 It's two weeks later. My new op-amps have arrived. While waiting for these things to show up, I have reviewed the footage and I now have a much better idea of what's going on. Putting this chip on upside down has caused a dead short through the power rails, which is plus and minus 12 volts. These go through this defunct 10 ohm resistor and this 10 ohm resistor, which has survived. Now if I look at the footage in slow motion, you can see this distortion around the two resistors. I originally thought that was evaporating IPA, which had been trapped under the component. That is not true. What you're seeing there are the power rails actually buckling from the heat. This is not good. Luckily the lower resistor, this one, popped before too much damage was done and I think we're okay. This one seems to be all right. It still registers as 10 ohms. So I'm going to replace this with a discrete resistor. I have a bunch and I'm going to replace the op-amp here with one of my shiny new ones and hope that things still work. And of course, I'm going to have to take this capacitor off again because I don't think there's enough clearance here. Although it's probably worth a try. I still have my piece of foil. So time to get the hot air gun out and give this another go. So now that thing came off, which wasn't nearly as hard as I thought. Let's check the continuity of those power rails. So that should be here. And the meter says 0.0 ohms. That's good. And I'll show this one. Zero ohms and this end 10 ohms and this end nothing. No connection. Excellent. So as far as I know, that looks okay. I haven't checked for damage up here. There's a via there. There's this big, thick track here. You can see. Remove that a bit. So this will be fine, but this side. Let me just put that into beeper mode. And okay, that looks okay. Although I'm a bit perturbed that it's so easy to make contact there. I wonder if it's burnt the solder mask off. Anyway, that looks fine. So the next step is to put the right chip on. That's the dead one. Notice the notch here. There's the square that indicates the footprint. There's a notch there indicating what pin one is. I put this on this way around with this hole indicating pin one at the wrong end. That should be the other way around. So if I can pick this blasted thing up before I do that I think I'm going to try to put this on properly using the hot air gun. Given how much difficulty I had soldering the damn thing on with the soldering iron, this might actually work better. Okay, let's try this. First, let's get out our new hopefully working op amp out of the very much non-static bag. So this I bought three just in case. Needs to go on this way around. Now this does not have the little hole in it, but it does have a a bar across one end and you can tell by the way the text is up. And we'll just actually take a quick peer at this close up. LF 347. Okay, that should do. So I've also got this. This is solder paste. It's the first time I'm going to use solder paste. So we want to put a very small amount. Let's try this side first. It's a syringe, so and I haven't used it before. So the nozzle is full of air. I need to prime it. Okay, we have solder paste. So this gets smeared across here and across here like that. Tiny amount. And then I place this on the pads and line it up. And the solder paste is slightly sticky, so it actually helps keep it in place. And then I toast it and with luck magic happens. Okay, So as you saw, as the solder paste heated up, it self-wicked itself under the onto all the pads. So I didn't have to solder them all manually, almost like magic. Unfortunately, just like magic, it didn't quite work. So we've got a bridge there and there. And also some of these connections didn't quite work. That one doesn't work. I'm not sure about that one. These worked or or not, actually. That one works. So I'm going to have to go over this with the soldering iron anyway and try to fix it all. Well, I fixed the bridges. At least I thought I'd fixed the bridges until I did this. So I think something is awry underneath that. So time to fire up the hot air gun and take it off again. Yay. Yeah, there's a monster blob of solder here. I don't see anything here, but there's just general goop. So time to clean it all off again. However, looking at the schematic, I can see that pins one and two of the op amp, which are these two, are connected together. So that wasn't a bridge joint. And likewise, pins six and seven that are these two. One, two, three, four, five, six, seven, these two are connected together. However, I noticed there was a bridge between pins eight and nine, which are connected together via a resistor and a capacitor. So nothing. So there was in fact something wrong with it. So we are going to have to clean up the op amp a bit just to get the solder blobs off it and try again with the flux paste, I think. So I think that worked. I did have one bridge I needed to deal with. However, while working on it, I spotted. Can I get this off? A very thin strand of copper wire that came loose from the solder braid, which I need to get off. So I think I got it. I don't see it anymore. So now it's time for that 10 ohm resistor. Which is supposed to go here. As you can see, it is kind of huge compared to the actual pads. So what we're going to do is cut one leg here and then place it here and curve the top leg round to touch the other pad. So this solders on here like so. And this curves around and down. I think that needs to cut about there to here. Okay, I think that's done. Now that little piece of wire did flick off somewhere. There it is. We do not want that on the board when we do our testing. So assuming that nothing else is wrong, and I haven't like cocked things up again, I think this is now, shut up, now ready for testing. So, reach over for the power switch, watch these resistors carefully, nothing's happened. Good, nothing dramatic anyway. I did not plug the, I forgot to plug the floppy drive in, so it didn't actually boot. So let's zoom back out again and try that again. So hopefully it should boot. There we go. The computer is running. Okay, press F5 for music. Sounds better. Press F5 again to sine wave. Nope, it is still nagged. Fantastic, well that's special. So what you're looking at here is the output hooked up to the oscilloscope. I noticed when I was listening to it through the headphones properly that the volume was not actually that different, but the timbre was very different. So I finally got everything hooked up and what do you see? A nice sine wave on the white channel and this whatever is on the red channel. So I think something is terribly wrong with the filtering. What's particularly interesting is if I turn on the Amiga's own filter, I get that, which is also different. Okay, so I've got the scope hooked up and using this slightly homemade probe, let us start doing a bit of diagnostics. So the first thing to do is to check the op amp voltages. So that shows plus 12 and that shows minus 12, which is what we expect to see. Okay, so let's try some signals. The output from the left hand filter is on pin one and that shows our freaky square wave that we don't want to see. So the left channel is bad. The output from the right channel is on pin seven, three, four, five, six, seven. And that shows a nice crisp sine wave. Okay, so that's the output for the op amp. About the output from the filters. So looking at the circuit diagram, the input from the second stage is on pin three for left square wave and pin five for right. Okay, this doesn't necessarily mean the problem is upstream of this due to all the feedback stuff. However, I can go to the output of the first stage filter. So left is on pin 14, three, four, five, three, four, five, six, seven, so 14 is this one. That doesn't look like an audio signal. And on the left channel, that's pin nine, seven, eight, nine. It's not what I expect. This is the side that I know works. There's the output of the final stage at seven, eight. Interesting, nine. So how is this possibly working? Pin eight, pin nine. So where is this sine wave coming from? Okay, this is connected to pin 33 of the polar, which I believe pin 34 is this one. That's showing our square wave. And I can toggle the music around. So that's actually showing music back to the square wave. So pin 33 should be there next to it. Interesting. So we're getting nothing out of the right hand polar channel. But so here's the sine wave that's coming out of the op amp on pin eight. That's the first stage of the right hand channel. So if I turn off the left channel, now turn off the right channel. Okay, I'm pressing keys on the keyboard. It's not quite in view. So on, off. That is showing, I'm getting a signal out. So what's happening over here on the polar pin? Nothing. Okay, pin nine. Toggling, nothing. So pin 10 is a voltage bias. That looks more or less right. I'm confused. There is nowhere else the audio can be coming from. So pin eight is where we're seeing our sine wave. And we know that this is actually like the audio signal because like there is music, there is our sine wave, there is the higher frequency sine wave. Well, I am thoroughly confused. I can find no way for the signal to be going from the polar over here to the op amp here. But the signal is still coming out of the op amp. So the only thing I can think of is that somehow my Amiga is haunted. So what I'm going to do is I am going to again take this op amp off the board. Then I'm going to fire the computer up because this will disconnect nearly all the filter circuitry. And then I should get a more accurate view of what's coming out here because then I won't have the actual components of the op amp interfering with the signals in these pins. Good news is at least I'm going to be getting a lot of practice with my surface mount stuff. Okay, so we can probe pins 8, 9 and 10, which is the first right op amp. And we can see there is a signal coming in and it's not a sine curve anymore. Presumably because this is now not connected to most of the filtering. And there is our input pin, pin 9, exactly as expected. And the schematic says that this is connected to pin 33, which is this one, but there's no signal there. So where is this connected? We want this pad here. And this is the one it should be connected to. Interesting. Sure, I checked that pin. But let's power it up again and try that again. Okay, so this all sounds like a mistake due to me having the pin out here incorrect. But let's fire this up. So there's our input pin, turn on the music, turn it to the sine wave, there. Okay, there is our signal and there's the other channel. Oh boy, so it's not these two pins, it's these two pins. All right, well, you know what this means? It's time to put the op-amp back on again. Okay, let's try this again, shall we? So, signal, music, sine wave, nice sine wave. Okay, and now we're here. We have, wait, what, what, what? So coming out to the polar, we have a sine wave here, nothing here, nothing here. But we now don't get any distortion. So pin one is the left channel and pin seven is the right channel. Oh sorry, focus, focus. There we go. Pin one, pin seven. This looks fine. So let's just, so we can turn this one on off and we can turn this one on and off and we can toggle the filter. It doesn't make much difference because this is a pure sine wave and we get signal here. Oh, hang on, it's all turned off now. Let's put that back on. Okay, get signal there and there. So for the, yeah, pin seven and one are the outputs. So this, I believe, to be working. Well, I have the, I have channel four of the oscilloscope still hooked up to the red channels. Let's turn that back on. Okay, and let's remove this probe and put back the other channel. Okay, we make that match. So we see here 1.4 volts for purple, which is the yellow channel. We go to blue and do the same thing, 1.4 volts. This looks like it's working, but we still weren't getting any signal from over here. So now, now the ghosts appear to be passing the signal from both polar channels to the op-amp. I can see a little flake of goop here. That was just fluff, not conductive. I have no idea what's going on, but it does look like it's working now. I don't know why the probe, the oscilloscope probe, wasn't seeing anything come out of here. This is extremely peculiar. Okay, well, let's hook up the headphones and see what happens. According to my VA meter, those appear to be the same volume. Let's just try the music. So I think that's working now, which is very, very strange. So I think what I need to do next is to rig up direct capture and get some high quality audio of what this is actually all supposed to sound like. Putting it back in the box might help too. Look, it works. Well, listen, really. So getting the lid on was more annoying than I thought. I thought for a horrible moment that one of the through-hole capacitors I'd bodged in was rubbing against the bottom of the disk drive, but it turns out there was just one of the toggles on the RF shield that I'd forgotten to bend back down again. But it is now all together and everything still seems to work, which is nice. I will switch it to the sine wave and pan left and back to the center again. It's possible the timbre is a little bit different from the left and right, but this is good enough for me. I can't really tell for sure whether it's different. I've looked in the oscilloscope and it all seems to be fine. So I'm going to call this done. Also, I found out why I was getting such weird results out of the polar by didn't have actually going and asking someone who knew. So the audio comes out of the polar through these two wires here and goes into the left and right filter set. Now, when I connected the oscilloscope up to this end of these wires, I was getting nothing, which is really weird because, you know, I'd expect C audio coming out. But if I connected it to this end of the same wire, I was seeing a signal. I now know why it does this. The polar emits a constant of voltage output where the current varies to carry the signal. And the oscilloscope only registers voltage. This is weird. I've heard of current signaling, but I thought they went out of fashion in the 1950s. So when the oscilloscope was hooked up on this side, the voltage was constant. So I saw no signal. When it was hooked up to this side, because of the resistance of this wire, there was a voltage drop and the voltage drop would vary depending on the current, thus producing a signal which the oscilloscope sees. So this is all kind of strange, but at least there is a actual explanation as to what I was seeing, which is very nice. So let me just pop the disc and reboot the thing into workbench. I can see the hard drive lights here. On, there we go. So in here, here, here. It's showing nothing because for some reason the Xenon 2 files are not icons and I haven't figured out how to fix that yet. Run this, do this and that is the Xenon 2 music, the way it is supposed to be heard. So that's great. This project actually in real life has taken weeks, mostly due to having to get the op amps delivered. So I'm really glad that's done because I've got other stuff I want to use the workbench for. So until next time, I hope you've enjoyed this video. Please let me know what you think in the comments and I'll just let the demo play out.