The Selection Accumulator; a Jukebox's Brain

Last week we explored the record changing mechanism in this… charmingly ugly, stylistically repressed clunky buzzy disc jockeying gizmo box of horrors. We looked at the mechanical bits that grab the record, manipulate the tone arm and turntable, and all that jazz. We also created a circuit with a relay to start and stop an action with two separate inputs. Also known as buttons. Yeah, I’m gonna try to explain that a little better in this video, but anyway if you haven’t seen the video that I’m talking about right now, you should probably consider watching that first. In fact, here’s a card! I’m just kidding, there you go. And for all those situations where cards don’t work, there’s a link in the description. Of course this is upside-down, but we’re gonna roll with it. I left you with a devastating cliffhanger. You see, we covered how this machine is able to take a record from the record carousel and play it, but we never covered how exactly it knows what record to play. Well, that’s what we’re gonna cover in this here video. Shocking, I know. So let’s consider what needs to be accomplished. We don’t have the luxury of a computer; we only have a few relays and whatever sort of mechanical contraptions we might devise. How could you design a sort of memory to store a selection to be played given those limitations? Why with a ridiculously complicated electromechanical solution, of course! And.... THIS is it! Exciting, huh? This is the Selection Accumulator. This device functions as the memory of the jukebox. Calling it memory is a bit of a stretch, as you’ll soon see, but it does store selections to be played. Just, in physical space. Using physical objects. You’ll notice that all around the edge of this are a bunch of little metal pins. They each have a spring attached to them, well most of them anyway, and they’re labeled just like the selections of the jukebox. See, each of these pins is a selection. There are 200 in total, starting at A1 and ending with V0. By the way, if you noticed that the letters I and O were missing, that was done just to prevent confusion between those two letters and 1 and 0. Take a closer look at the springs and you’ll see that they’re all under tension. Right now, these pins are just barely staying held down. They’re really on the edge of their seats. If you push one ever so slightly towards the center of the… let’s call it a basket, it will suddenly pop up. [click] That sounds like a click I’ve heard before! Anyway, thanks to the spring it will stay in the popped up position until something pushes it back down, and then it will be caught on the edge again so it stays down. So, let’s say you had selected C5. Well, in that case, the pin for C5 will be popped up. And then the jukebox knows to play C5. If you have questions regarding how the pin managed to become in the popped up state, or how that translates into the jukebox actually playing C5, stay tuned because I’m about to answer them. But first, buttons! And I do mean buttons. The selection buttons up here on the top of the jukebox are what makes those pins pop up. It’s really fascinating. So, firstly, recall from the last video that when you push in these buttons, they stay held in until the selection accumulator has done its thing. This serves two functions: One, it’s how the jukebox keeps you from making selections unless you’ve put some money in it, and two it creates a circuit across the letter and number patches. Hold that thought, we’ll get back to it. Way up here is the Latch Solenoid. This must be energized in order for a selection to be made. If it’s not, as is the case when the jukebox is turned off, you’ll see that the buttons do not stay down. Unless the jukebox’s Credit Accumulator, which unfortunately does not work on this machine, registers a credit, this solenoid will not be energized and you cannot make a selection. And before you think of getting all crafty and just holding them in for a bit, the latch solenoid also moves these various leaf switches, setting up other circuits that come into play. So you cannot possibly make a selection unless this solenoid is powered. The latch solenoid is held in by Relay 1, one of four relays in this junction box. The junction box is mostly just a box that a lot of things plug into. Basically it’s just a bunch of wires in here going from socket to socket, but these four relays handle some of the various shenanigans we’re about to see. Anyway, relay 1 receives power from the credit accumulator. This is the device that counts your money. Here’s a brief look at the credit accumulator. Again, it doesn’t work, I’ve not been able to make it work, but what it’s supposed to do is add and remove credits from the machine based upon which selections you make and which coins you insert. Were it working it’s surprisingly versatile, allowing you to set the number of credits each coin gives you, and even do things such as require two nickels for one credit. It’s wired to the coin mechanism down here, an equally fascinating bit of tech, which validates and sorts nickels, dimes, quarters, and even half dollars, all done by gravity alone. Missing from the machine at the moment is a blue plastic coin chute which would direct coins from the slot up above down to the top of the coin mech. Anyway, depending on the coin it would fall onto one of these four switches, and that would - or should anyway - make the credit accumulator count up however many credits you set it to with these levers and junk. Anyway, again; it doesn’t work, which is a bummer, but thankfully someone has rigged this machine to simply always behave as though it has a credit. So, relay one is energized, and therefore so is the latch solenoid, whenever it’s powered on. OK. So, back to the buttons. With the latch solenoid held in, press one letter and the button will stay depressed. You can see the latch mechanism through this hole in the top of the jukebox that definitely shouldn’t be there but it is anyway. By the way - don’t think of any funny business and try to select two letters or two numbers at the same time. Wurlitzer’s way ahead of you - the lower one will get priority. Anyway, press a letter, then a number. So again, C5. A lot is about to occur in the next two seconds. Strap in. Once both a letter and a number are selected, these leaf switches will energize Relay 2, which is one of the relays here on the junction box. Interestingly, the junction box has different names for these four relays, despite the fact that the service documentation only refers to them by numbers. Anyway, the closing of relay 2 completes the circuit to the selection accumulator motor. That’s this guy! You may have noticed this weird thing sitting in the middle of the basket. Well, when you make a selection, this goes for a spin. A 180 degree spin, in fact. And you know what makes that happen? Why, Relay 3! Heyo, it’s time for that button demonstration to come back into the fold. But this time - it’s not a button. It’s a circuit board. Notice what happens when I give the little spinny thing a push. It suddenly starts moving, then stops again. How’s that happening? Well, notice these contact patches. You’ll see that there’s a break in them on both sides. Well, this one’s not really a break but hey, let’s not get pedantic. That’s my job. On the bottom of this arm are four wiper contacts. These two here provide power to relay 3. Now, at rest, the circuit is broken. So, relay 3 is de-energized, and the motor doesn’t get any power. But, if I push this far enough to where the wipers touch the patches, relay 3 will close a switch contact inside itself, powering the selection accumulator motor. The motor will stay powered through a 180 degree sweep, so it will keep spinning, but once the contacts make it off the patch, the relay opens the switch, and the movement stops. Now, you saw that I needed to give this a push to start it going. But after that point it completed its task on its own. Relay 2 is what gives it that initial push. That happens as soon as both a letter and a number button are pressed in. Once it’s moved from its starting position, relay 3 takes over. And once it’s made it to the end of the rotation, relay 3 is released, and the motion stops. Oh and by the way, all these other contact patches did various things, including removing a credit from the credit accumulator (if it were working) and releasing relays 1 and 2. OK, now we are not getting deep into the specifics here. This is how relays 1, 2, and 3 are represented in the schematic. It’s nuts. This is very difficult to follow, especially since you have to go from one page to the next to make sense of anything, so for my descriptions of what’s going on here I’ve been relying on the much more helpful Sequence of Operations section of this lovely service manual. Now, in regards to the red and green button demonstration from before… well first let me acknowledge how unsatisfied with that explanation I am. I really should have been more specific about what the buttons were accomplishing in the circuit, and a schematic would probably have been helpful at least to some of you. So, this time, no buttons. Ah crap, but this all gets started ‘cause of the selection buttons! Ugh. Well... Basically, and I’m not promising or even trying to achieve perfect accuracy here, when both a letter and a number button are held in, these weird linkages cause one of these here switches to energize relay 2. Inside relay 2, a pair of switch contacts closes which provides power to the selection accumulator motor. So it starts spinning. Once it’s moved out of its park position, this track here energizes relay 3. Relay 3 also has a pair of contacts inside of it that provide power to the selection accumulator motor. Now, relay 2 can be released without stopping the motor. So, relay 2 got this going, but once it left its park position, it could keep going on its own because of relay 3. Now, I’d love to get into more of the specifics regarding these patches, but... unfortunately I can’t make any sense of how they relate to the other things that are going on. For example, remember relay 1? Well, that guy is supposedly powering the latch solenoid, based upon whether or not there’s a credit in the credit accumulator. But power to the latch solenoid has to be released briefly when the selection accumulator stops in order for the selection buttons to pop back out, and I can’t say exactly what causes that. Does relay 1 momentarily get de-energized thanks to one of these patches? Or is the solenoid itself powered through here? I don’t know, and I’ve been staring at these schematics for hours, and my brain hurts. All I’d like you to see here is how we can make a bunch of things happen in sequence by running some contacts over some patches. This is yet another kind of program; I hesitate to say this but it’s a lot like a series of buttons that are getting pressed automatically in sequence. Yes, these aren’t buttons, but they’re sets of contacts getting bridged as the wiper runs past them, one after the other. So, it can cause various actions to occur at various times, depending on how and to what these contact patches are wired. This is what electromechanics are, people. It’s a buncha wires, all going to different places, and all through different things. And now to the most important thing of all. The pins. So, this spinny thing is officially called the Shaft and Magnet Assembly, and on both ends you’ll find a Selector Magnet. This is an electromagnet which travels just behind each of the pins. You’ll notice that down here are a pair of wiper contacts, and they are travelling over all of these teeny tiny patches. This is where the real magic happens. Each of these thick bars on the inner edge is wired to one of the letter buttons. So we’ve got A over here, B is next to it, and so on all the way through V. These teeny tiny patches along the edge are wired to numbers 1 through 0, and they repeat over and over again. Looking on the bottom you can see how there are wire links connecting every tenth patch together. When two buttons are pressed, there’s power across one of these letter patches, and twenty of the number patches. See where this is going? When you’ve selected C5, the C patch and all of the 5 patches become a power source for the electromagnet. I’m not sure which one is live and which is neutral, and in fact this is an AC circuit so it doesn’t really matter anyway, so let’s just say there’s voltage across the two of them. As the magnet arm sweeps, the electromagnet is just chillin' doing nothin'. Sure, there’s voltage on all of these 5 patches, but there’s nowhere for that voltage to go. Except at C5. Right when the electromagnet is behind the pin for C5, it gets a brief pulse of power, pulling the pin towards it, which causes it to pop up with the help of the spring. Isn’t that just the coolest thing? With one letter and one number, there’s only one spot on this entire board where a circuit is actually complete between the inner and outer rings. The reason there’s an electromagnet on each end of the arm is that it only rotates 180 degrees per cycle. Now, the very last thing this mechanism is responsible for is providing a pulse of power to the Override Magnet. That’s this guy. The override magnet pulls on a little latching mechanism to close this leaf switch. This switch is essentially the master power switch for the entire record changer. So long as it’s closed, the carousel, Wurlamatic, and all their associated doodads now receive power, so it can start looking for the record to be played. And how does it do that? Why, with the Readout Arm, of course! This is what I said connects to the black bar underneath the record carousel in the last video. The readout arm is what actually translates the popped up pin into a record to be played. You can see it has these little feeler levers connected to two switches. When the selection accumulator is installed in the jukebox, it hangs directly underneath the record carousel, and the feelers of the readout arm travel right above the pins as the carousel rotates with the motivation provided by this motor You may have noticed already that every other pin is shaped differently. All of the odd selection number pins have a notch in the side facing the outside edge, and the even number selections are the opposite. That’s so the correct feeler is activated depending on whether the selection is the A side or the B side of a record. See, these two pins are both the same record in the carousel. That’s why readout number 2 is resting farther forward than 1 - they need to stop the carousel in the same place, but the pin for side 2 is farther ahead in the rotation. Side-note; It annoys me greatly that Wurlitzer refers to everything as Side 1 and Side 2 when it has long been established that 45’s have an A side and a B side. In case you haven’t been doing so this whole time, please note that Side 1 corresponds to Side A, and 2 corresponds to B. I don’t really know if Wurlitzer was trying to alleviate confusion with selections A and B, or if they had some other reason for not calling these Readouts A and B, but here we are. Anyway… These two readout switches are connected to this contact board up top via these feelers. Fun fact! These are my biggest source of problems with this machine. You’ll notice that a few of them are all bent out of shape, and only some of that was my doing. These contacts need constant cleaning in order for the jukebox to work correctly, as the timing of when these feelers hit the pins and thus stop the carousel needs to be fairly precise. Now, you may recall from the last video that the side one and side two relays were what started the Wurlamatic mechanism and thus pulled a record out of the carousel to be played. Well, these are what they’re wired to. If readout 1 gets tripped by a selection pin, that energizes the side 1 relay, which stops the carousel, activates the Wurlamatic, and also energizes the side 1 solenoid so that the record takeout arm’s left pin gets caught by this catch, and it pivots into position to play side one of the selected record. The same thing happens when the side 2 relay is energized by readout 2, although the side 2 relay does not energize the side 1 solenoid, therefore causing the take-out arm to pivot in the opposite direction. So then, here’s a question a few of you have probably been asking by now; How does the pin go back down? Aha! Well, that’s not the job of the selection accumulator. It has no ability to reset the pins. But, the readout arm does! There are a pair of small solenoids on top that are attached to these little metal pusher things. Thanks to a switch buried deep within the Wurlamatic mechanism, called the cancel switch, these solenoids briefly get power during the course of its rotation and push the pins back down. One of the key components that I haven’t mentioned yet is the Magazine Lock Solenoid. That loud buzzing it makes as the carousel turns is coming from this. It probably shouldn’t be that loud, but the machine is 50 years old, cut it some slack. The reason it’s important is that it aligns the carousel whenever it’s stopped with this spring-loaded pin. This not only ensures ideal alignment with the records and record take-out arm (and its grabby thing) but also with the cancel pins of the readout arm. Ideally, the feeler switches will be adjust so that the carousel stops a bit prematurely, and the lock solenoid pushes it a little bit farther. This ensures the readout switches are firmly against the pins and make consistent contact. Now, here’s where the cleverness of electromechanics comes into play once again. You’ll notice that only one of these cancel solenoids moves. And there is only one cancel switch inside the Wurlamatic to make that happen. Why didn’t they both move? Well, because the current path between the cancel switch and these solenoids goes through the side 1 and side 2 relays. Only the solenoid representing the side currently being played receives power, thus only that selection is cancelled. It’s simply a matter of running the power through one of the normally open contacts of the relay, so that whichever relay is currently being energized (thus, the side that’s being played) will provide a current path to the corresponding cancel solenoid. You might then ask, what happens if someone selects both sides of the same record? Won’t the side one and side 2 relays both be energized? Well, no! Why? Because side 1 takes precedence over side two. How? Because the side 2 relay is wired through a normally closed switch contact inside the side 1 relay. In this way, side one and two are interlocked. If both of the readout switches are activated simultaneously, both relays 1 and 2 are receiving power. But, if relay one is energized, it cuts off that power to relay 2. This in turn means that the Wurlamatic will grab the record, pivot to play side one, and cancel the side 1 pin and the side 1 pin only. Because remember; Relay 2 is not powered whenever Relay 1 is. Relay 1 disconnects power from Relay 2. So, down comes the cancel solenoid, with its power output being directed through relay 1, and now once the cancel solenoid is released the side 1 readout is released as well. This now de-energizes the side 1 relay, which means, now the side 2 relay can be energized by readout 2. The result of that is that once side one has been played, the tone arm will hit the trip switch, the Wurlamatic restarts to put the record back, but with the side 2 relay now energized, the transfer switch is out of the picture and it immediately takes the record back out again. This time it pivots to play the other side. Now, when the Wurlamatic hits the cancel switch for the second time, the other cancel solenoid fires, and puts the side 2 pin back. Now neither readout switch is activated, and so neither are relays 1 or 2. When side 2 is over, the trip switch is hit, the Wurlamatic starts back up, and without the side 1 or side 2 relays in play anymore, as soon as the record is put back, the transfer switch stops movement of the Wurlamatic, the record jaw thing hits the safety switch, and the carousel starts rotating, looking for the next pin and thus the next selection. Once the carousel has made one complete rotation, this catch on the end of the readout arm hits the latch mechanism near the override magnet. This doesn’t yet open the override switch. Instead, the carousel will go on for one more rotation. This is done in case it was, say, playing F3 and you then selected C2. C2 is behind F3 so it's gonna hit this before it gets there. Once it hits the override mechanism a second time, that switch will open, and now the jukebox is back to its standby state. Did you get all of that? It’s simple, right? Let’s go through all this once again, just for funsies. We begin with the latch solenoid. The latch solenoid is held in because the machine thinks it has a credit so relay 1, which is different from the side 1 relay - why did Wurlitzer do that? - is energized. Pressing a letter button and a number button closes these leaf switches which in turn activates relay two, which gets the selection accumulator motor started. Once the magnet arm leaves its park position, the wiper contacts will complete a circuit to relay 3, so it will keep going. The combination of letter and number puts voltage across the letter and number patches on the board of the selection accumulator. Once the electromagnet is behind the corresponding selection pin, the magnet fires, pulling the pin towards it, unseating the pin from its catch, and it pops up. When the magnet arm is back at its park position, the circuit to relay 3 is broken, which stops the magnet arm. At the same time, power is interrupted briefly to the latch solenoid somehow (still not clear on that one) to pop the selection buttons back out, and a pulse of power is sent to the override magnet, closing the override switch, thus causing the carousel to be unlocked and begin rotation. Once either readout switch hits a pin, this energizes its corresponding side relay. That will cut power to the magazine motor and its lock solenoid, locking it in place. It also provides power to the main cam relay, causing the Wurlamatic to remove the record from the carousel. Shortly after it’s moved, the transfer switch keeps the main cam relay powered, which is important because the cancel switch will fire the corresponding cancel solenoid, pushing the selection pin back down, and thus de-energizing the side one or side two relay. At this point, the carousel will not be able to move because the safety switch is not being depressed now that the record take-out arm is away from its parked position. Once the record take-out arm is in the play position and the stylus has been moved to play the record, the play switch is depressed, pausing the movement of the Wurlamatic by de-energizing the main cam relay. Now the record can play. When it’s over, it hits the trip switch, bypassing the play switch and re-energizing the main cam motor once more. Now the record take-out arm will return to the record carousel, and assuming the pin was successfully cancelled and thus neither the side 1 or 2 relay is still being energized, the record grabby jaw thing will open up, hit the safety switch, and the carousel resumes movement. If another selection is stored in the selection accumulator, it will of course stop once more and repeat the same sequence. However, if there are no more selections, the carousel will hit the override assembly once, and make one more rotation. After completion of the second rotation, the override switch is opened, stopping the carousel, and now the jukebox is back in standby mode. So. Is this neat or what? I mean, wow. I love the way this thing works. It’s endlessly fascinating to me, and even more so when you remember that there is not a single programmable logic controller residing in here anywhere. Speaking of, I’d like to address a bit of apparent controversy with the titling of the last video. And possibly this one. I don’t consider this device to contain a computer. But, some people would say that it is a computer. I disagree, but first let’s acknowledge that electromechanical computers are a thing! There’s no reason you can’t create a fully-functional computer using nothing but relays. But, I don’t see this device as computing anything. It has a set of instructions, sure, and what do computers do but follow said instruction sets? But at the same time, would you call an internal combustion engine a computer? It has a cam shaft which opens its valves in time with the movement of the piston. And in that sense it was programmed, but the actions are entirely mechanical. There’s some nuance to be explored here, but I would consider a sequence of operations to be separate from computing. Now, you could kinda argue that this machine does multiplication in the selection process… but I don’t know if I’d agree. The one thing it does actually compute is the value of coins. I would consider the credit accumulator to be an electromechanical computer, although a very basic one. And even then, it really just counts up and counts down, with each step being controlled with relay logic. And that’s where this gets messy. This machine is undeniably full of relay logic. In that sense this does have a programmable logic controller. The programming was just done in what today we would call a very unconventional fashion. Perhaps it would have been better to say silicon-free computing, but let’s be honest. When you say the word “computer” these days - this is not what comes to mind. Well, thank you so much for watching! I hope you liked this video. To answer a question I’m sure many of you are wondering, yes. This is my jukebox, and I’ve had it for years. It’s been at my parent’s home all this time, and also kinda non-functional for the past half-decade, which is why I’ve never featured it. One thing I do need to track down are suitable replacement springs for the selection accumulator. A number of selections just don’t work because the springs were broken, likely since the bottom panel of this machine has always been missing. The broken springs are all on the side that faces the rear, suggesting they were damaged through careless handling. This jukebox is actually what turned me into the weirdo I am today. My parents let me buy this thing when I was in - wait for it - middle school. Yeah. And I could afford it with my chores allowance because it was very ugly and very broken. The person who owned it previously didn’t have any interest in fixing it, so it went on eBay for cheap. I owe my parents a lot of thanks for things that have happened throughout my life, but their willingness to let me buy a broken jukebox at the age of 13 is certainly high up on my list. So, thanks mom and dad! And now, it’s time for me to end this video. But! There are a lot of interesting features of this jukebox that we haven’t covered. Be on the lookout for a third jukebox video at some point, but for now, thank you. Thanks for watching. Thanks to everyone supporting this channel on Patreon. And thanks again to my mom and dad. Cue the music! ♫ gratefully smooth jazz ♫ We’ll make one more take of that… then we’re moving on. ‘Cause this is a LONG video. I left you with a devas… eugh. Gonna be doing this ‘till like 1:00 in the morning. This... oh sh*t… sh-oops, I said a bad word… One more take of that. Ths only weights like 15 pounds, and has sharp edges, no big deal at all That’s a longer line than I thought, my word That’s so every corr… every? Where did that word come from? Well it was earlier but not there. From my descriptions of what’s going on here, I’ve been relying on... And I forgot to put my finger in the thing. Ohhhh boooyyyyy… So, how confused are you? Seriously, I hope that wasn't too bad. Also, totally wasn't thinking about how much these captions would get in the way of some things on-screen. Pro-tip! On desktop, you can click and drag these captions around to wherever you'd like. So there's that. Sorry, mobile users :(

Channel: Technology Connections

Views: 1,190,268

Keywords:

Id: o1qRzKuskK0

Length: 28min 52sec (1732 seconds)

Published: Sun Mar 22 2020

Reddit Comments

[u/knockknuckles]

Really impressed with the detail of this video. Clearly shows a lot of time went into it.

[u/faraway_hotel]

I don't think I've ever heard a more fitting description of 70s design than "charmingly ugly, stylistically repressed". Not all of it, but there's a subsection this 100% applies to.

[u/beanmosheen]

Can we have a scan of the schematic?

[u/chaos_a]

On the jukebox at 3:26

I have no idea what this light is for

and

I FINALLY FIXED IT

u/TechConnectify how did you make such authentic looking stickers? Just plain printer paper?

[u/KingOfTheP4s]

This would make a nice segway in to an electromechanical pinball machine!

[u/BigMacTMMM]

How do we get the man himself to see the offer to supply parts that Nick Jabbour made on YouTube?:

I bought out the remnants of a TV and radio repair shop whose hay day was ca 1960s and 70s.

Get in touch and I’ll get you those springs and relay, no charge.

Lots of resistors and switches and solenoids.

This could be the distraction I need.

That's going to unlock the third Jukebox video. It needs to happen!

[u/Trans-Europe_Express]

This video reminded me of the enthusiasm and clear explanation in classic engineering documentaries like this https://www.youtube.com/watch?v=x4maPt3qFI4&feature=youtu.be