Hi, it's repair time or at least attempted repair time. This one comes from the Eev blog lab. This one I've had sitting around forever. The Keysight Dso X 1102 G None of that uh, black case rubbish that they've got these days.

This is a good old beige box and a hundred meg two gig sample per second jobby. Very nice scope of course, but uh yeah, this one is as it says, on the top. rooted as we say here in Australia And don't know when I put that sticker on, but it was at least a couple of years ago when I powered it on. It came up with a uh, uncalibrated error and if I remember correctly, um, yeah, what? I think one of the channels.

I don't think it was both. Hopefully it's only one of the channels because when you've got when you're repairing a product and you've got something like in this oscilloscope that has two identical channels, you want to hope that only one of them failed because then, um, you know you've got another channel that you can physically probe Comparison to. There it is. System concerns: detected instrument is uncalibrated whether or not it lost its calibration, and that's potentially another fault or whether or not most likely it's related to the uh, vertical problem.

Now I believe I first encountered this when I was using this Um to shoot a video and I was measuring some stuff and it just didn't seem right. The values seemed out, I think, just didn't make sense. So I yeah, I finally came to the conclusion that uh yeah, it was rooted. So um yeah aside, it went.

and I haven't had a look at this since. So let's give it a bow. and thankfully it's got its own test generator build here. We can just hook that up to here and see we don't need any external stuff.

So let's go. I don't have the license code. Oh bummer. Thankfully we have a backup.

We've got our probe calibration signal and yeah, we're getting something. No workers. Let's uh, let's trigger on that. Shall we? Trigger Type Auto sauce? There's your problem.

Source: Number one. There you go. Like a bought one. Anyway, we could tweak that with the pot there, of course.

but anyway, that seems to work. So one Kilohertz, that's what you'd expect. I don't know what the signal level you'd expect, but uh, let's compare it to Channel Two. Now that looks right.

Uh, 500 millivolts per division. 50 millivolts per division. One of them is obviously set up for. uh, ten.

One to one. there. This one will be set up for tender one. There it is.

So if we turn that back, no wackers. and uh. 50 millivolts per division. Now it's making a it's making a fool out of me.

Um, it works. Oh yeah. look look look look look look. there's your ground reference.

Shift it Whoa. Look at that. It's shifted down. That's right.

I remember now. Yeah, it wasn't the It's not like the signal failed. Yeah, it's all coming back to me. Yeah, look the D Yeah, look at that.

the Dc shifter. We're in Dc mode, right? We're in Dc coupling and Dc coupling. And all of a sudden, Yeah, look. it's gone negative.

So there's something wrong with the Dc offset. So yeah, if I put both to the same level there, I can cheat here and just set it to uh. line, uh triggering. so we can at least see the waveform.

And then we can swap between the two channels. right? Yeah, Well, yeah, look yeah. Look the Dc offset. I didn't even notice that.

Yep, Yep. So we've got actually got a Dc offset problem on both channels. so the sampling seems to work, the Adc is working, the triggering system's working The you know, everything seems to be working, but we have a Dc offset issue on both channels that's annoying. Um, so there's probably something common.

Um, that's weird because I would have expected the Dc offset to be generated when you, uh, you know, turn your vertical position control. here. It adds a Dc offset value to the signal being measured, and I thought that would have been generated within the channel itself. So oh, we just saw a reversal direction there.

So slight drift between the 50 Hertz mains and the one Kilohertz internal. It's going to go back. It's going to drift back. Oh lovely.

Anyway, that's fascinating. I've done a video on clock drift Actually, I might have to link it in up here if you haven't seen it. So yeah, that's a bit of a bummer. Um, I would have liked to have had like one functional channel.

So yeah, I wouldn't have expected the Dc to be central, but it could just be like a power supply power in both of them or something like that. Because I know I remember from the tear down, there are, and as you'd expect, like some local regulators surrounding the input. uh, circuitry. So hey, what's oh no, that's just pick up from here.

Yeah, something just switched on. I've done a video on common mode rejection pickup as well. Hmm. Anyway, let's crack it open and just to show you what it's supposed to do, of course, here's the black version.

The black version works. The beige is the problem. There you go, fixed. all you do is spray paint it black.

Um, yeah. there you go. So there's no change in the Dc offset and the calibration output is a Dc reference. So yeah, something weird happening with the rooted unit where it's uh, based on the range like has Dc offset issues.

Which is interesting because I mentioned before, like the external voltage regulator like, you know, powering. uh that if if that was a problem, then you'd expect it to be a problem on all ranges. possibly. So yeah, this is.

this is a weird one. Guess which unit this is anyone remember? Um, trust me, that's not a factory. Those trim pots aren't factory fitted. Oh, this is my original hack hacker unit.

I did that video hacking this scope. So oh goodness yeah, I've I've screwed the pooch. Who knows what I've done to this thing. Um, the poor bastard.

There's probably I'm gonna say right now there's like nothing wrong with that front end. I'm gonna say I've done something horribly wrong to the scope. So the first thing I'm going to have to go do is watch my video where I added these trim pots. where.

um, if memory serves me correctly. When it boots up, it reads a voltage divider and that tells it what bandwidth of the scope it is and stuff. But I like, I don't remember that ever screwing up. the.

I left some screws out here too. Look, that's a bit how you're doing. whoops. So yeah, I don't recall there ever been any issues with it I can't remember.

Anyway, adult, this is my hack scope. Yeah, so this is not a keysight failed instrument. This is, uh, a day of fail. Um, yeah, I've done something horribly naughty to this.

Okay, after that embarrassing revelation. Uh, don't hack your products kitties, You're gonna come And guts are like Uncle Dave. Um, anyway, because it seems to be like a a calibration issue, It says it's uncalibrated and of course Dc offset would actually is part of the calibration. I think you can do an auto calibration for Dc offset.

So why it's actually lost this calibration? I don't know because I remember at the time the hacked scope was working. So yeah. anyway, like maybe I around. I think I vague recollection of around with it.

more. Perhaps after the um, yes, I checked two videos that I did on this thing. Um, so maybe we can go into utility and service and start use a cow, shall we? Well, no. let's do hardware, self-test Let's see what pops up.

Nope, There were self-test failed, trig comp and max. Oh no, that's not good. There's more to this than it. Perhaps it wasn't my hack, although most likely it's something to do with it.

but you know it's self-test Failed it. trig compensation I presume and and marks yeah, what's going on? Um, it is the one mega zoom for Asic, so it does mux between. No, no, does this much between the channels I can't remember. Um, Anyway, I don't know what mucks they're talking about there, but that's interesting that those self-tests failed and not this.

Anyway, let's um, run a starter user cow, shall we? So we'll give that a bowl. Calibration factors are protected. Go to utilities option. Oh god, we've got a cow protector disabled.

See. I would never have disabled the uh protection on this thing. So anyway, let me go disable that. Utility options auxiliary Cal protect Disable that back back utility service disconnect all inputs from The front panel before uh, using hardware cal or use right start.

User: Cow. Okay, oh, seven minutes, I will get back to you. Yeah, all right. and the good thing about this is you can actually operate this.

uh with the case actually off you can probe as I saw in the uh, hacked videos linked up here. Um, because they're rather fascinating. They're 40 minutes long, so I haven't watched the whole damn thing again because that bloody Eev blog guy likes to bloody waffle on. Geez, You know.

Anyway, you can see. look, it's uh, shifting the Dc offset there. Um, so it's it's doing that for each channel, so it's going to be interesting to see what comes back at the end of this. I don't know.

You know what these waveforms are or whatever, but it's obviously generating those internally and using those seems like an oddball waveform to use for calibration, doesn't it? Um, yeah, I don't. I'm not really concerned with like doing this calibration with the back off and stuff like that. It doesn't really matter like it's the front end cans or there's still shield and stuff like that, so no worries. So after all that, we got the super useful message user Cal failed.

Okay, well, thanks for that and you can see that the Dc offset is way below where it should be. unless you go to 200 millivolts. Oh one volt, it'd suddenly jump back down to oh, look, yeah, see how it goes? Like one two five gets towards it and Ten is perfect. I guess the only thing left to do really is, uh, restore this thing physically uh to what I had before.

So like I could go and watch my own bloody videos and work out where the, what, the voltage, uh, reference points were and to set the trim pots and everything back to where I'm better off trying to just know, physically removing the entire hack, putting back the resistors. If I've still got the values, I think I'll try and just physically restore it. First things first, and get back to where it originally was. I might have to crack out the uart too.

Yeah, it looks like I've removed all four of the resistors there and replaced them with the trim pot. There were two separate voltage dividers there, and uh, two trim pots. So yeah, I don't have the original resistors, so hopefully somewhere in my video I've got the original values. Now, as it turns out, these resistors in here that I took off going up to the trimmers up here we actually have in the original video here it is the Eia codes for these and yeah, sure enough, we've got uh, two 10k resistors in there as a voltage divider to give mid rail which is 1.25 volts and the other one um to give 0.69 volts.

So yeah, we've got the exact values they actually were marked on the top, whereas the ones on the processor board aren't But we've got the voltages for those two. Of course, I don't have any Bloody 4k Sevens, do I 470? Ohm, 470k. Um. Bloody Murphy.

Aha, we might be getting somewhere. I, uh, replaced those resistors on the main board. Haven't actually measured the Uh voltages yet. Values are supposed to be 12.1 K and 4.6 4k, but a 12k but an E12 series instead of the E96, the 12k and the standard 4.7 K and that gives you know 0.7 instead of 0.69 volts.

So it's going to be good enough for Australia. and look, um, it's obviously um, detected that change because we never had this on boot up before. System clock is defaulted, instrument is uncalibrated. The default setup was loaded, so that's promising.

So may you know, Maybe this could be as simple as I was simply tweaking fiddling with don't twiddle with your knobs. Let me tell you. um, I was. I was fiddling with my, uh, trim pots and um, maybe I could just completely and utterly screwed it up and put it into some mode that it didn't like and that, just like I don't know, corrupted the default boot up and maybe the calibration.

although it shouldn't, But you know you never know you're lucky in the big city. So yeah, I'm going to run through, uh, the system check again. but uh, before I do that, look, look at this. Look at this.

look at this. Ah yeah, yeah, there's no Dc offset. Let me plug the probe back in. Is that all it was? Is it did that? Yeah, it twiddled the uh.

trim pots. Hang on. All right. there's our signal.

and sure enough, that looks good. I mean, yeah, I'm sure it's probably lost its calibration values, but I don't know. Maybe I don't know how we fixed that because I don't think there's any like user calibration. At least the data is not available for it.

But you know. Anyway, we can now check exact signal levels before, but our Dc offset issue is gone and I guarantee you it's gone. Ski on Channel two as well. I don't even have to trigger off that to know.

Yep, yeah, we fixed our Dc offset issue, so that is fascinating. Just trimming the pots. And remember, we've got two different types of pots in there. We've got four pots in this thing.

two different types. One is the product configuration, which was the ones I just changed. They're on the main board. There's two voltage dividers on there, two different voltages which give you uh.

here's the screenshot of the original Uh data dump for it. And then we've got the Blt ones. Blt of course, in Australia is a bacon, lettuce, tomato sanga and those Blt trim pots. They uh, change the module uh configuration.

So and and I haven't fixed those yet, they're still the original trim pots at whatever values I left them at. I couldn't be bothered hooking up the uart yet, but yeah, if I just put in the default resistor values from before. But anyway, it seems to have come good. But anyway, changing those product configuration bits, you? so with those, there's only two bits on the product configuration.

But because we're talking about multi-level Adc reading, you can have as many levels as you want. I think there might have been four levels from memory per bit, so that gives you a fair number of configurations. Anyway, there are configurations where you can completely come agata and it just doesn't do the Dc offset properly. Um, so yeah, it was.

It was those two trim pots on the main board that I was obviously around with, but I swear I would have had this working when I put it back together and closed the case. and I swear I had used the thing. Now, possibly I could. The only thing I can think of here is that I might have been the trim pop might have been right on the noise margin, right? Or if you know, just being between one mode and another mode and I thought, yeah, no worries, I'm in the middle.

I obviously didn't hold my tongue at the correct angle and um, I think it's just slowly drifted into over time. Um, or you know, just like different temperature or whatever it is. You know the moon's not the right phase at the moment and it's changed product configurations and that's just completely screwed around with it. There you go.

That's a repair of my own goof. Fantastic. Okay, I'm going to start a user calibration again. Hey look, I've got my wavegen output back.

Did those? Did that product configuration disable the wavegen? Oh boy. Hang on. Um. Anyway, I'm going to disable Cal Protect and I'm going to go into my wavegen.

I got it. I got my wavegen's back so it looks like the product configuration can override the license in the thing. So it obviously had the license in there. But if it didn't have the Pr product configuration, it goes well.

I, physically it goes. I don't care, there's a license installed. You don't have a hardware Sig Gen installed in this thing. But do they sell this without the hardware? See Jen.

I can't actually remember. Yes, Yes, I think they might. So there you go. I think that's some something that we didn't know before from that original hacking video.

So I we've learned something new. This video wasn't completely worthless. Anyway, I'm going to go in there and start that user calibration. No walkers.

We'll come back in seven minutes. Waveforms? Yeah, the same as last time. Yeah. so they've got all sorts of cruddy things.

Yeah, look, it's all over the shop. Anyway, Come back to seven minutes. I reckon it's going to work well. Actually, I hope it doesn't because then we'll actually have something some hardware fault to actually troubleshoot rather than just fixing a stupid Dave goof use a cow past win a winner chicken dinner.

There you go. We can get to a point where you have got an invalid product configuration and it won't pass user calibration. You would have thought that, well, you wouldn't allow that right? I don't know. just in case.

Like from a programming point of view, I don't know. Programmers out there tell me, Is this like a a, uh, lapse in um and a bit of an oversight here or is this oh well, No, of course you know, dick around with the hardware. You get what you get and you don't get upset. But I would have thought that like any product configuration should, not be able to screw up the calibration and the Dc offset and things like that.

I mean I I don't even know how that happens. Sure, you'd have a robust enough system so that well if you did get into the wrong mode for insert reason here like you have a user who's around but trying to hack the thing, uh then yeah it screws up the Dcos and looks like for all the world like a hardware fire. Like I thought this was a hardware fire and like my mind instantly went into hardware mode and it well it's well technically was hardware but not in the way that you'd expect. like user calibration and and you know, Dc offset and you know, adjustments between vertical levels that should have nothing to do with the product configuration.

So anyway, yeah, I don't know. programmers out there. let us know what you think. Have you been involved with something like this before where you've dotted all your eyes and crossed all your T's so that no matter what the users do, they can't possibly.

um, you know, screw it up in this way. But yeah, trust me to do it. And it seems to be bang on calibration. I'm feeding the Sig Gen out, which I've set to 500 millivolts.

uh, peak to peak here. And um, you can see I'm reading 508. so that's that's not too shabby at all. Is it? So I can measure each range? 3 10 315.

Like, you know that's good enough. Like scopes are not that accurate. They're only like, you know they're three to five percent accurate or something like that. Like, a really good scope will be like two percent accurate or something.

So yeah, then they're not that great. So let's change the range again. 3 10 We're measuring 315, no Workers 120, Measure 121. Go back down even more.

Bring it up to near full scale. When you're testing calibration like this, you want to do go near full scale 344. We're getting down into small signal levels now. So 130.

So yes, I know that the calibration could have screwed up the wavegen as well, but it's unlikely that both of them out by the same amount so I can double check with another Uh scope or another function. Gen? of course. No, I'm I'm fairly confident that this is actually okay. Yep, 70 millivolts, no workers, even down to the smaller signal levels 9.6 We're measuring 9.8 no workers.

and that's one millivolt per division. Which isn't true. one millivolt per division because this scope is and this is only now we're getting into the digital stuff, but 6.7 I'm measuring 6.8 Let's go up to 12 volts peak to peak. Yep, 12.1 Yeah, that's a winner.

So that's kind of disappointing. Actually, I'm gonna have to go through and fix up the other resistors the bacon, lettuce, tomato resistors in there, and put those back to their original values. But yeah, it looks like it was the product configuration that was screwing it up. which kind of makes sense because the other ones were just like uh, modes or something.

I don't think I ever I can't recall details of and followed uh through some other people. uh, took the reverse engine in further that I did in those two videos and discovered all sorts of stuff. but I would um change those back. But yeah, it's the product configuration that we came a gutser on here.

Oh well, what would I have done next? Uh, I would have got in there checked any voltage regulators of course. First rule troubleshooting. Thou shall measure voltages So I would have uh, looked for any little sot 223 regulator looking package either for the main one for the whole board or as I said, I believe there's some local regulation around there is there? Let's have a look. Yeah, I'm not sure if there would have been any voltage regulation in there or in the can.

we'd have to take it off. uh, but there doesn't seem to be any like that over there. that could be a voltage regulator for example that. but that's more got to do with the Uh trigger system which by the way, the Uh trigger system on the scope.

you can actually use it like as a third uh channel. They don't advertise it very well, but it like it's digital only doesn't have the full analog front end, but you can actually display the signal. You know you used to be able to get this back in the old day. I had an analog scope.

uh, what was the Cos 6200 and it was a 12 channel scope or was it 14 channels? Yes, I kid you not, it's because you could get um, it was a four channel scope but then you could also get the trigger view as well. This is what it was called on analog scopes. uh, trigger view. And then you could also double those number of waveforms because you could get the displayed sweep waveforms as well.

And then and then it had an extra channel somewhere. I thought it was. I think it was at least 12 channels. anyway.

The Cos 6200 I believe it was. jeez. why why'd I ever sell that? That was great scope. Anyway, yeah I would have measured all voltages.

I would have certainly checked because when you dick around and solder and hack things like this, I would go in there and visually inspect. check for any like little solder balls because when you're soldering on a product. bit of a pro tip here. Um, you can often get like you know it can.

The solder can spit, give little uh you know splashes and you may not see this at the time you're doing it and it may uh, leave a solder bore or a solder slash somewhere which can then flap around in the breeze and move around in your product. or you know, and short between pins or something like that. So you give the board a good visual inspection. then you might give the board a good clean as well.

If you've you know been hacking around on it. once you restore it to its configuration or you do do your repair, you want to get in there with a hard bristle brush and give it a good wipe with your uh, isopropyl or whatever it is. Uh, you use. um so yeah.

I would have got in there and measured voltages, visual, have a good tidy up, and um, yeah, then well. I don't know if it still wouldn't have worked after that. I don't know what if what I would have done because we can't get the schematics for this thing and it happened on both channels and well, it's not actually a real hardware fault. it seems to be just like a software induced fault, so that's weird.

Anyway, that is fascinating. Um, not entirely pointless video, but yeah, a bit embarrassing. but I always post my embarrassing, I don't care anyway. hopefully you learned something.

So anyway, if you liked it, please give it a big thumbs up. And as always comment down below: catch you next time you.