DR #13 - Tektronix 2213A Oscilloscope Troubleshooting and Repair Part 2

all right so I got tired of waiting for that part the attenuator from Greece so I wised up and I did what I should have done before I even ordered the part and I pulled the attenuator out of the channel one so you can see it's out of here and I swapped it with channel 2 so here they are out of the board here and it was a lot easier than I thought it would be because they're not solder they're actually socketed so these are these are all sockets here and I wish I would've known that I would have swapped it before I even order the part but swapping them did nothing channel 1 still has the issue and channel 2 still looks good so it's not the attenuator I'm glad I checked because I would have waited the 1 to 2 to 3 weeks for that attenuator to come in only to find out that it wouldn't fix the issue so so I did some more digging I went back to the schematic and again the two areas of concern were that pin 5 and pin 8 that's what they call them it still looks like pin 1 and or excuse me pin 6 and pin 9 to me but then as I discussed earlier there certainly isn't anything at least on this schematic other than this 10x attenuator so I thought that should be the issue so I looked at the board a little bit closer and I realized that the board and this schematic don't match up completely so I don't remember if I mentioned it earlier but this schematic is actually a 22 15a and again I am working on the 20 to 13 a the reason I have this schematic is because the 20 to 13 a schematic does not exist or I can't find it I did have the 20 to 13 schematic but that attenuator board is completely different and so after looking online I was told that the 20 to 15 a has very similar if not identical schematics other than a few minor differences this must be one of the differences so I'm no longer gonna trust the schematic and I did some poking around on the board and so first of all on the schematic it doesn't show you any of these components here so pin pin 8 or pin 9 you know they call it pin 8 in this schematic I think it's the ninth pin comes to this resistor here zoom in here so comes to this resistor it's also you'll see it hits this capacitor here and there's another resistor right here it's tough to see and then it comes to this resistor through this resistor there's another just right here that's tough to see and then comes here into the middle which actually leads to another resistor on the back of the board and then this is part of our attenuator so anyway I checked all these resistors they're just fine they also match up with channel twos resistors as well so I did the they're all in a series I measure the resistance they all look to be fine the capacitor seems to be fine I highly doubt that fail and so I did a little more continuity checking I said earlier that I don't think it's a connection issue but after digging some more I've changed my mind so let me get the light here it's a little better ok I'm gonna remember what I was looking at some papers so let's see I'm in the correct range right now so you can see pan of interest right here is this one so the one directly behind this capacitor so you can see there's two pins on this little fork here and there you can't see it but behind here they're actually attached so they're continuous and you can tell when I put them together obviously you can't see what I'm probing but this is this is a continuous fork here so these two pins they look separate here but they're actually continuous so the pin on the right of this fork leads to this this the capacitor this resistor and this resistor is aligned and series here so I check continuity there and it's there but when I check from the other leg so the left pin of that fork over here I get no continuity okay and I'm on that pin and so if we move up to channel two I do the same thing in the same position just to verify so again I'm on going from the left pin to the right pin you see we have continuity and so what this means is you can't tell what I'm doing but I think now I've definitely found the issue and you're not really gonna be able to see it so I'll just describe it this right pin here on the fork I'm gonna put my probe ever so gently on there and then measure to this resistor again this should make contact and it's not now if I push down on this pin you can hear the contact if I release it you can hear there's no contact so if I put a little bit more pressure on there there is continuity so the issue is that pin is not making complete contact with the board and so that's what's causing our issue so the question is what's the best way to fix that I mean to do it a hundred percent right would be to pull this attenuator board out again which means you know disassembling it's not too big of a deal I did that and then pulling this whole switch rotor should rotor switch off to gain access to all these pins and then probably just bending that pin in place but I'm gonna attempt to bypass that and just try and Bend this pin ever so slightly so that's making good contact it may work if it doesn't I'll pull the board out I'll be back either way and let you know what I found I attempted to bend the fork while the switch was still installed in the board it didn't work I broke one of the tongs off one of the pins off so I pulled the switch out it was actually easier than I thought I wish I would have done it at the beginning it's just in this little modular fashion here and there's just actually two screws on the bottom and it pulls right out so I wish it would have done that originally so as I said I broke one of the tongs off I was able to get this fixed I got very very lucky so what I did you can see this middle pin here with the the solder so it's not the prettiest thing but I'm gonna leave it because this is the only way it's gonna work and if I try and make clean this up and make it look even better I'm I know I'm gonna screw it up again so I got very lucky in that two of these pins you can see all these little tongs here there's actually two sets and they overlap you know and there look see you on top of each other they they overlap right and I looked at compared with the other switch and if you see the two prongs on the right as I go the entire length of the dial they never make contact with the board they're always in the raised position and actually this this switch has been used so must be used on another maybe another model type or something like that the third pin over there is always making contact and the two on the right are never making contact so the two on the right aren't used so what I did was I clipped both of them off and I needed both of them because I I melted the first one so if you look closely at these you can see it's just one metal strip with the you know metal strip coming out of each but then you have these little tongs coming out and they're attached with this little piece of plastic and so trying to what I did was I cut one of these off I attempted to solder it on here and hold it on there too long and this plastic starts to note that's exactly what happened on the first one so I got a little too ambitious the second one I got lucky and it stayed I think it looks pretty good it's not perfect but it's definitely on there I think the distance is right and I think this is gonna work so it's hard to tell if it's bent into place right now I kind of bent it down just to make sure there's gonna be enough tension so I'll reinstall it and we'll see if it works after removing that strip I don't know five six seven times to try and Bend those pins into place I finally came up with the solution which was to add a little bit of solder to the pads and that worked like a charm so I have the board reinstalled and everything I believe is connected up correctly everything's turning nicely and we're ready to test it out so here we go all right and plugged in cue the magic smoke in three two one all right fire it up a lot of noise there that doesn't look good that's not a good start is it yeah it's not a good start that could be the solder job on the resistor so there's a resistor between this the input pin and the actual attenuator board and every time I remove that board I had to desolder and then upon install resolder and that thing got pretty worn so maybe that has something to do with it but let's see if we have a signal anyway so we're in the one we got nothing that's no good forgot something here oh no it's even worse even worse [Music] and I don't have a signal at all anywhere it's just super noisy you can see that something's not right there figured out why I wasn't getting any signal on channel 1 and my previous assessment that the two pins on the right here were unused was incorrect so it is true that the volts per division knob does not couple to this rotor here couples to this rotor but what does couple to this is the DC coupling knob and so there's three set points there right ground AC and DC coupling and so all three of these pins are used one set for each you know so you can see on channel 2 the left most pin is down and enabled that's the one that I have so that's why I assumed the other two aren't used but this is in the ground mode so what I did basically was I removed any chance of DC or AC coupling so you can see if I get started to move it like should be able to move it by hand it's hard for you to see there but didn't there we go now the leftmost pin is up and the two on the right er down and that I believe is the AC coupling and then you go one further the other way you get DC coupling but anyway that's the problem so what do I have to do I mean I I was out of luck anyway because I I didn't have one of these pins so I had to do what I could to try and get it fixed but I I do need the entire strip here so yeah there's two strips overlapping here and I do need I do need every pin on each strip so how do I fix that well I cut these back as you can probably see can see I cut the two pins back right here right here I cut them basically all the way back to the base of the strip so it's gonna be pretty tough to tie anything on to there to make a new strip and to make it work it's not gonna work so I looked online and I found this exact board well I should say it's not this exact board it's a yeah part number here right up here six seven zero eight two six seven - zero - I found a 0 - 2 0 1 and that's for a 20 - 30 to model something like that 22 33 this is the 20 to 13 it looks identical obviously there could be some differences component wise but all I had to do was match these up all of these nodes here on both rotor shafts match up identically so I'm very confident that the strips are gonna be identical and so with that board I'll have four spare strips I only need one but before I go ahead and buy that it's it's not too expensive so just the board it's definitely worth buying that if I don't have any other problems with this let's go so what I'm going to do first is verify that I fixed the original issue of basically no signal on the 0.5 0.2 and 0.1 volts per division to verify fix that I'm gonna swap the strips between these two so that this is making good contact over here and then we'll check out the signal on channel 1 if it looks good I'm gonna buy this borgin and then we should be all good so I'll swap the strip's and I'll be back all right strips are swapped channel twos strips up here as you can see by the missing pins here and the amended pin there and then the nice clean strips here now on channel one okay we're all swapped ready to reinstall and test I installed the board I'm not even gonna bother putting channel twos knob in there because I'm just gonna have to remove the board anyway when I get the the new strips in but I wanted to test channel 1 to make sure a that we have a signal back and B that we resolved the original issue of no signal on point five point two point one volts per division so here we go I'm on channel one I'm at one volt and we still have our signal there good so we resolved that issue now here's the moment of truth is it gonna work in this range starting at point five yes got it point two got it point one alright that's good news so we resolve the original issue again that was the the fork on the strip not making good contact I think it was number six so I just added added a little solder to the to the board there so that it would be raised and then make the make it easier for the fork to make contact so that's good I'm definitely an order that board I'll replace the strip's on channel two and we'll test it them but everything's looking good so far pretty excited I finally got the new board in from grease and it looks nearly identical to the old board I'm very confident that the strip's are gonna be the same so I'm gonna go ahead and remove these strips and I'll just replace both sets while I'm at it I'll also remove the solder that added to these solder pads here I shouldn't need that at all the new strips should be able to take care of it and we'll see where we're at after that I'll be back after I reinstall it all right moment of truth time to turn it on and see if we resolve our issue I'll start with channel one and there's a signal I'm at 5 volts per division didn't have an issue here before let's make sure we still don't know it's still there let's go to 2 volts per division still there 1 volt looks nice half a volt still looks nice good so this is where we had our initial issue and we have it turn that down a little bit so you can see it better let's put a point 2 volts per division still looks good in point 1 good so that scale is it's good and we're all the way we're good all the way through excellent let's try point to our excuse me channel 2 I did swap the strip from channel 1 channel 2 and then we had our issue on channel 2 so let's make sure that that's resolved now yeah we'll start off at 0.5 or 5 volts per division good still there and twos good and ones good and good 0.5 looks really nice point 2 looks really nice point 1 looks very nice good yeah we keep going yeah it's all the way there good it's bright awesome so that's fixed I'll probably do a little bit of tweaking feel if you noticed on channel one judicial spike up front half that waveform you can see that a little bit of overshoot on up-and-down so that that may be a little bit of tweaking you know I did mess with a lot of the potentiometers on that board so I may have to go through the service manual and make some adjustments to those again to make sure that that overshoot is gone thought I'd show you I just went off a hunch that the two potentiometers that I was adjusting on the actually are two capacitors on the attenuator that I originally replaced I just started on one of those and swatch that overshoot goes away so here we go it's not looks really good now I'll throw a sine wave on there maybe a 5 kilohertz and we'll see how it looks alright I cleaned the scope up really well cleaned up nicely actually was able to get most of the gunk off the stickers there was a big yellow swatch up there that I was able to remove for the most part and I have them hooked up to a rolling audio signal so it's gonna it's gonna change from 20 Hertz to 20 kilohertz I thought they'd be kind of interesting to watch they both look really clean I'm sure it'll have trouble triggering at some point based on the time scale so I'll have to adjust that but we're at 4 kilohertz right now it's looking pretty good change that you can see it it's always shifting but it's looking really good I'm very happy with it everything seems to be working really well so I'm going to call this one fixed and I'll just let this one play out up to 20 kilohertz we'll see if it'll make it I'll have to increase the I'm still going see the amplitude is decreasing as well and it made it to 20 kilohertz look pretty good alright that's it another scope fixed I got another one coming the TDS for 20k I believe they won't paw around so I'm excited to start working on that it should be in this week so stay tuned for that and thanks for watching we'll see in the next month you