EEVblog

Inside the HP 3478A Multimeter
A quick follow-up to the previous 3457A teardown video.
Forum Topic: www.eevblog.com...
Photos: www.flickr.com/...
EEVblog Main Web Site:
www.eevblog.com
EEVblog Amazon Store:
astore.amazon.c...
Donations:
www.eevblog.com...
Projects:
www.eevblog.com...
Electronics Info Wiki:
www.eevblog.com...

[@richaw42]

I was one of the engineers that designed the HP3478A. Battery: The battery in my 30-year-old prototype measures 3.011V. The design life minimum was 10 years, probably at maximum storage temperature. Shield: At least in the prototype, a small shield was needed to calm down the AC RMS converter. In initial production, it was just a large disc capacitor. Inside the micro, there is another digit which was pretty good and could have been displayed. I wish I'd left that test code in my prototype...

[@RiyadhElalami]

That must have been amazing to work on such devices back then. Any interesting stories?

[@madkins0128]

Wouldn't there be a way to examine and record the calibration information and reload the ram with the calibration information after a battery change out?

[@lohikarhu734]

Hi Rich; if you are still lurking here... I have a 3478A, with an Asset tag "0001 Salo" :-) Maybe you know about Salo FInland in the 1990's ;-)

[@JosipMiller]

I am proud user of this beauty. I inherited this instrument from my retired and then departed colleague who sadly passed away in 2014. There were quite a few beautiful instruments and tools all maintained and calibrated nicely to this day. There was also 3465A 4 and 1/2 digits which required massive cleanup of switches and works perfectly now. 3478A we calibrated in local calibration facility and looking this calibration report was really impressive. There was almost nothing to calibrate in 2018. on instrument from 1990. Only correction was made somewhere in current measurement. Original battery is still inside. What I forgot is to replace filter capacitors which I intend to do before next calibration as well as replacing the battery using isolated soldering iron and backup battery. It has 4-wire resistance measurement which was extremely useful during development of sensitive temperature measurement equipment. Very often I make my own check-ups with voltage reference but proper calibration is needed anyway.

[@bitrexgm]

I have a unit I got surplus for $50 from around the same period,, no calibration sticker on it so I don't know if it was ever calibrated since new. Out of about a 60 point calibration test suite I had done by Essco only one measurement was out of spec, the 1.899841 MOhm test resistor read 1.89942 on the 3 MOhm range.That's it!

[@seamonkeys12y]

I got a HP3478A, the battery of mine still appears to work fine but I made an arduino GPIB adapter to grab the calibration data just in case. Maybe the previous owner of it replaced the battery though

[@N1CH0LAS12]

I really enjoy watching your videos. I love the fact you're very smart and will admit you don't know something and ask people to tell you the things you don't know.

[@ChipGuy]

Thanks for the video, it make me realize that i need to use one of these 2Ah Lithium primary batteries instead of these 290mAh CR2032 cells :) Love them teardown vids :)

[@MrFreeElectron]

slope error means the rundown failed to close. check the integrator and comparator. most likely the comparator is shot.

[@stevenspmd]

@EEVblog just picked one up for $110 usd but shipping by UPS was a kick in the nuts

[@CassegrainSweden]

Regarding exchanging the battery, I would use an isolation transformer feeding the unit on which to exchange the battery. Gives no galvanic connection to the soldering iron.

[@davadoff]

Why not just unplug the HP multimeter? Why isn’t that sufficient?

[@PaulTurner_Haizo]

Yes, they certainly could be toroids, the service manual that shows how simple to do that is. but the board layout doesn't match. Maybe it is indeed a later opto-isolated model?

[@BryceSchroeder]

For me the critical difference between the 3478A and the 3457A was that the latter was specified to measure AC current at 100 kHz and the former wasn't. It's so hard to find any instrument at a reasonable price that is specified for current beyond 10 kHz... the 3458A is another that is, and Fluke has one that _might_ be, but the spec sheet was ambiguous. I wonder if it's just a specification / testing issue or if that current measuring shunt really is a huge bandwidth hit? (All of them advertise 100 kHz or so AC volts bandwidth.)

[@lynxgroupblog]

Dave : remeber those gas powered soldering irons ,they do wonders in this bettery replacement ?

[@GabrielRotar]

Learn something new every day I guess, Cheers mate.

[@yoramstein]

hi does anybody hasthe link to the cross refferance guide to HP's parts?

[@gglovato]

interesting note, it accepts from 38 TO 440Hz! (aircraft power bus), whilst the other biggie one had a very limited input freq range....

[@frankbuss]

The forum link doesn't work. Looks like it expects a trailing slash. Might be worth to fix the forum software, so that you don't have to fix all links in all your videos.

[@StuartTaylorEsquire]

Ahh fer cryin out loud Dave. I've been watching a few of these metres on eBay, go for less than £50, then you start posting blogs about it, and guess what, £170 overnight ffs.

[@debug_duck]

try to ask on the forum there are probably more people reading your problem who can help you

[@Razor2048]

Couldn't you use a butane soldering iron to desolder the battery while the unit is powered on?

[@RandyLott]

Is it typical for one person to design the PCB, or is it divided between a few people? Thanks Dave!

[@playstation2bigs]

first time to see HP multimeter

[@rameshmano7401]

how to convert from 110V to 240V input

[@GabrielRotar]

is that voltage reference a bit loose on the board or just it's casing ?

[@michaelnobibux2886]

there could be tiny toroidal transformers embedded in the 8 pin dil packages,i ‘ve seen this on old pcb‘s!!!

[@adkharu]

hey Dave. i purchased one of these units from a US seller and it appears to be an identical model. i would set the dip switches the same because i live in Australia. did you need to replace the fuse? also, the service manual says to internally change the Line Select Jumper. is this necessary? thanks for your time. -ak

[@vink6163]

This might be a silly question, but what is the benefit of having that extension bar from the front panel to the power switch, as opposed to having the power switch sitting just behind the front panel? Is it to do with keeping wiring emitting a 50/60Hz signal to a minimum?

[@davadoff]

Attention to detail. If the switch is at the front then you’ll have to run mains power to the front then back to the rear again. It might also use up space at the front needed for low voltage stuff.

[@123456789robbie]

i don't understand, what do you mean by a half digit?

[@ScramblerUSA]

These 2 DIPs could be transformers, actually. Like TDM-250NE from Halo Electronics.

[@AeonFlexMusic]

good review

[@blizniak28]

Dave, tell us something about Swerleins algorithm !

[@ekkrir]

factory power settings for 120V AC?

[@Quark.Lepton]

You'd have to have x-ray vision to see the damn display.

[@keriksen2749]

I just got one of these meters worked for two days reads accurate, but I now have this on display. C: Anybody knows what that means? Thanks.

[@rainbowsalads]

that shield at the end is weird. : /

[@juanolmosmendoza5361]

Hello, how are you? I bought a multimeter HP-3468A for a bargain of 25 dlls because apparently the previous owner tried to change the battery that enables the calibration function and the information in the ram memory was lost nec UPD5101L_NECElectronics and I realized that in one of your videos you made a repair of a multimeter of this model so I am interested to know if you could clone the finware of this memory and sell it to me to recover the functions of this multimeter

[@juanolmosmendoza5361]

Hello how are you doing? I bought a HP-3468A multimeter for a bargain of 25 dlls because apparently the previous owner tried to change the battery that enables the calibration function and the information in the ram memory was lost nec UPD5101L_NECElectronics and me I realized in one of your videos that you did a repair of a multimeter of this model, so I am interested to know if you could clone the finware of this memory and sell it to me to recover the functions of this multimeter I already made this comment in another of your videos I repeat it in this video to see if you could answer it I would really appreciate it

[@whatsmyusername1231]

What is this "Diode or'ed" you speak off?

[@MrMac5150]

Hey

[@99959bill]

Hey Dude how about selling me that 3478A!! Eh Eh?? I sure could use it! Pay Pal Payment!!!! Bill

[@aerofart]

Fourth

[@aerofart]

Really? Who gives a rats'-ass?