:14.880 So this chip not only handles the focus, but it also amplifies the actual signal coming 00:06:14.880 --> 00:06:16.360 from the photodiodes. 00:06:16.360 --> 00:06:17.320 Neat. 00:06:17.320 --> 00:06:19.060 But it doesn’t do tracking. 00:06:19.060 --> 00:06:21.560 But if you noticed this strikingly similar chip, 00:06:21.560 --> 00:06:24.540 this one a TDA8809T, 00:06:24.540 --> 00:06:27.000 you might have guessed that this guy does that. 00:06:27.009 --> 00:06:31.639 But it only needs two inputs because it just wants the sums of these two diodes, which 00:06:31.639 --> 00:06:34.800 handily the other chip has generated for it. 00:06:34.800 --> 00:06:39.110 These two chips feed their calculated corrections up to this chip, which actually handles the 00:06:39.110 --> 00:06:43.770 voltage to drive the deflection coils for the lens’s vertical movement and the arm’s 00:06:43.770 --> 00:06:45.100 horizontal movement. 00:06:45.100 --> 00:06:47.880 OK, there’s one last thing that the first chip handles. 00:06:47.880 --> 00:06:52.220 It has some automatic gain control circuitry onboard to actually generate a binary stream 00:06:52.220 --> 00:06:55.930 from what is the analog signal coming from the photodiodes. 00:06:55.930 --> 00:07:00.410 Remember, the pits and lands represent ones and zeroes, but we’re still in the analog 00:07:00.410 --> 00:07:03.710 realm, reading voltage from the four photodiodes. 00:07:03.710 --> 00:07:08.370 So in essence, this chip is an analog-to-digital converter, creating an actual bit-stream for 00:07:08.370 --> 00:07:10.760 the following components to utilize. 00:07:10.760 --> 00:07:15.250 If we follow this trace, from the pin which is labeled “TO DECODER” on the datasheet, 00:07:15.250 --> 00:07:18.500 we’ll find it heading over to this Motorola chip. 00:07:18.500 --> 00:07:22.130 Now this one was a bit of a mystery for a while, in fact it tripped me up so much that 00:07:22.130 --> 00:07:25.600 what you’re looking at now happened a day after what happened before. 00:07:25.600 --> 00:07:30.080 Eh, what exactly the motorola chip does is not clear, as I couldn’t find a datasheet 00:07:30.080 --> 00:07:34.030 for it, but it appears to be the main processor for the machine. 00:07:34.030 --> 00:07:37.939 If you look at these pins here, you’ll see that they head to these connectors which connect 00:07:37.939 --> 00:07:40.289 the main board to the front panel. 00:07:40.289 --> 00:07:44.050 These are likely inputs for the buttons on the front of the machine, as well as the outputs 00:07:44.050 --> 00:07:48.220 for driving the LEDs on the display, though there is probably some communication protocol 00:07:48.220 --> 00:07:52.409 for that task, given there are definitely not enough pins to be driving each segment 00:07:52.409 --> 00:07:54.370 and each indicator directly. 00:07:54.370 --> 00:07:58.560 What is clear is that some of these traces head from the Motorola chip up to the tracking 00:07:58.560 --> 00:08:03.060 chip, which would make sense because if the processor handles button inputs, it probably 00:08:03.060 --> 00:08:06.940 also talks to the tracking chip for navigating around the disc. 00:08:06.940 --> 00:08:13.310 But what’s odd is that the datasheet for the TDA8808T said that pin 10, which is definitely 00:08:13.310 --> 00:08:17.370 this trace, I’ve checked with an ohmmeter, goes to the decoder. 00:08:17.370 --> 00:08:21.440 And this other big chip, from Philips, is called the decoder chip. 00:08:21.880 --> 00:08:23.860 Hmm, what’s going on? 00:08:23.870 --> 00:08:25.659 To be honest, I’m not entirely sure. 00:08:25.659 --> 00:08:28.220 I can make a few educated guesses, though. 00:08:28.220 --> 00:08:32.010 First, if you haven’t already spotted it, you’ll see that the trace from pin 10 on 00:08:32.010 --> 00:08:36.840 the focus chip branched off here, and it also connects to the decoder chip through a resistor 00:08:36.840 --> 00:08:38.400 on the top side of the board. 00:08:38.400 --> 00:08:42.920 So the decoder chip does have a connection to the laser diode’s output, but whether 00:08:42.920 --> 00:08:46.930 or not this is where it’s getting the data it needs is uncertain. 00:08:46.930 --> 00:08:51.450 There are direct connections between the processor chip and the decoder chip, so it could be 00:08:51.450 --> 00:08:55.890 that this trace here is providing the decoder with some sort of redundancy or perhaps even 00:08:55.890 --> 00:08:58.190 something as simple as a clock signal. 00:08:58.190 --> 00:09:02.270 One thing that is certain is that the decoder chip has a number of connections to this chip 00:09:02.270 --> 00:09:03.600 right next to it. 00:09:03.600 --> 00:09:08.170 This chip is a RAM chip, which the player likely uses to undo the cross-interleaved 00:09:08.170 --> 00:09:10.500 reed-solomon coding used in the disc. 00:09:10.500 --> 00:09:15.400 Remember, the data is spread about on the disc in addition to having parity bytes mixed in, 00:09:15.400 --> 00:09:19.250 so the player needs somewhere to dump the raw datastream in the short term for some 00:09:19.250 --> 00:09:21.280 data reorganization and decoding. 00:09:22.040 --> 00:09:25.420 Ah right, that’s probably why it’s called the decoder chip. 00:09:25.430 --> 00:09:30.410 If I were to make a guess, which I am doing right now, I’d say that the processor contains 00:09:30.410 --> 00:09:35.520 the lookup table and is demodulating the eight-to-fourteen modulation used on the disc. 00:09:35.520 --> 00:09:38.630 Then it generates the raw stream of 8 bit words. 00:09:38.630 --> 00:09:43.350 From that point, it sends the demodulated, but still CIRC encoded, data to the Philips 00:09:43.350 --> 00:09:44.600 decoder chip. 00:09:44.600 --> 00:09:49.460 The Philips chip dumps the raw data into RAM so it can reorganize and decode the CIRC error 00:09:49.460 --> 00:09:53.680 correction and recover the actual audio samples from the datastream. 00:09:53.680 --> 00:09:55.620 Then it can be sent to the DAC. 00:09:55.620 --> 00:09:59.580 But the processor is probably also handling the logic of the disc. 00:09:59.580 --> 00:10:04.180 There’s some low-level stuff in the datastream that can be seen before CIRC error correction 00:10:04.180 --> 00:10:05.290 is decoded. 00:10:05.290 --> 00:10:06.920 For example, the subcode. 00:10:07.340 --> 00:10:08.140 Subcode? 00:10:08.640 --> 00:10:10.710 Hmm, have we overlooked something? 00:10:10.710 --> 00:10:12.100 Well kinda. 00:10:12.100 --> 00:10:16.720 We’ve talked in the past about the table of contents and the timecode, but where are 00:10:16.720 --> 00:10:18.490 these along this disc? 00:10:18.490 --> 00:10:23.640 If the CD was just a raw stream of audio samples, how is the timecode being stored? 00:10:23.640 --> 00:10:28.580 Well, earlier I had said that 192 bits of audio samples are stored in a frame, 00:10:28.580 --> 00:10:30.780 consisting of 24 bytes. 00:10:30.780 --> 00:10:33.200 That’s not strictly true, though. 00:10:33.200 --> 00:10:35.420 The frames are actually 33 bytes. 00:10:35.420 --> 00:10:41.170 Now, if you’ve been keeping track, reed-solomon code produces a parity byte for every 3 audio bytes, 00:10:41.170 --> 00:10:45.880 which would mean that in 24 bytes of audio, there should be 8 redundant parity bytes. 00:10:45.880 --> 00:10:48.280 That would bring the frame to 32 total bytes. 00:10:48.280 --> 00:10:49.910 But there’s an extra one. 00:10:49.910 --> 00:10:51.720 Ooh, the plot thickens! 00:10:51.720 --> 00:10:55.910 That is the subcode byte, of which there is one in each frame. 00:10:55.910 --> 00:11:01.370 98 frames comprise the timecode frame, sometimes also called a sector, though the use of the 00:11:01.370 --> 00:11:06.920 term sector was added in the CD-ROM days and is not part of the original Red Book standard. 00:11:06.920 --> 00:11:09.380 However I’m going to continue to use the word Sector 00:11:09.380 --> 00:11:13.200 because “Frame” and “Timecode Frame” are too similar. 00:11:13.200 --> 00:11:19.940 These combine to create 1/75th of a second of audio, so each second contains 75 timecode 00:11:19.940 --> 00:11:25.340 frames, or sectors, which comprise the most specific time references there are on the CD. 00:11:25.340 --> 00:11:28.280 The way the subcode is handled is pretty ingenious. 00:11:28.280 --> 00:11:34.380 Though there is only one byte per frame, a total of 96 frames have a usable byte per sector. 00:11:34.380 --> 00:11:38.240 The first two in a 98 frame sector are used as a synchronization word. 00:11:38.240 --> 00:11:42.350 Now, you might have realized that 96 is divisible by 8. 00:11:42.350 --> 00:11:46.730 So rather than just create one bitstream, each subcode byte actually represents one 00:11:46.730 --> 00:11:49.670 bit of 8 subcode channels. 00:11:49.670 --> 00:11:53.460 Depending on which channel the player wants to read, it will be looking for the nth bit 00:11:53.460 --> 00:11:56.000 in each subcode byte, and stringing them together. 00:12:01.420 --> 00:12:04.680 And the crucial one for the timecode is the Q bit. 00:12:04.690 --> 00:12:08.820 And even within just that datastream, there’s some extra specificity. 00:12:08.820 --> 00:12:13.620 The first bits of the Q channel are actually signifying specific information about the 00:12:13.620 --> 00:12:19.870 disc, and it’s the 72 bits before the last 16 that we need to look into. 00:12:19.870 --> 00:12:24.120 But even then, there are different modes that can be selected within the datastream of the 00:12:24.120 --> 00:12:27.690 Q channel, so there was a lot of thinking going into this. 00:12:27.690 --> 00:12:32.060 I’ve linked the Wiki article on compact disc subcode as it goes over this much better 00:12:32.060 --> 00:12:33.060 than I can. 00:12:33.060 --> 00:12:37.710 This explains the rather elegant way in which a CD player can find tracks on a disc. 00:12:37.710 --> 00:12:41.990 The lead-in contained the table-of-contents (which incidentally is sent in the Q channel 00:12:41.990 --> 00:12:45.520 subcode as well) and the CD player stored in memory. 00:12:45.520 --> 00:12:49.170 It now knows where each of the tracks are by their time code. 00:12:49.170 --> 00:12:53.260 So when you select Track 10, which the Table of Contents told the player can be found 00:12:53.260 --> 00:12:59.220 at this time code, it will first send its laser to around where that timecode probably is 00:12:59.220 --> 00:13:03.220 (after all the physical characteristics are nearly identical from CD to CD) 00:13:03.220 --> 00:13:06.460 and then it simply mutes the audio while it looks. 00:13:06.460 --> 00:13:10.700 By reading the Q channel datastream it knows exactly what it’s looking at, and it will 00:13:10.700 --> 00:13:16.500 move inward or outward in fine steps until it sees exactly the timecode that it’s looking for. 00:13:16.500 --> 00:13:19.160 Then it will unmute the audio, and play the song. 00:13:19.160 --> 00:13:23.600 In a rather smart move, Sony and Philips minded their P’s and Q’s by making these the 00:13:23.600 --> 00:13:27.360 only two subcode channels used in the Red Book standard. 00:13:27.360 --> 00:13:31.720 6 entire data streams were left unused for future extensions of the standard. 00:13:31.720 --> 00:13:36.650 And each of these streams, when discounting the two synchronization bits, can produce 00:13:36.650 --> 00:13:38.990 7.2 kilobits per second. 00:13:38.990 --> 00:13:43.360 Now of course that’s not a lot, but that’s 900 characters of text per second. 00:13:43.360 --> 00:13:48.380 Multiply that by 6 channels and you have 5.4 kilobytes per second of untapped data 00:13:48.380 --> 00:13:52.400 available, or about 24 megabytes total for a 74 minute CD. 00:13:52.400 --> 00:13:55.800 In later years this would be used to produce some nifty things. 00:13:55.800 --> 00:13:57.530 Which we’ll get to, don’t worry. 00:13:57.530 --> 00:14:01.480 But just imagine for a moment how crazy forward thinking that was. 00:14:01.480 --> 00:14:06.800 In any CD, there were more than 16 3.5 inch floppy diskettes worth of data 00:14:06.800 --> 00:14:09.120 sitting completely unused. 00:14:09.120 --> 00:14:13.340 And in 1982, these things weren’t even in commercial production yet, plus they wouldn’t 00:14:13.340 --> 00:14:17.080 hit 1.44 megabytes in size until 1986. 00:14:17.080 --> 00:14:21.150 In a time when hard drives for computers were around 10 megabytes, if you even had one in 00:14:21.150 --> 00:14:27.390 your PC, the idea of having 24 megabytes in one place, let alone 24 megabytes of what 00:14:27.390 --> 00:14:33.410 amounted to unneeded and unused data on a sound storage medium, was quite remarkable. 00:14:33.410 --> 00:14:36.760 But remember, no one was thinking of that at all. 00:14:36.760 --> 00:14:41.290 The CD-ROM was some years away, though it does strike me as a bit of a waste that no 00:14:41.290 --> 00:14:45.620 one developed computer peripherals that could interface with the subcode-out jacks found 00:14:45.620 --> 00:14:50.500 in some CD players to get programs or data off of audio CDs. 00:14:50.500 --> 00:14:51.960 That would have been kinda nifty. 00:14:51.960 --> 00:14:56.090 Now of course, this just an educated guess, but the decoder chip probably isn’t even 00:14:56.090 --> 00:14:57.500 looking at the subcode. 00:14:57.500 --> 00:15:01.430 The motorola chip is probably the only thing paying attention to it, and in fact it might 00:15:01.430 --> 00:15:06.650 even strip that out before sending the CIRC encoded audio data to the decoder chip. 00:15:06.650 --> 00:15:10.670 But don’t assume the decoder chip has an easy job; it’s got a lot of math to work 00:15:10.670 --> 00:15:13.160 out to undo the reed-solomon code. 00:15:13.160 --> 00:15:18.440 Plus, keep in mind that there are 16 bit audio samples here, but we’re dealing with 8 bit 00:15:18.440 --> 00:15:23.230 words, so it needs to decode what exactly each sample is and send this and this alone 00:15:23.230 --> 00:15:24.570 to the DAC. 00:15:24.570 --> 00:15:27.150 Which is definitely the role of this chip. 00:15:27.150 --> 00:15:30.900 Flipping the board back over, if we follow the traces we find we’ve got a couple of 00:15:30.900 --> 00:15:33.840 connections to this little 8 pin chip. 00:15:33.840 --> 00:15:36.610 And believe it or not, that is the DAC. 00:15:36.610 --> 00:15:42.660 This diminutive TDA1543 is all that we need to turn ones and zeros into music. 00:15:42.660 --> 00:15:46.480 Just provide it with a clock signal, your data stream, a power and ground, and you’ll 00:15:46.480 --> 00:15:49.770 get left and right channel outputs on pins 6 and 8. 00:15:49.770 --> 00:15:54.630 Now the datasheet says that pin 3 is the data input, and if we follow the trace back, sure 00:15:54.630 --> 00:15:56.810 enough this heads to the Philips chip. 00:15:56.810 --> 00:15:59.320 So let’s put this entirely back together. 00:15:59.320 --> 00:16:03.660 The circuit board is held down with only one screw, as it also gets support from screws 00:16:03.660 --> 00:16:04.830 on the rear. 00:16:04.830 --> 00:16:09.090 The CD mechanism rests above the circuit board here, and we need to plug in the ribbon cable 00:16:09.090 --> 00:16:13.300 for the laser mechanism, as well as the spindle motor and the disc tray motor. 00:16:13.300 --> 00:16:17.650 The disc tray slides back in place like this, though you have to kind of hold up the moveable 00:16:17.650 --> 00:16:22.070 piece as you do so, and now we’re ready to put the faceplate back on. 00:16:22.070 --> 00:16:25.890 Simply plug in the connectors to its circuit board for the display and buttons, and don’t 00:16:25.890 --> 00:16:29.640 forget the headphone jack, and now we just have to put on this plastic thing which 00:16:29.640 --> 00:16:33.980 connects the power button to the actual power switch, which is way back here for some reason, 00:16:33.980 --> 00:16:36.080 and now it’s more or less assembled. 00:16:36.080 --> 00:16:38.150 Well, except for the cover. 00:16:38.150 --> 00:16:40.051 So now let’s play a CD. 00:16:40.051 --> 00:16:43.380 I turn the player on, and you’ll see that it performs a check of whether or not a CD 00:16:43.380 --> 00:16:44.590 is in it. 00:16:44.590 --> 00:16:47.050 It’s empty, so it enters a standby mode. 00:16:47.050 --> 00:16:51.190 I press the open/close button and the motor pushes the tray open. 00:16:51.190 --> 00:16:55.230 Now I deposit my disc of choice, and press the open/close button again. 00:16:55.230 --> 00:16:59.880 Once the tray has closed, the focus chip performs its initial focus routine, where it sweeps 00:16:59.880 --> 00:17:05.120 the lens from its lowest to highest position in order to detect whether or not a disc is there. 00:17:05.120 --> 00:17:10.029 Once it sees the disc it locks focus on it, and as the disc is spun by the spindle motor, 00:17:10.029 --> 00:17:14.730 it begins analyzing the ratio of stimulation between the two pairs of photodiodes to maintain 00:17:14.730 --> 00:17:17.100 focus even on badly warped discs. 00:17:17.100 --> 00:17:21.470 Now, the tracking chip kicks in, nudging the laser left and right at the request of the 00:17:21.470 --> 00:17:24.009 Motorola chip, which is working for the Philips chip. 00:17:24.009 --> 00:17:27.480 The tracking chip is helping to look for the table of contents. 00:17:27.480 --> 00:17:32.559 Once it’s seen it, it locks onto it and the processing chips load the TOC into memory. 00:17:32.559 --> 00:17:35.430 At this point the player re-enters a standby mode. 00:17:35.430 --> 00:17:39.580 If I had selected play, or pushed the tray in rather than hitting the close button, it 00:17:39.580 --> 00:17:43.049 would have started playing immediately after loading the TOC. 00:17:43.049 --> 00:17:45.269 In any case, it’s ready to play the disc. 00:17:45.269 --> 00:17:50.080 I hit PLAY, and the disc begins spinning while the focus chip maintains focus and the tracking 00:17:50.080 --> 00:17:53.279 chip helps to look for the beginning of the program area. 00:17:53.279 --> 00:17:57.370 After finding it, the tracking chip simply locks on to the datastream, and the raw data 00:17:57.370 --> 00:17:59.490 is processed by these two chips. 00:17:59.490 --> 00:18:02.539 Again, exact specifics unknown here. 00:18:02.539 --> 00:18:06.919 After undoing the eight-to-fourteen modulation, as well as reordering the data and filtering 00:18:06.919 --> 00:18:12.169 out the parity bytes from the CIRC error correction, the player has now extracted the raw datastream 00:18:12.169 --> 00:18:14.070 of audio samples. 00:18:14.070 --> 00:18:17.960 These are sent to the DAC, which recreates the original analog sound wave based on the 00:18:17.960 --> 00:18:20.730 principles of the Nyquist-Shannon Sampling Theorem. 00:18:20.730 --> 00:18:25.049 If I want to select a later track using the NEXT button, the Motorola chip will take over 00:18:25.049 --> 00:18:30.080 the tracking chip once more, nudging the laser farther out while it looks in the Q channel subcode 00:18:30.080 --> 00:18:32.610 for the timecode of the next track. 00:18:32.610 --> 00:18:37.640 Once it sees it, it locks onto the datastream again, and the audio is processed as normal. 00:18:37.640 --> 00:18:41.889 If I select a track that’s far from the start, the laser flings itself out there, 00:18:41.889 --> 00:18:44.700 still looking in the Q channel, for the appropriate track. 00:18:44.700 --> 00:18:49.860 The CD player will happily decode the audio for you until it reaches the end of the last track. 00:18:49.860 --> 00:18:53.509 Now, it’s reading the lead-out, in which the subcode will tell the player it’s reached 00:18:53.509 --> 00:18:55.820 the end of the disc, and it stops. 00:18:55.820 --> 00:18:59.160 Unless of course you’ve got repeat enabled, in which case it’s back to the beginning 00:18:59.160 --> 00:19:01.080 to start the whole thing over again! 00:19:01.080 --> 00:19:03.660 Hooft, that was intense. 00:19:03.860 --> 00:19:04.960 Like the circus! 00:19:05.940 --> 00:19:09.059 Oh no, you’re seeing the CD player all disassembled again! 00:19:09.059 --> 00:19:10.539 The continuity errors! 00:19:10.540 --> 00:19:11.539 The horrors! 00:19:11.780 --> 00:19:13.880 OK, I’ll cut back on the silliness. 00:19:13.890 --> 00:19:18.460 This was my best attempt at explaining how this CD player works in the most comprehensive 00:19:18.460 --> 00:19:22.000 way possible, while trying not to get too technical. 00:19:22.000 --> 00:19:26.500 Already I can tell that this is a longer-than-normal video, so if you made it here, thanks! 00:19:26.500 --> 00:19:27.980 And congratulations! 00:19:27.980 --> 00:19:30.960 Soon, I’ll be taking this back apart-- 00:19:30.960 --> 00:19:32.500 after I reassemble it-- 00:19:32.500 --> 00:19:33.780 and adding some test wires 00:19:33.780 --> 00:19:37.480 to the board so that we can take a look at the waveforms produced by these components 00:19:37.480 --> 00:19:39.080 with an oscilloscope. 00:19:39.080 --> 00:19:42.720 That will probably be the next video on the channel, so be sure to subscribe so you won’t 00:19:42.720 --> 00:19:43.720 miss it! 00:19:43.720 --> 00:19:46.649 Thanks for watching, and I really hope you enjoyed this video, it was a lot of fun to 00:19:46.649 --> 00:19:50.830 make, especially going through the circuit board, finding the datasheets, and all that jazz. 00:19:50.830 --> 00:19:54.679 As always, a great big thank you to everyone who supports the channel on Patreon. 00:19:54.679 --> 00:19:58.740 One of the greatest things about the support I have from Patreon is that it allows me to 00:19:58.740 --> 00:20:02.080 keep the channel going without resorting to outside sponsorships. 00:20:02.080 --> 00:20:06.610 I’d much rather this channel stay entirely community driven, and thanks to people like 00:20:06.610 --> 00:20:08.680 you that’s remained the case! 00:20:08.680 --> 00:20:12.360 If you’re interested in pledging some support to the channel to help it grow, please check 00:20:12.360 --> 00:20:14.039 out my Patreon page! 00:20:14.040 --> 00:20:16.860 Thank you for your consideration, and I’ll see you next time! 00:20:16.860 --> 00:20:20.560 ♫ uncomfortably smooth jazz ♫ 00:20:21.820 --> 00:20:24.460 ...binary stream from what is the analog 00:20:24.460 --> 00:20:28.080 (long pause) 00:20:28.080 --> 00:20:29.180 No, that was right. 00:20:29.190 --> 00:20:30.190 OK. 00:20:30.190 --> 00:20:32.340 That it Reepresent…Reepresents. 00:20:32.340 --> 00:20:33.080 Reepresents? 00:20:33.320 --> 00:20:34.060 Reepresents. 00:20:34.060 --> 00:20:36.160 These continue to create 1/75th.... 00:20:37.200 --> 00:20:37.920 Oh man… 00:20:40.220 --> 00:20:40.960 c’mon! 00:20:40.960 --> 00:20:43.220 But even then, there are different nnmmmmmMMMMMMmmm. 00:20:45.180 --> 00:20:46.340 “modes!” 00:20:46.340 --> 00:20:48.850 ...which the CD player stored in memory. 00:20:48.850 --> 00:20:50.280 It now knows whe… 00:20:50.280 --> 00:20:53.300 (glances at mechanism he just bumped up against) 00:20:55.400 --> 00:20:56.280 or that 00:20:56.700 --> 00:21:01.320 ...plus they wouldn’t be the 1.44 megabytes in size until 1986… 00:21:01.320 --> 00:21:02.820 they wouldn’t… hit… 00:21:04.520 --> 00:21:05.320 dangit.