Hi welcome to another repair video for this classic. HP 35670 Dynamic Signal Analyzer. And if you haven't seen part one of this video, I'll link it in down below. Yes, this is part two in a series.

Maybe depends how long it takes me to fix this thing, repairing this unit, or attempting to repair to attempting to repair because we don't know if it's uh, you know whether or not it's beyond economical repair or whether not. Um, it's it's going to just require another 5 minute video. um to fix I have no idea but I had a lot of people comment on it. Can I do extra videos? Uh, fixing this thing? And yes, that was my intention to do videos until it's repaired Or until I decide? Eh, it's just not worth the effort.

So here we go: Um, I'm going to have another look at it. another crack at it. Now to recap: uh, what happened last time? We have a no and faulty power supply which presumably took out out. well, best guess took out a 7912 -12v regulator on the digital board and that stopped the oscillator working.

So we have got to the point where the unit does actually power up and uh, runs through the software so all the digital part of it working fine. But we were getting uh, error messages on there saying that the ADC Asic has failed and uh, a lot of people said well, let's go push the ADC Asic back into the socket and all that sort of thing. No, I don't think that's going to be the case or it could be But I think the most probable scenario of what else is wrong with this thing is, well, more power supply stuff because we've had a no and fault in the power supply and at least one failed voltage regulator. Usually they're pretty reliable and usually the fure mode is uh a you know a high voltage on the input which could be caused by a failed Mains power supply which we know we have.

these are no and fault. So rather than chase our tail Chase red herrings and follow the service manual for the rest of this thing, that whole 70 page troubleshooting guide for this thing, you got to take a step back, think about this and go. well. what's most likely to be wrong with this thing? Is it Actually the software tells us there's a fault with the ADC as but hey, uh, you know if there's no power going to the ADC ASC then you're probably going to get exactly the same error message.

so it's I reckon I would. Well where I would put my money on is that we have more failed voltage Regulators on here somewhere because uh, apart from the 5V rail on this thing which we know is good and all of our digital logic is working so it's unlikely that, uh, the failed switch mode power supply has taken out anything on the 5vt rail on any of the boards. so um, that's the only one which is powered directly from the Main's power supply. The others, uh, the this has plus - 18 volt rails and and an 8v Rail and uh, I think and a 12vt.

yeah, and a 12vt rail as well. Now the take the plusus 18 volt rails. for example, they aren't powering the opamps on all of these analog boards directly. Uh, because a design of a unit like this needs to have uh, low noise on the power supply, so it's going to locally regulate those on the other cards like this one for example, which I've just taken out.

and sure enough, T I'll show you this in closer detail, but we have some local onard regulation I'm not even looking at the Um service manual, but first portol is to measure those regulators and see if it's fail cuz if we've taken out one voltage regulator, there, a very good chance that we've taken out some others as well. So forget the service manual I smell some foldy Regulators Let's go now. of course the absolute first thing I do Golden Rule of troubleshooting Thou Shalt test voltages. So what I've done is to access all of the voltages coming out of the power supply here via this ribbon cable.

I've just taken the ribbon cable out because it's not E once it's on this motherboard, gone over this cable onto the motherboard. you know it's not real easy to probe. I Can probe the 5 volts going on to here, but how do I proe the other voltages? So I just disconnected that I have powered it up and I have measured the voltages and uh, here they are. Thankfully, the service manual provides a chart telling you what pins are what.

But basically we've got the plus 18 Vols Supply Here measured 18.3 - 18 Vol Supply -1 19.3 and you know it's a bit high, but it's neither here nor there really. Because this 18 volt rail, as I said, is probably not powering anything directly. it's just going into local uh, say 15v regulator or something like that to power the local opamps. So really 19.3 I'm not going to lose any sleep over that at all.

Not worth chasing that, there's nothing nothing doing there. Plus 12 Vol rail is 12.3 Vol the Plus 8 Vol rail is a little bit low 7.7 Vols But once again, that plus 8 volts is probably doing doing some local 5vt regulation, so plenty of margin there, you know? 2vt drop on a standard 7805 something like that and we've already measured the 5 Vols in the previous video and it's just hunky dory. So everything coming out of the main power supply here is just fine. But of course, this is the repaired power supply, so the original one likely could have.

Well, we think it's taken out that 7912 voltage regulator we had in the previous video and my guess is it's probably taken out some others as well I'd Probably surprised if it hasn't Now here's the um analog, uh processor uh board here and I haven't checked the service manual, but presumably that is the ADC Asic that they're uh, talking about there the Um actel um uh fpga there. So I believe that's what they're talking about and you can see that we have three on-card voltage Regulators there. And if we have a look here, we've got uh, some test points Min -5 Vols here. So as I said the - 18 volts.

it's uh, just regulating that down to -5 Vols we have + 15 Vols Here we have -5 Vols here and we have, well, plus 5. we don't need to measure cuz it'll be coming from the same point as no. So we've got three regulated. is there? um, uh, pairing? uh, those particular rails.

so first thing we need to do is measure those. But unfortunately the really annoying thing is is that because this is a plug-in card, I can't just uh, you know, once we slide that in there, we can't access those anymore. So uh, but thankfully it's got these nice test posts I'll just wax some alligator clips on there, have those coming out uh, just laying on top of the board. They'll be able to poke out through the side here and we'll be able to plug these those into our meters no problem at all.

Let's measure them see if they're any good actually. I Just realized that I missed one there. That's actually plus 5 Vol a for a stands for analog. The other plus 5 Vols is here and that would be coming as I said directly from the main power supply there.

but this one's a plus 5 Vols And there is the tiny 78 L5 to go along with that puppy. So I need another Probe on there? So I'm going to be probing four different voltages. All right here we go. Let's p this sucker on I've got the ribbon cable back in.

uh, ground is coming from. It's going to be one common ground for all of them. Now what I've got here is uh plus 5 Vol Analog -5 Vol + 15 Vol and - 5 Vol here. So let's do I don't know.

Let's do that. plus 5 Vols analog first. so we'll plug that in. and yeah, we're getting plus five.

So our analog, that little uh To92 package um, low power regulator was is just fine. So our analog now we've got our 15 Vols Hello! Yep. Oops, It looks like we have a shorted pass transistor. um in that uh puppy.

So it's feeding that minus 19 Vol 19.2 volts straight through to the output of the regulator. H Classic Fire Mode shorted. There you go, so you know it. It wasn't hard at all.

Um, my guess was correct. My hunch was correct. There we go. Plus 15 Vols No problems at all.

So that one hasn't been taken out. So we have an example of two negative voltage Regulators being taken out on this thing. So it looks like that one rail. So um I think this one here this.

uh, minus5 Uh, no. the minus 5 should be okay. but no, hello -5 is -1 volt. So it looks like we have now three failed negative voltage regulators.

and of course, one other thing I'm going to be looking at here. these dip Tanum caps. Um, these can fail quite easily in, um, over voltage, uh situation. So you've just got to be, uh, careful, visually, check those.

They can be really nasty, but you know visually, they look just fine. So um I think no problems there with the tanms. But you just got to keep that sort of thing in mind. And if we have a probe of this negative uh, 15v regulator here, in and out as I said shorted pass transistor.

So yep, there we go. 3 OHS between inputs and out and before I Rush down to JC Car and pick up some Regulators cuz I don't have any uh 7915 in uh, stock here. Well, let's just take a look at the Uh main analog input board and Bingo! Look, we've got some more Regulators as well. Minus 15 Vols These These aren't the same though.

These are LM 337 and LM 317. Whereas the other ones aren't the adjustable type, They're just the uh, fixed 7800 series and there's a plus 5 Vol one here as well. So I'll whack some probes on there and we'll put this card back in and just measure this board here. And we've got two other To220 packages here and here.

but they, uh, transistors. they aren't actually uh, linear regulators. and our 5V rail there is just fine. And let's have a look at this should be 15.

Vols aha -6.5 So there you go. Um yeah, that one. I don't like the look at that at all. Well, the test point is labeled 15 so it it is an Lm317.

Uh, of course, which means that the resistors could be out or it could have been trimmed to or you know, actually set to that. But yeah, I don't like it. it should be -5 It's likely the regulator's gone. and plus, well, there you go.

16 point F You Could argue that that's 16.5 They're suspiciously close to each other, so I'd say that's not a fault at all. I would say that's uh, they've been deliberately set to 16.5 even though the test points are 15, that would be my guess. and it turns out my hunch there was right on the money. cuz if I flip the board over and have a look at the resistor values here and here which set it, they're both the same uh, 237 ohms and 2.87 K and you whack that into the formula for the LM 317 and you get about 16.4 Vols.

So there you go. It's not set to 15 as it actually says on the test points there. So yeah, just got to watch out for stuff like that that could leave lead you up the Garden Path Waste time and effort. And yes, we have got a couple of these wimpy thin tab ones.

ah, cost cutting bastards. And these ones actually have a solder tab on the underneath of the heat sink there. so the heat sink? just, it's a slide on type. but then uh, secures down with a single Tab and uh, really? um, the easiest way to get these out.

If you know it's uh, damaged and you don't want to use it again, just get in there and slice the pins off and then just heat up and pull the pins out one by one. Then you don't have to worry about uh, heating up all three at once, or doing the, you know, the sideways dance, putting sideways pressure on it, and then heating up the joint. uh, bug of that and then of course, you just want to. uh Wick the holes out, apply some more uh, solder on there if you really want to.

But there we go. don't uh, pull them, don't uh, wipe them across or anything like that. There we go. Oh, almost.

That one had a bit more solder on it than we anticipated. and uh, bingo. Three nice holes. and just to check that shorted pass transistor in there, Here we go.

Hello 10 Meg Look at that. Holy crap, it's not the regulator. What do you know? H Protection Diode. Let's go to the board.

There we go. We got a crappy little like uh, you know, 4148 uh type signal diode there going between the input and output of that. So let's uh, let's measure that and see if that's the sucker that shorted out. Oh sorry, this doesn't show up very well on video, does it? No input and output.

There we go. We're still getting in a.3 Ohms, we got before, so almost certainly that diode. Well, let's hope it is all right. I've lifted one end of that diode there.

so let's measure that again and I can't see what else it would be. Yeah, Bingo look at that. No problems whatsoever. So it looks like, uh, our Main's power supply in this case I Don't know if it's taken out the regulator, it could have so you would replace the regulator as a matter.

of course. you know, considering that you've already got it out and it's you know, a dollar to whack another one in, you, just put it back in. you wouldn't bother testing it. but uh yeah.

took out that little uh uh, reverse protection Diode. There little piss an thing they put in a big 41, uh, big 41 or something. probably would have survived, but of course you have to wonder whether or not. Um, because you know we were getting uh, that 199 volts directly on that negative 15 volt Rail And it's been there for some time that we've had all this powered up and presumably when it failed as well, went through.

So hopefully, uh, we haven't uh, blown up anything on that 15 volt negative 15 volt rail attached to there. Um, it looks like the other Regulators have just gone pop. You know the past transistor bang and you know, and it's They're reasonable at actually protecting the circuitry they're powered to, but this one because it's gone to the effort to short that um, outp diet as well. Well, yeah, hopefully.

uh, not too much abuse on that uh- 15 volt rail. Well, only one way to find out. Replace it all and power it up and that is a National semiconductor. It's got 10 050 505 on it.

Eh, not your standard 1 in 914 4148 by the looks of it could be um, off hand I don't know that part number. Okay, they've all been replaced. Let's power it up. and uh, that's Theus 5 Vols that's working just fine and dandy fixed.

minus uh, plus 15 which we had no problems with before and minus 15. Brilliant. All right. I replace that D with just a one in 41, 48 should be good enough.

whatever it was, whether it was you know, signal diet or a Zena diet whatever H It's going to be good enough for a Uh to get this thing working again and there we go. Let's plug in all the cables and power thing up see if we still get that error message booting system recall State We may have to uh, run like clear the log and all that sort of stuff, but here's where it uh failed before with that ADC error. so let's see if it uh, still does calibration in progress Oh hardware error C Fault Log: Okay, well yeah. calibration fire change State yeah, blah blah blah Calibration: we'll turn that off and system utility more Fault log uh IDC I2c no device acknowledge calibration fire Okay, no more ADC fire which we'll get in before I believe Um, so that could have fixed that.

So let's now run in. Uh let's go into the um self test self test and quick Conf: let's run the quick confidence test that we did last time and uh, we got a whole bunch of failures failed one There we go. All right, we still have uh ADC Gatoray. There we go.

Looks like I think we're still going to yeah, Gatoray failed Bugger bugger I Thought that was reasonably confident we we're going to fix that by fixing our power power rails. but what? Murphy gets us again? Well the next thing I did is just take this uh board back out and just feel around the main chips to see if there's anything that's uh, you know, overheated because it's been taken out by the uh, that? uh, minus 15v? uh rail because we don't have the schematics. don't exactly know what things on here are power, but no, you know there's nothing obvious. There's a whole ton of Op amps here, which are presumably you know.

plus minus 15 volts a pop and uh, no, nothing obvious. There's a rathon chip there. Woohoo! You don't see rathon chips that often. Other thing to do is check that.

uh, we're getting and SDA there's some test points on the board and yeah, sure enough, we get something there. Let me change to another test point. should use multi Channel but uh, couldn't be bothered There we go that's looking like it's doing something and then we've got 10 mahz and uh, 20 MHz test points for the ADC and stuff. So yeah, look at that.

There we go. It's dodgy because I've got um, these Ultra long leads coming out of here and it's just oh man, just and the ground's going over to the digital board and the loop in there is absolutely ridiculous. But uh, all we're checking here is that we're actually getting a signal there. And sure enough, 20 mahz and 10 MHz cuz sometimes you're not after the signal, you don't care about the signal.

Integrity you're and that's that. Looks like 10. Yeah, 10. MHz So we're getting our data there.

Um, you know that's there's a few other test points on there I'm not sure what they do. uh, would probably have to look up the manual and troubleshooting guide for that, but it looks like it's doing stuff. and I'm not particularly encouraged by the constant overload leads on the put there that indicates uh, something? something wrong I mean these things have dedicated overload and half rail uh, circuitry in there, so to have? Oh, and we've got that sort of flashing down there periodically for the half rail. So they've got like dedicated, um, you know, uh, opamps and dedicated comparator circuitry in there to actually detect that stuff.

and well, those leads are coming on. You know that's not like the process of turning those on or something like that. That's all analog stuff, so that's not good. And I'm getting nothing on the source output either.

I mean the lead's coming on for the source output I mean looks like we're getting something there, but trust me, whether or not I turn that Source off or on 1V uh Peak sine wave or different types of output W for not nothing. so Source ain't working. Oh well, what can I say I tried. Um, yeah, there's going to probably be some more videos run out of time yet again.

Um, this is all I'm going to do for today, but hey, we found a couple more negative. uh. voltage Regulators failed so clearly that power the original power supply. fire on that negative uh 18 volt rail has taken out.

um, at least three. uh, voltage? Regulators But all the other rails look fine. So we're now and we're getting in the exact same ADC Gat array era now. So I don't know now I'm getting.

You know a bad feeling about that. uh minus uh minus 15 volt raow which went -9 shouldn't be a huge deal, but uh, you know that Diode was shorted out so all that power was going through there into the analog rail. so hopefully it hasn't taken out. uh, too much.

But maybe we have to go back. Now to the troubleshooting guy cuz once we you check your power rails, then you'd go systematically back through to your troubleshooting guide and that's probably what we'll do next time and hopefully we'll find the sucker. But anyway, H I was really hoping that would fix it all was, you know, pretty confident. sort of.

You know, 80% sure that fixing those Regulators would would do the trick, but no, clearly not. I've tried to press that ADC AC back in the socket and and no, nothing. So oh well. the saga continues.

Catch you next time.