 Previously Whoa Okay, something just popped. I Still see a little bit of smoke. There's nothing on fire All right. Well, I don't see any obvious signs of damage and I don't think the fuses blue But from the fact that the smoke was coming out from here sort of coming out from under this The only things that are there is you can sort of see those Transistors mounted over here. There are three of them so I suspect that maybe one of them blue, but the other weird thing is that there was a clear spark and That would sort of imply that, you know, maybe there was a loose wire in there so What I'm gonna do is see if I can get under here Now I know that this entire Monitor thing can be removed So here we can see the back of the machine where the monitor sits and this is actually a Module that can be pulled out There are two bolts here and here which basically hold this whole Slighty thing up against these rails. So if I remove these two bolts, I can just pull the entire module out and Take a look at it So here we're looking down at the top of the monitor and we can see that there appears to be Probably a greenish kind of Plastic transparency and a reddish plastic transparency on the bottom So it's also very very dusty People are probably yelling at me right now saying that I just put scratches in the transparency because you should never do that Anyway, I will probably just clean this up with a little bit of a damp cloth And then mark where these lines are just in case the transparency comes off so that I can put the transparency back in the right place Okay, that's looking a little better now that all the dust is off. Let me just put a mark Where the red goes Okay, that way if the thing comes off I can put the red cover back the transparency seems to be held on by I Guess just glue Yeah, actually it looks like Double-sided tape almost so I may just refresh that because you know, I don't know why not Now that this is tipped over carefully because we don't want to break the glass We can see the driver circuitry over here the high voltage circuitry over here and I'm definitely going to discharge the CRT before actually getting in here and working on this What I'm going to do This is nice because the transistors that are heat-sinked onto the sheet metal are connected using, you know just pluggable connectors, so I can remove those and Take this out and check to see if any components are damaged or if any fuses blue with the Plugs unplugged I can also Check the transistors out to see if any of those went bad and were the cause of the smoke Okay, so I have a wire hooked up to a screwdriver Which I'm going to use to get into the anode and Just touch it. Okay So no sparks no nothing So I'm pretty sure that the CRT is discharged Great, so now I can remove the PCB So first things first we have some plugs back here So this is a plug that goes to let's see there are two transformers actually for this plug This one also to trend to Transistors All right, and then we have this is the input plug right here and then we have another plug right over here which seems to go to the To the neck Which controls the heater filament and the gun the electron gun and it also goes to The high-voltage supply, so I'm going to remove this and we finally have another plug That goes to What appears to be I think that's called the yoke? All right, so now we have this ready to go So I am going to let's see we've got some Hex nuts here So I can remove those and there we go PCB So let's inspect this and see what we can find so here's the board I've inspected it and Everything looks fine None of the fuses look bad They all seem to be intact And I don't see any burn marks anywhere or any Indication of smoke damage So I'm willing to bet that there's probably Nothing wrong with this board at least Nothing particularly physical wrong with this board that would cause That sort of sparking behavior Now the sparks Appeared to come. Let's see. I think the board was oriented like this No, it's oriented like this because these plugs are where the transits These are where the transistors plug into and it seemed to me like the sparks were coming from This top area over here, which is where the Transistors were heat sunk or heat synced Let's see. Ah There is possibly a mark here I'm going to take a look a little closer at that okay, well as We can see this is a close-up of the burn mark and we can definitely see Some evidence of blowout basically here So you sort of see that the the smoke sort of traveled in that direction Basically from the pin outwards and it even looks like the corner over here basically got vaporized Now you see this cracking around the solder joint I think what we've got is a loose solder joint which caused that spark So I'm just going to grab the pin and wiggle it Yep, it's totally loose. So what we've got here is a dry solder joint um, which was apparently so dry that When power went through it, uh, it basically cracked, um, or maybe it was cracked to begin with and caused a spark So I'm going to go ahead and re-solder that and I'm also going to look at some of these other solder joints like this one. This one's also loose. So that's not good All right, I've given the circuit board a good going over with solder and IPA Everything looks pretty nice and shiny and All of these connections seem pretty solid I did notice one thing Which is uh, let's see this capacitor here I noticed that it was a bit wobbly and when I looked at The bottom of the circuit board It's going to be a little hard to see. Let's see where that is I think it's right there So if I wiggle If I wiggle it I don't know if you can see, but that is also wiggling. So I applied a little bit of, um extra solder on there So hopefully that will not break Oh, and we can't forget to check these transistors Hmm I seem to have a short circuit possibly I'm going to take a closer look Well, it's actually a pretty good thing that I remembered to check the transistors So here are two Transistors over here and you can see a third one sort of peeking over there and there's a fourth one underneath this bar Uh, this is uh the wire harness that just goes to the transistors And I can simply use my multimeter in diode measuring mode And check To make sure that we see diode junctions So for example, here is one of the diode junctions. So it's showing 0.56 volts And the other way It's also showing 0.56 volts And if I swap the leads If I swap the leads I get nothing Which is what diodes are supposed to do Nothing So that's one transistor. Here's another transistor 0.57 0.57 and if I reverse the leads nothing and Nothing So these two transistors are good. Let's move over to the other two transistors Okay, here are here is one transistor and here is the other And here is the plug that goes to them Now I simply connect 0 volts 0 volts that's not good And even with the leads reversed I get 0 volts and with the other transistor 0 volts And 0 volts So basically both the junctions on these transistors are shot So we've got two bad transistors and two good transistors. So what I'm going to have to do is get a replacement for these two transistors and Sotter them in Okay, so these are the offending transistors the 2n 3715 is an npn power transistor and the 2n 3792 is a pnp power transistor And it's going to be one of these two pairs. They come in pairs One of them drives the x-yoke and one of them drives the y-yoke So the x position and y position of the electron beam or the deflection of the electron beam Now the real question is why exactly did these things spark? One possibility is that they were already bad And that the spark didn't actually Cause these to fail But was actually a result of these failing because if these were basically shorts Then effectively the full current Going through these transistors Would be applied causing Sparks and there was a blowout and the blowout basically shut off the current The other possibility is that the driver of these transistors is bad So what I should do is check all of these transistors to make sure that they're not blown I'm pretty sure they're fine, but I will check them again anyway In the meantime, I do have to order spares of these. I think I'll just order two of each Just in case, you know, I blow out a pair again because I Didn't properly diagnose the problem. So that's what I'll be doing All right, I've finally gotten my transistors in so these are the bad ones And I've got the good ones in here And here one NPN and one PNP. These were pretty expensive. They were a little over $7 a piece In any case, I got two of each There are also these mica insulators So this would fit over the transistor like this And it goes up against the metal of the case. So it's an insulator basically Actually, this would go the other way wouldn't it? Yeah like that So, um, I could reuse these but they do tend to sort of break and rather than Rather than risk having them break. I just bought a bag of them I hope they're the right size. Let's see Okay, I bought a bag of a bag of them And I could only get them in bags of 200. So, uh, Anyway, I'm pretty sure this is the right size. Um It's uh, well, it's it's slightly bigger, but that's okay. It doesn't really matter As long as it fits over the transistor properly. Whoops the other way And the holes line up. That's good enough. So that's an insulator right there All right, so I've got my insulators and I also have heat sink compound Um, they used some white heat sink compound and I also got some white heat sink compound Uh, that just gets smeared all over the place. Um It feels like they've applied it on Mainly the bottom side of the transistor But um, there was also some on the metal case. So anyway, so I have that so what I'm going to do now is just Replace these transistors. I'm going to check the coils that The transistors are attached to let's see So in this diagram, if you can see it, uh, hopefully There's the coil right there and there are the transistors So there's the coil and there are the transistors. Um, when I say coil, I mean the, um They call it, I guess the yoke and it goes over the neck of the crt And its purpose is to apply a magnetic field to deflect the electron beam So one is the x and one is the y Uh, so I just want to make sure that those aren't, uh, like Open circuit And then we'll see Here's where I'm going to put the transistors The 3715 goes here And the 3792 goes here Looking at the other transistors, it does kind of seem that, uh, they put the Insulator on first like so And then they put the, uh Heat sink compound because I'm actually looking at this and I There's a little bit of heat sink compound in there And there's also a tiny speck of dirt that's about to go into the hole, which I don't really want that to happen. So I'm just going to grab that thing Okay, great So what I'm going to do is I am definitely going to put the heat sink compound on Maybe the transistor So Let's put a score up there put a score up there It's probably good enough And now put it in the right way So first I will take the Insulator Put it like that That just doesn't seem right to me somehow um, because you know Well, I guess with um With the insulator being here I guess, uh, it's not electrically connected to the case And I have no idea what what the insulator does for heat transfer. So anyway I'm just going to do it like that. Yeah, actually now that I'm looking at this as it's installed It does pretty much look like this other one In that the heat sink compound is coming out from under the transistor But it's not coming out from under the Insulator, so I guess that's okay All right now This is The screw that holds the transistor in place and also Serves as one of the terminals as well Because there is no electrical connection Between the case and the transistor and there cannot be otherwise the transistor would short out Um, this goes directly into the socket Here is the other one and Did you see where my other insulator went? So now Back inside here I need to reattach The circuit board But first what I want to do is go into these connectors here and make sure that I am seeing the junction diodes And that'll also tell me whether I've connected up the transistor to its socket properly All right, let's have a look So I know that it's grouped Um by three wires, so I'm just going to check Say the first wire and the second wire No, I'll reverse the leads then right and the other junction good And the other transistor let's see Black lead will go in the middle No Do I get that backwards? Oh wait, it's a pnp So the junction is reversed so the red lead goes in the middle Great. All right, the junctions are in Excellent All right, I've screwed these in And interestingly The other side doesn't have screws, but it has these sort of spring clips And it looks like you just sort of push The circuit board onto those spring clips Kind of like that There we go All right, that's pretty secure So here we are looking up inside the machine. This is that cardboard bezel. These are the side windows that spectators can view the game on and It looks like These are actually screwed from the inside So I might just remove them and clean them from the inside Actually, I think I'm just going to leave those windows in. They're just acrylic. They're not glass And I can clean them from the inside. I don't have to remove them so The the face area was particularly dirty So again, we're looking Into the machine from the back These are the windows and the reason I've taken the camera off is to tilt up And you can see that there is actually a mirror. It's at a 45 degree angle So that whoever is looking in Will get the light bounced off that mirror And go down into the monitor which faces upwards like that So I will clean the mirror as well Okay, so I have the camera looking up Into the monitor that way Looking at the board that failed before and now I'm going to Plug the thing in So I'm just checking the safety interlocks to Make sure that they are both Closed so that all I have to do is flip the switch in the back here And now I'm just going to plug it in And turn it on and see what happens. Here we go So what happened was I bumped one of the Uh safety switches and turned the thing off So now with all the safety switches closed, let's turn this on And see what happens All right So far so good I do see that the spot suppression led is on Which Means that there is no signal So that means that there should be no display If there's no display Then it's likely that the problem is now with the logic boards So I guess that's the next thing to look at So I've had to make this totally ridiculous table out of a couple boxes and a piece of plywood Because that was really the only way that I could get the Logic boards out of the machine And place them flat in an accessible area Because of all these cables the way they're the way they're routed So uh and because the switch is now under the table I'm just going to turn the machine on by pulling on one of the safety interlocks I've got my oscilloscope sitting over here And I think the first thing that I'm going to do is Um, there are a couple of test points more than a couple. There's a whole bunch of test points all around these boards Now this is what's called the auxiliary board and this is the main board. It's the one with the 6502 And I was looking here and I see Let's see if I can focus in on These test points Let me zoom out a little bit Yeah, so there's a test point. Let's see. There's various, uh, there's a ground point here There's another ground point here Uh, let's see. There's something called VROM 2 VROM 3 and ROM And VROM 1 these are all active low And I guess those are to Enable the various video ROMs Um, let's see. Ah, this board is called a 6502a analog vector generator Copyright Atari 79 and 80 Uh, okay. Here is a test point called 1.5 megahertz Uh, I think that is the clock That goes into the 6502 Let's see. Uh, here's a crystal The crystal is 12.096 megahertz Uh, so that's definitely one important thing to check that the processor is actually getting a clock Obviously, you know, you'd want to check the voltages as well, which we probably should Um, let's see. Here is a five volt test point and here's something called wd dis I don't know what that means at this point, but I'll figure that out Here is a test point called halt Um, and here's a bunch of test points for the audio circuitry, which No, that's not the audio circuitry. This is the, um, vector Output circuitry. We've got an x center test point a y out test point. That's nice Another ground we've got negative 15 volts and plus five volts DAC Um That's uh, that's actually interesting. So there's uh, some silkscreen over here that says y center Uh I just realized that the video part Is not in frame. There we go. Okay So here's the video output section of the board We have a test point called x center here Uh, we've got let's see y out Ground minus 15 volts plus five volts DAC plus 15 volts and x out um So x out and y out presumably just go right to the the monitor board Uh, this x center is kind of oh, that's not actually x center. That's actually ground Uh x center looks to be It looks like there's room for a potentiometer here. There's another Uh, silkscreen here that says y center And there's another spot for a potentiometer Um Close to those are other potentiometers. So maybe that's what those are Um, this potentiometer here says x bip And this potentiometer here says y bip I guess maybe i'm reading that wrong Um, so anyway and here I think is a button labeled reset So, uh with all these test points Oh, here is a test point called v center Uh, or a v counter probably video counter I should probably look at the schematic before I go trying to interpret these Uh, let's see. Here's a test point for minus for plus 12 volts and here is a test point for minus five volts So the first thing I can do is test the voltages So let's go ahead and put this let's see. Here's a good spot for it Put this on volts Great, that looks pretty good So, uh, what i'm going to do is i'm going to take the oscilloscope probe and do something pretty hokey here And that is i'm going to simply attach the the probe This is very hokey. So I attach the probe Uh, to the ground point along with the voltmeter Okay, um Well, let's turn this on I hope it doesn't blow up and just take a look at some of these voltages over here All right, it's on Everything looks pretty good We've got the uh, the led which is unfortunately off screen over there Let's see if I can rotate the screen a little bit. It's really hard to get everything in frame Maybe just zoom out slightly Okay, I think uh, hopefully you can see that there is the led over there Uh, so we're going to test the plus five volt rail 5.08 volts. That's pretty good. Um, and then the rest is just for the analog circuitry Uh, which we're not really going to test, but we'll just look at the voltages So this is minus five. It's giving off minus 5.2 Uh, this is plus five for the DAC Which is 4.9 Uh, this is plus 15 plus 15 This is minus 15 minus 15 and again plus five for the DAC. Okay So that looks pretty good. Um, great So all the voltages check out the next thing I'm going to do is I'm going to hook up the probe To this 1.5 megahertz clock signal. See what we're getting So conveniently we have a ground lug right next to it And I have to be a little bit careful because there are rails This isn't like covered in, um This isn't covered in, um, solder mask. So All of these silvery traces are conductive All right, so Let's go ahead and zoom out and take a look at the oscilloscope output Okay, there's the oscilloscope output. We can see that we are getting A nice square wave and if we hit measure And I can read that off. We get a v max of 4.16 volts And Where's the frequency? There we go frequency 1.515 megahertz Which is close enough So we definitely have a clock over there. Um, here's a read write signal Let's see if we're actually executing things Well, it does kind of look like we're we're reading and writing Uh, or at least doing something so we've got a waveform Let's see. Here's another test point for phase two That I think is the clock input Yep, that's 1.515. That is one of the Phase clocks that goes into the 6502 So i'm pretty sure that the thing is executing Let's take a look at this VROM VROM 1 Well, I thought I saw something Maybe what I could do is attempt to capture. Ah, there we go. All right So we are getting bursts of activity Yeah, we're definitely getting bursts Yep There we go. Okay Maybe I should just look at the screen and see if anything is happening No, nothing is happening on the screen So now the interesting question is I'm seeing activity on the video ROMs Am I seeing any activity out of the video circuitry itself? So let's go ahead and probe. Well, there's x out and y out That's good enough to tell me whether there is anything Being output. So let's see where is ground ground is right here There's one ground here and one ground here Yeah, okay What I want to measure is Okay, so there's y out and where's x out x out is over there. So I think um, I think I'm just going to use this ground lug here And measure y out Okay, so let's see I don't see any activity Change the scale just in case it's a small signal Well, I see some spikes Well, I see the occasional spike But they're very low signals. Let's see if I'm getting anything out of x out And again, I'm just seeing a few Very small short spikes Out of x out. Let me just hit reset just for fun Yeah, okay, no change So let's see. There's this auxiliary board Which uh, presumably does something and I'm not entirely certain what So what I'm going to do is I'm going to look at the schematic and see what exactly is between the processor and the video output because There's probably a problem Between the two somewhere So that's going to be the next step So I have the schematics and really The big problem with a board like this is that you've got essentially a computerized portion and then the logic portion and I don't know whether the program is actually executing properly We've got the ROMs here We've got some RAM scattered throughout the boards. It looks like there are two RAM chips in one location and something like Six or seven in another location The RAM chips are 2114s And I've kind of heard that sometimes 2114s can go bad And that you can replace them Uh So, you know, unless the ROMs are actually bad and the RAMs are actually bad I'm fairly certain that the program is executing properly because remember again, we did see bursts of activity When we accessed the video ROM So the other possibility is that there's a problem with Some of the logic that feeds into the video generator. So What I can probably do is work backwards from the video generator and tap off each chip using a little clip on device And take a look at the signals for that chip and make sure that Those signals do correspond to the chip's function in other words say if I have an AND gate Well, I want to monitor the two inputs of the AND gate and the output of the AND gate And then just look at all the combinations and make sure that the chip is actually doing what it's supposed to in other words an AND function So that's probably what i'm going to do. I'm going to buy some 2114 RAMs Just in case there Actually is a problem with these RAMs. I'm also going to have to put together a circuit that basically tests a 2114 So that's the next step So I was just probing around the circuit board To take a look at some of the output signals the analog output signal And all of a sudden the machine started making a faint buzzing noise So I went to the front And I see something on the screen It's uh It's obviously Sort of working The text is skewed But at least you can see that things are actually Sort of working So I would say that uh the computer board is probably working fine. That is the the computerized program Um the logic probably is fine So really all I need to do is uh Maybe adjust Looks like the y-axis possibly So that's pretty cool Yeah I'm not really sure why those things are jumping around or if they're supposed to jump around Oh, that was a target reticle Yeah, it's like um something is intermittent here. So I'm going to have to do some further debugging I don't know why this suddenly started working though. It's a bit of a worry I was just basically probing on one of the output op amps I was actually probing on the input Which is the thing that just comes out of the DAC On the x and y And all of a sudden and then I turned it on and the machine started to work. So I'm going to have to figure that one out And also apparently it's set to german So yeah, here is uh my setup the machine is actually uh currently running And this is the output from uh, well, I'm not quite sure which output it is. I suspect it's the y output or rather The input Just before Let's see if we can find it here Um, it's the output of the DAC which comes here And that goes into the input of this op amp Which then goes to this um Amplifier over here and then goes to the y out signal So what you're seeing Over here Is basically the uh y vector signal Now in theory, I guess I could hook up the uh the x on the other channel and uh Put it on x y mode and actually see the vectors come out on this So, uh, that would be kind of interesting to do Again, it was a bit worrying um that it just suddenly worked Well, let's take a closer look at the probe point Sorry for the camera shake, but um, let's see if I can Okay, so that brown thing that you're seeing in the middle of the screen Uh, that is a capacitor That apparently has been put between ground and the input to the op amp Uh, it doesn't appear on the schematics It appears to be uh a later add-on because it's soldered Soldered directly to the chip, which is weird Anyway, I bent it up a little bit and I bent the uh the other one This one right here For the other axis. I just bent it a little bit Um, and then as I was probing it All of a sudden it just started working So, you know, I'm wondering if uh These capacitors are actually bad Whether they should be there in the first place Um, I'm not really sure why they're there But anyway, that's what I found out All right, so uh, let's put this in x y mode and see what happens So apparently the menu is here time base x y All right. Well, obviously there is Something there But it just looks like a bunch of dots because um, I guess we're not Looking at the sweep So how do I uh, it's s a rate I don't know Time base trigger offset. Yeah, there's not there's not much else So I can't really tell what's going on here Yeah, I can't really see what's going on Let's go to Yeah, all right. Well, it was worth the experiment What I really wanted to see is uh, was the distortion caused by The the monitor board or is the distortion actually inherent in Uh, the analog circuitry So clearly some adjustment needs to be done. I just don't know where it does need to be done Okay, so taking a look at the screen again, we can see that I'm pretty sure that the x is working just fine. So I think we can troubleshoot this down to the y axis And I'll show you why When we get the battle zone logo See how it sort of jumps up Now this is supposed to be a smooth crawl. I'm pretty sure So what this says to me is that there's something digital going on I'm almost positive. It's something digital because If it were analog, you wouldn't get those those jumps So it's possible that one of the lines to the deck is not being set properly Maybe some of the um Some of the lines aren't being set or stuck or something. So that's the hypothesis that I'm going to go with So what I'm going to do is I'm probably going to Maybe clip on to well, I don't know if clipping on to the deck chip is going to help me But I can definitely look at each of the signals to see if You know, at least they're all, you know Toggling for all I know, it's the deck chip itself Okay, so we've determined that there's something wrong with the y axis So Here is the schematic For the x and y axes the outputs. So we've got y out over here And we've got x out Over here So we're going to look at the y Coordinate right here And what I want to do is look at the inputs for the digital to analog converter Again, the reason that I think it's uh, something to do with the data lines that are going into it is because there are jumps In the video stream and the y input. So The y output. So I don't think it's any of these components on the output So it's got to be a digital issue somewhere. So what I'm going to do Is I'm going to take a little uh clip And clip it onto this chip And then look at each of the signals and see if they are Toggling or doing things Okay, so this is the chip that I'm interested in. Um, and this is a dip clip Now this is a 20 pin chip and unfortunately I only have a clip for an 18 pin chip So I won't be able to look at all the signals Without actually moving this thing. But basically it just sits Right on there just like that So now I have these pins available and I will use the oscilloscope to look at some of the signals So according to the schematic Um and with reference to the data sheet here What they've done is they've tied pin one to ground And that is the most significant bit This is apparently the numbering is backwards, which is kind of unfortunate. It's backwards from convention Usually, you know, like b zero would be the least significant bit So anyway, you've got all of these bits all the way up to b 11 and b 12 b 12 being the least significant bit So they've tied this to ground. So what that means is basically they're using this chip But they're getting rid of basically half the Half the range Okay, so the first signal that I'm going to look at is the next most significant bit Which is 2 so that will basically tell us whether we're seeing a signal on the top of the screen or the bottom of the screen So let's turn the machine on And I've got the oscilloscope going and hooked up All right, so we obviously see signals Let's uh Increase this a bit Yeah, so I mean there's obviously signals here, right? Oops, I just hit auto That wasn't great Yeah, so there's an example signal There's another example signal And here's wow. Here's a whole bunch of data um, so the timing on this is um, it looks almost like About the smallest pulse that I see is something like five microseconds or less Anyway, let's move on to the next bit down Okay, and we do see Signals there The next bit Signals Next Signals Next Signals so so far so good Next Signals next Signals and This is now b10 I'm seeing signals Okay b11 Signals And b12 Now that is b12 and I'm not seeing any signals whatsoever. Let me just wait a little while Oh, and b12 is grounded. Okay, so they grounded b12 as well So out of the uh, 12 bits they're only actually using 10 But uh, we have seen data on All 10 bits Now just in case I've got my x's and my y's backwards Or, you know, if maybe the coordinate system is the opposite of what I think it is Um, I'm going to clip on to the x chip And take a look at some of its signals. I'm off by the line There we go All right, and um in terms of the uh, the x Let's see I think this no, this is the x right so it goes. Yeah, it's the same thing So the top and bottom bits are grounded So, uh, one bit here Looks fine second bit looks fine third bit looks fine fourth bit fine fifth fine sixth good Seventh good eighth good Ninth Good 10th bit Good and the other bit would be grounded. So it appears that The inputs to the chip are fine But it looks like the output to the chip is not good So what I suspect is that maybe it's the chip that's bad. So what I'm going to do is I'm going to order Uh, a new replacement that might take a little while to come in Uh, and then just desolder this and replace it with the new one and see what happens Here's the block diagram for the digital two analog converter Basically, the idea is that you feed a reference current into this pin Um Provided that this pin is sort of grounded. Uh, there are other configurations But we're just going to deal with the configuration as it is in the machine The negative voltage is connected to minus 15 volts and the positive voltage is set to five volts and uh We have also the outputs now I've connected the um negative current output to ground as it is in the machine And the positive current output to one k Notice that the current is actually going in So basically what happens is depending on uh the Digital pattern that you put on the inputs you will get some multiple of the reference Now if we look at the equation that they give in the datasheet We can see that the full scale reference or the full scale reading I should say Is 4095 which is the largest number you can put in divided by 4096 times four times the reference current that you put in Which is about 3.999 times the reference current now you can see That I've used the 15 k resistor And a 15 volt supply to give me one milliamp of reference current So that means that the output should be able to go between zero and 3.999 milliamps So I've hooked up this circuit Now I've got all of the inputs connected to ground. So basically i'm inputting zero Now I have my multimeter hooked up to measure the reference current So i'm just gonna Turn on the voltage supply And you can see that it's about I have the terminals reversed But it's about one milliamp or so. This is reading microamps. So this is a thousand microamps or one milliamp Okay, and now I've got the current measurement on the output. So let's see what we get with all zeros So it looks like we're getting you know something like zero milliamps So let's Hook the most significant bit up to a one Okay, so I've put a one on the most significant bit. So now I'm inputting 2048 So I should be getting roughly half of four times my input now. I'm not actually getting that I'm getting a little more I'm actually getting 2300 microamps say 2.4 or so milliamps, which is not exactly two So that's kind of odd But let's take a look at what happens if I change the input from 2048 to 1024 I should get roughly half that Okay, so now i'm getting 1070 microamps All right, let me half the number again Okay, and now we're getting 520 microamps. So so far approximately so good Now let's go and have that again Aha So in fact, we're not getting any current at all In fact, it's the same with all of the lesser bits So with each bit that I put in I should have been having The current and that's not actually happening So if we look at this diagram, we see something interesting So we see that the first three bits which actually work go into this decoder And then the other bits go into this network over here So it looks like we actually have the current being set by the most the three most significant bits and then some additional current being put in by this section And they did that in order to save on resistors basically So it looks like the decoder is working, but this section these logic switches are not working Now I fully admit that while I was putting this circuit together I may have screwed something up and I may have actually burned out all of these switches Um, I don't know how I would have burned out all of the switches, but okay um So That's kind of suspicious Now I do have some new chips coming in and what I do put And when I do get them, I will replace this chip with the new chip and see if it reacts the same way Right, so I've finally received from China I've received five of these uh dacks the replacements You can see that they were about four dollars a piece Hopefully they're not you know fakes and uh, it's not unheard of to just take any random, you know dip of the correct package and replace the Replace the markings on it so Let's see Can we even see the markings? So here are the markings on the chip Um, it's a little bit worrying that the date codes on them are from 2009 I was actually not aware of that amd made these chips that late And I'm also not too sure about that logo Um, but you know as long as the part performs like it's supposed to I guess I don't really mind So I'm just going to replace this chip With the new chip and see if it performs better For all I know this is a completely different chip. So let's fire up the machine And see what we get on the output now. I've got the inputs set for zero output And so far that's what I'm seeing zero output now. I'm going to Raise one Okay, and that's actually pretty good. That's um, just about double Uh, the reference current which is 1000 micro amps. So so far so great Now if I lower that and raise the next least significant bit I should get roughly half that which is correct. I'm getting 1000 Now the interesting thing is that the original chip also did approximately the same thing but It wasn't as accurate as this. So it was actually giving more or less So this is pretty promising Now if I go to the next bit I should get half of that Good i'm getting about 500 now. This is where the previous chip failed So i'm going to go to the next bit and I should get again half and I do So so far. This is looking really really promising. Let's keep going Next bit 122 all right Next bit 61 and the next bit 30 And The next bit should be about 15 19 okay, that's not so great But then you know at this low amount of current You know, I don't have an op amp buffer. So it may very well be that the voltmeter itself is actually Doing something And if we go down again We're getting eight And we can go one final step And we get two So i'm pretty happy with this. I am going to go ahead and put this chip into the board And replace the board into the machine and see if we get better output Okay, so now that I've got the boards in I'm going to turn the machine on and see if we get any better result And unfortunately, we are not getting any better result. We're getting what we had beforehand Which is the machine would turn on and nothing would happen So what i'm wondering is if there is maybe some temperature dependent thing going on Or maybe there is just a component that's marginal Or a joint that's bad or something Because otherwise we should see something and i'm looking inside the machine I don't see anything Uh, obviously wrong I see that the uh I see that the spot suppressor light is on which means that we're not getting any video output So I guess the next thing to do is again pull the boards out And see if we can find anything That would lead to this sort of problem So the interesting thing is that The last time I got the machine to work is by having the boards out And by actually probing these op amps over here So the first thing that i'm going to do I think is i'm going to clip on To the DAX to make sure that there is output going on Okay, so let's go ahead and turn the machine off Okay, and install the clip just making sure that that's secure Okay For some reason I can't find the other clip that I used so i'm just going to be using this one And let me clip to a ground lead Okay And I will clip to One of the input signals And now i'll turn the machine on and see what we get Okay, so That's interesting. So in this case, we're now not getting any signal at all It almost looks like We are getting a tiny bit of a signal, but Yeah Pretty much nothing So no input Let's go to the x DAC Okay, that was just because I pulled the lead off We'll go to the x DAC and see what we get Yeah, okay also nothing So let me just Push it some things You never know it could be the socketed chips Ah, there we go. I pressed on this chip right here And it started working Aha There we go Okay That's pretty good. All right, so I think that this chip was slightly unseated And not making good contact So Let's go and take a look at the front of the machine And as you can see we are in business Everything looks great The words are clear if you understand german it basically says One coin two plays insert coin All right, so That was the high score list And there's the battle zone logo Let's just hit start and see if anything happens No, okay, so I need to simulate inserting a coin And this is what it actually looks like from one of the side windows So you can't actually see something. I think that was the moon going by So here we have the coin door. I'll just open it up And somewhere in here, let me move the camera so you can see a little better Okay, and somewhere in here. We should just be able to pull on Something to simulate a coin dropping And it's usually somewhere around the bottom of the mechanism There's like a little bit of metal wire. Let's see Actually, this is the coin mechanism right here There's a piece of plastic here and that was one of the things we found in the machine when we first opened it up So let's see How do you make contact? I don't think that did anything. Let's see. Let me see Okay, I don't know what that is Let's see All right, this is some micro switch here There we go. I think that was a coin. Okay, I hear clicking of a relay. Yeah, okay So now it's saying in German press start button Okay, so there's the start button And let's see what happens when I start The joysticks Don't really see anything moving forward with the joysticks Hit the fire button Oops, apparently I was hit interesting. I thought that was supposed to be terrain showing up You know, like if I turn around Well, okay, so there's the moon. I can certainly like drive towards the moon Okay, so somebody's shooting at me Don't just spin in place Um, it's almost as if Yeah, so it's almost as if um There are some game elements which aren't showing up. I know that they're supposed to be background mountains And of course, you're supposed to be able to see Some of these shapes that shoot at you So I didn't see any of these shapes. I saw the moon. I didn't see the mountains And I think I did see Missiles being launched from whatever these things are So, well, that's the next thing to take a look at