....Part 3 of the crusty
hp 3480B/3481A voltmeter.
And finally the 3814A buffer amplifier plug-in, this seems to be quite an uncommon choice with only one range (10 volts), if fact there seems to be bugger all on the web, well apart from the catalog entry and the Jan 1971 Journal article;
https://www.hpl.hp.com/hpjournal/pdfs/IssuePDFs/1971-01.pdf![](https://www.eevblog.com/forum/testgear/test-equipment-anonymous-(tea)-group-therapy-thread/?action=dlattach;attach=1292890)
![](https://www.eevblog.com/forum/testgear/test-equipment-anonymous-(tea)-group-therapy-thread/?action=dlattach;attach=1292896)
Unfortunately the plug-in didn't seem to want to come out, not sure why it's stuck and I don't want to break anything trying to force it out (the front & latching mechanism are plastic).
View from the top, with shield/cover removed, not much to see here.
![Blah :blah:](https://www.eevblog.com/forum/Smileys/default/blah.gif.pagespeed.ce.iJS9qlFEPg.gif)
![](https://www.eevblog.com/forum/testgear/test-equipment-anonymous-(tea)-group-therapy-thread/?action=dlattach;attach=1292926)
And the bottom cover removed, revealing quite a lot of transistors for a single range DVM plug-in, possibly making this set-up the largest digital panel voltmeter I've ever seen.
![Laughing :-DD](https://www.eevblog.com/forum/Smileys/default/smiley_laughing.gif.pagespeed.ce._hfWAz_QHO.gif)
![](https://www.eevblog.com/forum/testgear/test-equipment-anonymous-(tea)-group-therapy-thread/?action=dlattach;attach=1292902)
The low serial number makes me think I'll struggle to find a service manual for it, possibly the third to leave the Scottish
hp plant.
![](https://www.eevblog.com/forum/testgear/test-equipment-anonymous-(tea)-group-therapy-thread/?action=dlattach;attach=1292908)
And a bit of testing after reassembly, oh dear my 4½ digit voltmeter has taken a downgrade to a 3½ digit DVM.
![](https://www.eevblog.com/forum/testgear/test-equipment-anonymous-(tea)-group-therapy-thread/?action=dlattach;attach=1292914)
![](https://www.eevblog.com/forum/testgear/test-equipment-anonymous-(tea)-group-therapy-thread/?action=dlattach;attach=1292920)
It zeros OK but seems to need some repair, as the 3.7V cell is reading a bit on the high side.
First things to check would be the PSU & +10V ref, then move on to a test plug (details in the crappy service manual from Agilent) to eliminate the plug-in, hopefully the fault is not with the plug-in.
This will have to wait, as I'm currently working on the 207A sweep oscillator.
David