Hi welcome to Tear Down Tuesday You've seen me mention my HP 3478a 5 1 half digit classic bench multimedia before used it um in quite a few videos. well you may have noticed behind me I have upgraded Tada the HP 3457a 6 and2 digigit multimeter. Big score on eBay Got it for just over $ 150 Australian dollars. Fantastic and it's bang on beauty.

So I thought we'd crack it open see what makes it tick? Could be interesting? Let's go and here it is. Hooked up to my MV 106 transfer voltage standard you've seen in that previous videos. Yes, I did violate my uh don't turn it on take it apart rule here I just wanted to uh uh, tweet some photos and uh, check its performance before I go rip the thing apart today on Tear Down Tuesday and as I said, got on eBay for like 150 bucks and it really is a very nice meter. It comes with cow stickers.

It's a couple of years out of date, but still, that's not bad at all. We'll have a good, uh, close-up view of it, but um, here it is it. I've hooked it up to the MV 106 I've set it to 1.000000 volts. I've only got uh, five, uh, decimal places there.

This thing of course has six decimal places. It's a 6 and 1 half digit meter. In fact, technically, with some uh averaging in highres mode, it's capable of uh 7 and 1 12 uh digits. but you can't get that via the front panel.

Apparently you have to do that via the Uh Gpib remotely. So I do get fairly lucky with uh, these bits of gear on eBay Absolutely bang on. And of course, if I dial that up one digit there, you can see it basically changes by uh, 10 least significant digits. There's a bit of noise, there, a bit of fluctuation.

We can maybe change the Uh Power Line Cycles or something like that. So anyway, uh, if you want me to do a separate uh video on, uh, using this thing and having to play play around with it, uh, let me know. So that's actually not a bad upgrade to the uh, uh, classic HP 3478a This one's a 3457a and while it's not a Metrology uh grade multimeter like the Uh famous 3458a, this one's a 57a. Don't get uh confused between the two.

it is still a very impressive instrument. and really, it's um, hard to beat for any modern multimeter under 1,000 bucks for example. So you know to get this thing for 150 bucks. It's a bargain, so they're certainly worth uh, paying a couple hundred bucks for.

If you're in the market for a 6 and 1 half digit multimeter, its performance is still pretty impressive. It's a 1980s vintage, uh, mid to late 1980s I'm not sure when this one was actually uh designed. We'll find out manufactured. We'll find out when we crack it open by the Uh date codes on the chips and things like that.

But yeah, it's still a pretty darn good meter. And of course it. uh. One thing my 3478a doesn't have, it's actually got a uh micro amp uh range as opposed to milliamps.

So there it is. Bang! look at that so that's 100 Pico amps resolution. Very, very nice bit of Kit indeed. And uh, in terms of you know, uh, basic DC volts Accuracy on this thing, like the 24hour spec on this thing is pretty good.

It's down in the order of, you know, 18, PPM or uh, something like that. It's quite a nice bit of uh kit, so if you can pick one up for a decent price, highly recommend it. Now, while it may look like a big bit of Kit sitting on your bench with its big wide, uh front like that, you can see it here compared to the 3478a, which is actually quite, uh, deep and it's actually not that much physically bigger in terms of volume at all. And it's not that much heavier either.

which uh, means that you can get um, shipping usually for quite a reasonable price on these things even International But as always, some uh, equipment dealers like to uh, rip you off I Got this thing um delivered via DHL for like 70 bucks or something. So for me, it's a uh, worthwhile upgrade just for the uh DC current uh range. That microamp, uh, range capability. The accuracy of this thing uh I won't go into specs on this if you want me to do a review of it so you know, compared to it or something like that, let me know.

But um, yeah, the specs are a little bit better than 3478a but it has got some additional ranges and all the math uh, capability and stuff like that as well. so a better instrument all around basically. but it has that larger uh, wide, uh form factor whereas this one is, you know, half wit half rack, uh, width so that's probably its main disadvantage is that it can take up, um, some additional Uh space on your bench. In terms of Uh width, you know, instrument, uh, width on your um shelvin.

But apart from that lovely bit of Kit I Love it! And here's the front panel for those Uh playing along at home: DC volts, Ac volts, ohms, uh, 4, 2, and four wire DC Current AC current and uh frequency measurement as well. and it's got um Range you know Auto manual range selection, display digits and 6 and 1/2 digits. As I said, it is technically capable of Uh 7 half digits, but getting that to uh work on the front panel is uh, not possible I Believe you've got to do it via the Gpib as I said, and if we take a look over here at the configuration buttons, we've got number of Power Line Cycles So you change the Um integration time effectively, the Uh update time and that Uh averages things out for you. It's got Auto calibration Auto zero offset compensation Uh, it's got various Uh triggering capabilities and it's got an input Uh scanner, an optional input scanner as well.

but they're usually a very expensive Um option to uh, like. you can have multiple input channels as we'll see, there's um, a slot on the back to actually do that. This one's not configured with that and you can uh, uh, store and report and recall various Uh configuration settings. And then there's the Uh math capability.

Now, unfortunately, this thing doesn't have a huge memory uh on it. it's only I think it's only 1K or 1 and A2k or something like that and I'm not even sure if uh, that is the number of readings I think it's actually less uh than that number of readings depending on the resolution mode you've got this thing in. So you know you might only be able to store a couple hundred readings. but you can certainly do some usable math and get math and get standard deviations and stuff like that.

And of course, we've got proper binding post uh inputs here. It's got four wire input uh for ohms and separate current fused current. Uh, terminal down here. Now there's one minor disadvantage compared to the 3478a this one's replacing in my lab here.

Um, it's only got the front panel terminals. It doesn't have them duplicated on the back for my purposes. Doesn't matter a rat's ass, but if you've got you know, wiring these into a production, uh, test rack or something like that, that sort of thing could matter and check it out. It does have calibration stickers on it.

Uh, unfortunately, it didn't actually come with the calibration certificate of course. but uh, it's fairly recent. Uh, you know. April 2011 That's not bad at all.

I'm certainly not going to complain about that and that's a reason why it's bang on cuz these things you know They Don't Drift much folks. So really, once you've uh, you know if you got it calibrated a couple of years ago, I was pretty confident I saw this in the ad and I went well. you know that's good enough for me. I'm you know, taking a bit of a risk.

but I I thought this one would be bang on and it was now. Interestingly, it's got Analog Devices on here and it seems to have come from Um owned by Analog Devices themselves and they presumably have their own internal uh calibration Metrology Department which calibrated this thing and we've got another sticker here telling you what capabilities it's been calibrated over voltage, current, and resistance. Not a problem, by the way, it's it was calibrated in 2010 I Presume it wasn't calibrated again. Uh, after that, they probably just let the thing, uh, expire, but still, that's pretty recent.

It's got a sticker here that says Adpi I I'm going to guess that stands for Analog Devices of course. uh production instrument so I think this was used used um in their production environment for manufacturing The Analog Devices Chips One you know, those automated test racks and something like that, which is why it's in, you know, fairly good. uh Nick for its age really and uh, it's got a sticker from test Equipment Depot but I didn't actually H get it from them I bought it from another eBay dealer. so I don't know whether or not they got it from them or what the deal is there.

and it's made in the good old Us of a serial number 273a A stands for made in America and that's the actual serial number 11,838 no option 700, just the standard option. and there's the slot for the Uh scanner as you can. There's no Uh panel on that didn't come with it, but there's the internal connecting cable for that Uh scanner module. You can pay a couple of hundred bucks for those.

uh, low EMF uh Reay switching uh modules. so unless you're really need that capability, um, don't worry about it one bit and it's got Gpib of course. HP IB uh as they call it and it's got a Voltmeter complete output so a signal uh 5V TTL signal when the Uh when it's actually completed and an external Uh trigger input as well. Standard Ioc Mains and switchable from Um Uh 110 to 240.

so not a problem. Uh, doesn't matter where you buy this thing, it's going to be usable. and we've got ourselves a couple of: calibration void if, uh, seal broken stickers so we'll go right through those Lovely. The feeling uh you get when you crack open the warranty void is still sorry.

Calibration void if, uh, seal broken sticker Fantastic. There's no screws on the back of this thing. By the looks of it, it looks like it's all sort of done from the bottom here. So I don't know whether or not these screws go all the way through or not.

I'm not sure what the deal is there. Yeah. I think they do. the I presume that the top.

Those things don't fall out. Lovely design there. captive screws, so this should. Yep, Tada just lift straight off.

beautiful, all shielded. That's what you'd expect in a 6 and 1/2 digigit multimeter. Warning: this panel connected to terminal low and that's not surprising at all. that internal Shield there is connected to your ground.

It's it's not connected to uh Main's Earth It's just connected to the ground on the front panel and we can verify that by Main's Earth There and there we go, There's no connection whatsoever through to the Ground Terminal because of course it's uh, floating. That's what you'd expect in a multimeter, a bench multimeter like this. But you'll probably find that this power supply Shield over here is connected. Yeah, there we go.

That one is connected right through, but this one is just internal. uh, ground connected For you know, it's all part of the system ground design to uh Shield all the electronics and uh, in short, there'd be lots of low EMF uh design in this, lots of staro grounding and stuff like that. and they've deliberately kept it from Main's Earth as or part of the system ground in functionality to ensure that they get the 6 and 1 half digigit performance in this thing. So this grounded top cover here and when I say grounded I actually mean ground and not Main Earth as we just saw, there actually is connected through to the bottom cover down here which is also uh, separated from Main's Earth over here.

So that one is just the Uh shielding cover for the Uh relay input switching Matrix board which then slots in underneath here so we should be able to lift that out and somehow it's got instructions there should read it, and if we just flip that uh cover open, it's uh, held on there via this ribbon cable. it's a attached on and won't disconnect that unless I absolutely have to. but uh, you know. Warning caution Caution: We've got some uh, we've got a gain and flatness control here that warns you that it's input High uh, that's connected to the input high potential and there's a V offset adjustment as well.

So, but they're the only two adjustments that you can uh get through this thing. So we should be able to lift this plate off and see the Uh measurement and Uh acquisition board on the bottom here separate from the power supply and digital Uh display board. Over in this part, you can see the ribbon cables go into the Uh keypad and the LCD and stuff that all digital control. There'll be some RS under there microprocessor, but this is all your interesting measurement stuff under here.

So it looks like this thing just unlatches y there some sort. There we go. You just push these latches back like that they're not easy, but unlatch this side first and then you probably got to unlatch this side over here. Yep, there we go and that's a nice design I Like that t look at that oh can see the voltage reference board straight off the bat and uh oh, lots of Reay switching.

Oh good stuff and one of the first things I Noticed of course as part of the Uh system design keeping these grounds separate, you'll notice that there's only two connecting cables on this thing. One is coming from the Transformer over here. so it's got its own transformer tap going over there that's of course isolated due to the Uh Transformer. Then it's got its own uh, just linear rectifier and linear regulator over here.

And then down in the bottom is the only other connection between the digital board down here and the Uh and the main signal. uh, processing board and ADC board over here and you'll notice that it looks like there there it is Opto isolated and you can see that Opto isolator down in there with the big slot going right through the board. They've even cut this uh, ground, uh, earthing Trace over here cuz this would be connected. You'd just ruin your Uh system ground if you connected that straight across.

So they've actually cut that straight through with the slot. and they've used these Opto couplers here. but they're They're like one of those uh, opto couplers you'd see. you know, um, uh, like in a photocopy or something like that where you can actually put uh something in between like that and it just cuts off the signal between the two.

So that's rather interesting. I Would have expected to see a you know, a basic uh dip package, opto couple or something like that, but they've gone with that type so they're doing that to keep the entire ground system separate. This is the grounding point. so if we measured say this, uh, screw over here.

it' be on the metal shield that would be going through to the ground connector on the front panel. And of course this one over here is uh, connected through to Main's Earth as we saw in the measurements. For now, my idea for why they've chosen that type is it's probably just uh, basic built-in braces engineering. These type of, you know, going to have a larger Um withstanding uh, voltage, larger isolation voltage just purely because of the huge physical Gap and isolation between the Uh phototransistor and the diode on this thing.

So yeah, my guess is it's uh, they were much better than the Dip package, So maybe they just had a higher withstanding volum Then say a standard 4 N25 Opto coupler or something like that. But yeah, I don't know. you'd have to actually get the data on that one. but even your standard opto couplers are pretty darn good.

So I don't know. maybe there's some serious belt and braces happening there. And there you have it. It's not a 1980s vintage folks.

sorry to disappoint you. It's uh, 42nd week 90. That's probably around about the earliest date code I can find on this thing. The chips seem to be around the 40 or 50th week 19 90 so I'm not sure when they actually stopped manufacture on this thing.

If you actually, uh, know the uh, start and end manufacture dates on the 3457a, do let us know in the comments or on the Forum. I've popped the top cover off the processor board here and you can see the uh, lovely power switch extension bar there going all the way back. I Love those extension bars. Great engineering and uh, there's the backup battery in this thing.

Lithium battery. Check it out, folks! Made in Britain Hi to all my British viewers. Uh, it's an Eternos cell 3vt battery and uh, it doesn't look like it's leaked at all. You have to be very careful.

By the way, when you're opening these things, servicing them, pting, and poking around in these things, don't short out that battery at all and don't replace it with the power off because you will lose all your calibration data in this thing. So I'm going to check the voltage on this. make sure it's still good. Now make sure I don't have my meter set to amps because that would be really embarrassing I'd short out my battery and I'd lose all the Fantastic calibration and the bang oness if that's a term I'm going to invent it.

um of this thing. so let's have a look. Tada There we go. 3.06 volts.

Beautiful! I'm not going to touch that sucker now. This is interesting. This processor board seems to have been manufactured at a different time. Uh, 4 years prior to when the ADC board.

Most of the 74hc chips on here all seem to be dated 86. Look at that. 40th week, 1986, 44th week 86. All within the same.

Uh, you know, all within the same order. 23rd week, 86 up here. So almost every one of them. So that is weird why that processor board was clearly manufactured.

Um, you know, around 80. Well, I'm presuming around 86. Otherwise, they bought an absolute buttload of these chips back in ' 86 and they were still using them 4 years later. Uh, I don't know.

Um, it doesn't. You know it, it doesn't wash. I mean all of them. The Intel processors all these chips all around 86.

Whereas all this board over here is all 1990 vintage Me: Check it out. Even the system ROM has a date code of fifth Week 1987. My guess is well, this is a 1987 vintage instrument, but it's had a complete upgrade of this board in 1990 or so. That's the only conclusion I can come to.

Now this is really interesting. Check out all of these uh dip parts around here, including this, um part here on the voltage reference board here. They're all got 1826 Das something four, five linear Tech Parts there plus National NTI Yet they've all got that same 1826 Dash and then a number like 1382 and uh, you know, 0521 and uh, 1265 and all sorts of stuff. So it looks like HP have had these sort of like, uh, custom branded.

They're of course, are off the-shelf Parts They aren't like custom chips, they're just regular off the-shelf Parts But they've had them rebranded, possibly with the HP part number. now. One thing you won't find in a Precision instrument like this is a cooling fan. Why? well a it, it doesn't generate a huge amount of heat.

I Think this thing's rated for like a 30 WS maximum consumption or something. It could be uh, a lot less than that in actual Uh Power drawer. But because when you have a cooling fan in there and it's sucking air through the side vents for example in a typical product and then going out well, you're creating thermal gradients within the product and over the parts in particular the voltage reference down here, which we'll take a look at and other parts of the board. And you don't want thermal gradients because if you've seen my thermocouple video, you'll know that basically any dissimilar metal Junction within this unit any Junction at all solder and copper, uh clad board and everything else creates dissimilar metal Junctions acting as a thermocouple.

So you're going to get EMF voltages generated in the unit so you don't the last thing you want in something like this. you would rather have it heat up to a warm temperature and stay nice and even than try and cool it down with the air flow through the thing and we can demonstrate this all right. What I've got here is my resistance standard. Uh, hooked up to this thing.

It's close enough to 10K here, so this least significant digit here represents one PPM of that 10K So one parts per million and you know this thing, it's Tempco is incredibly low in the order of like, you know, parts per million. So any uh, you know, change in temperature in here can actually generate um, uh, EMF small EMF effects which can affect or thermocouple effects in the joints. uh, or a temperature gradient across components that can actually affect the reading when you're talking down in this region now I can wave my hand around in here so it's not noise, pickup, or anything like that. Okay, so what I'm going to do is actually breathe on the circuit in here and you should see this sign signicantly change.

Let's give it a go. Look at that. There you go that's changing by like hundreds of PPM Look at that hundreds of PPM just by breathing over that circuit there. So that is a really big deal for a 6 and 1/2 digigit Precision meter like this.

So that's precisely why you won't find a fan in a Precision bit of Kit like this. You do not want all that air blowing over and creating those uh, temperature differentials across your component. It's a big no no. and if you take a look at the processor board down here, somebody's actually texted on the serial number for this unit 273a 11838 and then a date code in 93.

So something and some other numbers there. So something was done to this thing in 1993 I Have no idea what that is a couple of years after the or 3 years after the Uh 90 dated chips 1990 data chips on the analog board. As for the main board here, we have more HP custom part number branded chips. Here's the main processor u601 here and it's some sort of Motorola part, but it's got this 1820 2624 part number and that looks like a HP part number like here the these resistant Networks look these are these are all 1810 and 1820.

You'll also find down here. Check this out here we go. here's a national part 1820 as well. Here's another Harris I think that's a Harris part down here 1820.

There it is again. um that I believe is the Uh keyboard. uh, front panel keyboard controller cuz it uh goes down to the ribbon cables to the front panel or the Um LCD um sorry the Lcd's got its own controller, but yeah, they got these freaking custom part numbers on them. Real pain in the ass.

And here's the Uh schematic which I'll actually uh Link in in the notes below so you can load up the PDF of the service manual. It's got the full schematics in here. They're a little bit hard to read, but there's the main processor U uh 601 there that we looked at and then of course it's got uh, you know, the RAM and ROM. It's all very, uh, traditional stuff down in here.

all miscellaneous control stuff. We got the speaker down there. nothing really, uh, majorly important there. and then, yeah, here's an extension of it.

It's one of these big long schematics, so it's got to be broken up. We've got our Hpib SL Gpib, uh, controller stuff around here. We've got, um, the nonvolatile ram control. There's our internal battery there, so you can see how that just, uh, continually powers that.

It's just diode or there. and there's the right calibration lock circuit as well. Watch doog, timer, It's all there. All pretty.

uh, basic digital stuff. But what that actual Motorola processor is? I don't know one of the Motorola 8bit processors most likely. And then we have our opto coupler link between boards. and that's what we looked at.

Um, down below. That's that. uh, there you go. It's just serial uh in and serial out data connecting the two boards together.

And of course. uh, this analog board over here actually has its own control processor. and there it is. that's an Intel 8051 microcontroller.

And look at this National device here. that's actually don't know if you can hear that, but that's actually not plastic anything that feels like and sounds like, uh, Ferite. So they've surrounded all of the leads on this chip here. Kind of like, maybe is an afterthought.

Um, that they've put like, a little effectively, a little Ferite bead through each one of the leads on that National semiconductor device. I Wonder why? And of course, we don't know what the bloody chip is cuz there's one another. one of the stupid part numbers 1820-30 4. Oh, and here's another device down near the Um.

input down here. What the hell is this doing? This is an 1820 D38, 61. Oh man, but thankfully, of course you can uh, pretty much tell what that's going to do based on the proximity of these relays. I don't see any discrete Uh transistor drivers for all these Uh relays down here.

so that's probably a relay driver chip. and if you have a look at the schematic TDA there it is. Relay control you 121 and you can see a whole bunch of Uh catch diodes there which are the uh, get the back EMF of all the switching coils, but uh, basically all of these relays. Um, they're going to be used for, um, not only switching the inputs, but uh, used for the Uh test modes as well.

They can short the inputs, they can disable them, and uh, route them through to other test signals cuz this meter has a fairly uh, comprehensive built-in self test. So this 8051 microcontroller it, uh, basically You Know It uh does the reays. It handles the Uh optional input switching card which sits on the top, and basically Uh handles the ADC as well. And there is the custom hybrid ADC in this thing.

This one ain't off the shelf by the looks of it. So there you go: I have no idea what that ADC is. Um, it's a, you know, some sort of maybe HP Uh custom hybrid ASC ADC or something like that to get the performance I don't know. and here it is u51 That's the hybrid looking custom ADC thing there or with it.

you know that's the entire ad uh converter circuitry around here and you can tell you know we really start getting into our Precision measurements here. We've got guard nodes marked around here matched transistor, matched Jfet transistor Pairs and uh, stuff like that. And here's our reference board over here that's got our reference Zena on it and we'll take a look at that. but uh, yeah, that um ADC is of course, clocked and controlled via the 8051 processor.

And here's what a lot of people want to see: what is the ref: the voltage reference used in this thing. Well, this is the Uh PCB assembly here. This one is obviously the Uh reference um Zena Diode with a building heater too, of course, but it's a linear technology part. but once again, that custom HP Part number 1826 d249 D5 with a date code of the 36 week 1990s.

And once again, we've got another linear Uh technology part over here. but once again, HP part number branded. but that's just a Precision opamp. uh, clearly.

so there's you know, there's nothing else going on there and it uh, generates the Uh PL I believe plusus 10 volt reference voltages, which we should be able to measure on those two test points I'm assuming and I'll just verify that I'll just probe I assume that that uh nut, there is ground. so I'll just probe that. Yeah, Minus 10175. Of course it doesn't have to be precise because the uh, um, and of course it's exactly there you go.

The positive is the exact opposite of that. so it generates Plusus 10vt supplies and they don't of course have to be spot on because this thing uh, compensates for that with the calibration values in the software. And of course, the key to an instrument like this is not its absolute accuracy. As I've said before, that voltage reference down in there it can be plus - 5% absolute accuracy.

You don't care what you care about is the temperature coefficient I.E the Uh drift per degree celsius. How many PPM per degree celsius drift? Is it 100? PPM Is it 10? PPM Is it one? PPM You know, really. Precision Stuff like used in say the 34 Uh 58 a for example, one of the world's best multimeters in the big brother to this one. Well, it's not about its absolute accuracy.

You can just trim it to anything you want. It's all about the drift. Now this reference board here as I mentioned. uh, the designator is A25 and it it's exactly the same HP part number as the one used in an earlier model 3456a, which we do actually have the schematic for.

And here it is the A25 reference board O3 456 6525 And that's exactly the same part number as what's used in this Uh 3457a And as you can see the same Uh four pin device here with the internal heater like that and there's the internal Xena Diode. and of course, it amplifies that. And of course, there's not much to it. It's all about the stability of the Xena diode itself.

You know, very carefully selected, very carefully. Uh, tested and characterized for the performance in this thing. And you know there's nothing else on this board. There's one 2, three resistors and a cap and that's exactly what I see on this board.

three resistors and a cap. So it's an identical board. and the service manual for this instrument gives u500 listed as an LM uh 299h and that's the classic um National semiconductor reference, but the one we've got here is a linear Tech technology so and what, but it's still four pins. and in case you're wondering, it also lists U501 here, which is just an Lm1.

Now, it's hard to actually get in and see under there, but I can actually see it. and this is actually a four pin device. So clearly, uh, two of the pins are for the Zena Diode and the other two are for the heater. and you can see there that we're measuring.

you know, roughly like 42 43 or something on that um on that chip I The laser is not directly on it cuz there's an offset there when it's up close, folks. So I haven't let this thing warm up to uh temperature, but you know if you move it to the side you can see that that is obviously got a heater in it to heat up the Zena and that would be uh temperature uh, controlled as well to keep that at a constant temperature. And if you have a look at the Uh input terminals down in here, yes, they are just wired uh, directly across like that. but they do go through a too filter.

they're wrapped around in there quite nicely heat shrunk down in there and then they go directly into the reays bit because this uh thing is all metal, uh, grounded shielded stuff like that. You can uh, get away with uh those effectively quite long leads going from the input Terminals and there's a 1.1 ohm high value resistor that's uh, most likely our input Uh current shut resistor and you'll notice all the star grounding branching off from from that point really is quite nice. and this board mounted on top. here.

this is the AC converter boards doing all the true RMS uh stuff and AC conversion. couple of switchin relays and those adjustments which we saw in the Uh top uh through the top metal uh can and yes we've got more HP part numbers look at that 1826 there 1826 up there for that, an log devices part and more of them all the way up the top. HP Part numbers is far as the I can see and if we pop that AC converter board out, there's only two wires. uh Levering that thing on nice uh silk screen designators all on the bottom there component designators.

It's also got its own metal shielding can so we should be able to remove that and woo hello and looku what we have here folks. We have a whole bunch of uh, well, they. at first glance you go well, what are they? They don't look like the other reays, but of course Kotto is a dead giveaway. Cotto is a very uh, high quality manufacturer of Um Precision uh low EMF re read relays and stuff like that.

so these are 04 90-15 Haven't been able to find the exact data sheet for that one on a quick glance, but they would, yeah, be some sort of maybe shielded or uh, low noise low EMF uh, relay or something like that. but we've got ourselves a hybrid and we also have ourselves a genuine Bodge. Check that out, they've even heat Shrunk The leads look at that. Beautiful and a look at our schematic folks.

Reveals All u101 is the input hybrid board there and it's got all the Uh switch in. Look at that. all the Uh Fet switch in required for all of the input circuitry cuz here's our input circuitry over here. and here's the input circuitry here.

There's some Ohms over voltage protection there. Here's all our input put uh, relay switching stuff. There's our input fuse by the looks of it, and various switch rain switching stuff. So like, you can sort of equate that to say, similar to, uh, like a fluke Uh custom input switching hybrid that they use in their multimeters for example.

So that's all on that one board and that would be very well matched. And then of course the output of that goes into these matched Uh transistor pairs here. Precision Op amps and various other stuff. So you can, you know, take a look at this uh schematic until the cows come home.

But there's the Ohms current source for example. Great stuff. There's the input amplifier which I said, and there's the match transistor Pairs And then we've got a pre-charge offset circuit and an offset Dack as well. Now that certainly is a very interesting hybrid board indeed.

obviously. uh, all the circuitries on the bottom. they've just got got this big uh ground plane on the top here. There's only one extra trace on there apart from the ground, and it's actually held in by these two screws.

and it looks like they just, uh, press into those pins those gold plat pins sticking up from the board. so I should be able to undo those and uh, lift that board off without any damage. Well, sorry folks, that's not the least bit exciting. It's all, uh, encapsulated.

It looks like it's got epoxied in you could. probably, you know, if you wanted to ruin this thing, you could, uh, un, you know, take off the epoxy or break through the epoxy on the outside of that and then uh, have a look at the Hybrid under there. But of course I want my unit to work? so I'm not going to do that I'm just going to put it back and we've got ourselves a little uh, metal can B BR package down in there and the obligatory trim pot. Now there's one thing I don't particularly care for on this AC converter board is that it's only held down by that one screw there I Mean, the board does go through over here, but it's not like it's really held in place with that at all.

So there's only you know I wouldn't like to, uh, know about the uh vibrational mode set up during transporting that thing I not impressed by one Mount like that at all. So there you have it. That's about all she wrote for the HP 3457a Um, sorry I just can't go into more detail on some of the chips. I could try and reverse engineer some of them.

uh, figure out what they are, but really, um, it's it's tough when they brand the things with just generic HP part numbers. Real pain in the ass. Anyway, if you want to take a look at this thing, the Uh service manual for this which has the full schematics and everything else in it will be linked in down below. and uh, if you know what that voltage reference is in there from linear technology, please let us know I'm sure there's a lot of people um, into, you know Precision references on the Forum and uh, stuff like that and they would love to know that sort of thing.

Maybe it's obvious I don't know I just haven't looked hard enough. But anyway, if you want to discuss it, jump on over to the Eev blog Forum that's the best place to do it. and if you like tear down Tuesday Please give it a big thumbs up. Catch you next time.