# HG changeset patch # User David Douard # Date 1479851431 -3600 # Node ID b027bc447b572dc7dd03f268da9fc3cd167fba75 # Parent 56bcb94f6ff5c10e8b13a375cd1ec439a6196353 [hp3456a] new blog post diff -r 56bcb94f6ff5 -r b027bc447b57 content/hp3456a.rst --- /dev/null Thu Jan 01 00:00:00 1970 +0000 +++ b/content/hp3456a.rst Tue Nov 22 22:50:31 2016 +0100 @@ -0,0 +1,93 @@ +============================ + HP 3456A Digital Voltmeter +============================ + +:Author: David Douard +:Category: Electronics +:Tags: HP, 3456A, DVM, repair, test equipment +:series: HP 3454A +:series_index: 1 + + +A very long time ago, I bought a venerable HP 3456A Digital +Voltmeter. Back then, I had no clear idea what kind of device it is; +but it was cheap. It worked quite fine (it is indeed not calibrated), +but I noticed for a while that it was quite unstable: the last 2 or +even 3 digits (in 6 1/2 digits mode) were jumping a bit too much. + +Back then, I did not took the time to investigate the reasons of this +behavior. + +However, a few days ago I plugged it to roughly test the stability of +an old Time Electronic Limitd D.C. Voltage Calibrator I bought for +almost nothing. After a few hours, the display showed an overload +condition (display OL). + +So I started to read the service manual and to follow the +troubleshooting guide. At some point I reached the step where the +procedure requires a Signature Anayzer (which I obviously don't have). +I briefly tried to dig the signals with my cheap USB logic analyzer, +but the readings were quite disappointing. I was considering +implementing a signature analyzer using a Nucleo STM32 board, since I +have several of them for my `HP 34970A display replacement project +<{filename}/hp34970a.rst>`_. + +Suddenly, I realized I did not even check the power rails! And +bingo, the +33V was dead (something like 5V). + +Ok, much better, a power supply failure is a way better +news. Especially since this kind of device uses a linear power supply: + +.. image:: {filename}/images/hp3456a/psu.jpg + :alt: HP 3456A's power supply board + +Yes, it is very dusty. +The culprit appeared in plain sight as soon as I removed the power +supply board (A10) from the unit: + +.. image:: {filename}/images/hp3456a/psu_C7.jpg + :alt: failing caps on HP 3456A's power supply + +The schematic is very straighforward; few bridge rectifiers, some +capatcitors, some regultators, nothing fancy: + +.. image:: {filename}/images/hp3456a/psu_schematic.svg + :alt: schematic of the power supply board + +The dead capacitor is C7 (47µF, 50V, Sprague). I also checked the +other capacitors on the board, and noticed some of them were not very +tight. A quick inspection of the solder layer showed a few "cold" +solderings on C16 and C19. That would for sure not help the DVM to +keep it's accuracy and stability! + +So I replaced these caps (and cleaned the dust everywhere I +could). Unfortunately I did not have caps with the correct spacing, so +the caps I soldered on are not plated on the PCB, and the only +replacement cap I could find for C19 is a (probably) poor quality +noname brand... I'll have to order some better replacement caps next +time I have to purchase on DigiKey or Mouser. + +Whatever, after this quick recap, the 3456A is back alive: + +.. image:: {filename}/images/hp3456a/1.0011v.jpg + :alt: 1.0011V + +And even better, it look much more stable than it used to be! + +For example, here a plot of my Geller Voltage Reference a few month ago: + +.. image:: {filename}/images/hp3456a/geller_2016_02.svg + :alt: 10V + +and now: + +.. image:: {filename}/images/hp3456a/geller_2016_11.svg + :alt: 10V + + +It's time for a nice enclosure for my Geller Labs reference now. I +also still have in my todo list a DC reference built around a AD5791 +and a LT1100 I have. + + + diff -r 56bcb94f6ff5 -r b027bc447b57 content/images/hp3456a/1.0011v.jpg Binary file content/images/hp3456a/1.0011v.jpg has changed diff -r 56bcb94f6ff5 -r b027bc447b57 content/images/hp3456a/geller_2016_02.svg --- /dev/null Thu Jan 01 00:00:00 1970 +0000 +++ b/content/images/hp3456a/geller_2016_02.svg Tue Nov 22 22:50:31 2016 +0100 @@ -0,0 +1,24003 @@ + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + diff -r 56bcb94f6ff5 -r b027bc447b57 content/images/hp3456a/geller_2016_11.svg --- /dev/null Thu Jan 01 00:00:00 1970 +0000 +++ b/content/images/hp3456a/geller_2016_11.svg Tue Nov 22 22:50:31 2016 +0100 @@ -0,0 +1,5357 @@ + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + diff -r 56bcb94f6ff5 -r b027bc447b57 content/images/hp3456a/psu.jpg Binary file content/images/hp3456a/psu.jpg has changed diff -r 56bcb94f6ff5 -r b027bc447b57 content/images/hp3456a/psu_C7.jpg Binary file content/images/hp3456a/psu_C7.jpg has changed diff -r 56bcb94f6ff5 -r b027bc447b57 content/images/hp3456a/psu_schematic.svg --- /dev/null Thu Jan 01 00:00:00 1970 +0000 +++ b/content/images/hp3456a/psu_schematic.svg Tue Nov 22 22:50:31 2016 +0100 @@ -0,0 +1,284 @@ + + + +image/svg+xml \ No newline at end of file diff -r 56bcb94f6ff5 -r b027bc447b57 theme/templates/base.html --- a/theme/templates/base.html Mon Sep 19 00:25:06 2016 +0200 +++ b/theme/templates/base.html Tue Nov 22 22:50:31 2016 +0100 @@ -50,7 +50,7 @@ {% endfor %} {% endif %} {% endif %} - + {% endblock head %}