--- /dev/null Thu Jan 01 00:00:00 1970 +0000
+++ b/content/hp3562a_4.rst Tue Jan 03 18:21:20 2017 +0100
@@ -0,0 +1,126 @@
+==========================================
+ HP3562A Dynamic Signal Analyzer - Part 4
+==========================================
+
+:Author: David Douard
+:Category: Electronics
+:Tags: HP3562A, HP1345A, repair, test equipment, DSA
+:series: HP 3562A
+:series_index: 4
+
+This is the part 4 of the series about my
+`HP 3562A Digital Signal Analyzer <{filename}hp3562a.rst>`_,
+quickly describing the HP 1345A Digital Display unit as well as
+the repair I had to do on it.
+
+
+Display
+=======
+
+The display unit is a HP1345A Digital Display without the option 714
+(wich adds a 4K x 16 bits Vector Memory), so it must driven by a
+dedicated display controller (which is on the A38 memory board):
+
+.. image:: {filename}images/hp3562a/a8_a17_display.png
+
+The unit is a 6 inch monochrome display producing true vector graphics
+with a resolution of 2048x2018 points. It can display up to 3226
+inches of vectors at 60Hz. It also embeds a character generator.
+
+It's a true vector display; vectors are drawn by moving the CRT beam
+on the screen (it's not a pixel based display).
+
+.. image:: {filename}images/hp3562a/hp1345a_raster_vector.png
+
+It can diplay:
+
+- solid lines
+- solid lines with intensified end points
+- short dashed lines
+- long dashed lines
+- dots at end points
+
+with 3 differents visible brightness levels. It also allows to specify
+4 beam velocities:
+
+- 0.13cm/µs
+- 0.25cm/µs
+- 0.38cm/µs
+- 0.51cm/µs
+
+Allowing more brightness control of the vectors.
+
+.. image:: {filename}images/hp3562a/hp1345a.jpg
+
+
+If not connected with a controller, it shows a test pattern for
+adjustments.
+
+.. image:: {filename}images/hp3562a/hp1345a_test_pattern.png
+
+The unit looks like:
+
+.. image:: {filename}images/hp3562a/hp1345a_side.jpg
+
+.. image:: {filename}images/hp3562a/hp1345a_side2.jpg
+
+.. image:: {filename}images/hp3562a/hp1345a_top.jpg
+
+
+Adjustment and repair
+---------------------
+
+While the instrument was apart, I wanted to see if I can recalibrate
+the display, especially try to adjust the overall brightness of the
+CRT since mine is a bit dimm (I have to set the intensity knob FCW to
+see the whole picture). I also wanted to improve a bit the focus and
+precision of the lines.
+
+So I took the display unit off the instrument, which is
+straighforward, powered it using my benchpower supplies, and began to
+read the adjustment procedure and turn the pots, when suddenly the
+display shut off.
+
+Using an ohmmeter, the diagnostic was easy: the +15v and -15v rails on
+the A1 board were short. Fortunately, the schematic is available, so I
+started to look for all decoupling capacitors (directly connected
+between a power rail and the ground). It took me a little while before
+identifing the real culprits, since the only solution to check them is
+to desolder (at least one end): A1C45 and A1C48.
+
+.. image:: {filename}images/hp3562a/hp1345a_dead_caps.jpg
+
+
+These 2 small (tantalum) caps near U3 were short. Not sure why they
+died when I powered the display unit with my power supplies, maybe I
+set them to a bit higher voltage then what the HP3562A generates.
+
+I replaced them with the closer spare I found (4.7µF tantalum caps),
+and the Display Unit was up and running again.
+
+I knows these old tantalum caps are prone to fail, and I should
+probably change them all, but I don't have enough spare for now.
+
+After that, I could resume my adjustement procedure. And indeed there
+is an adjustment that allowed me to improve noticebly the brightness
+of the screen (the Intensity Cut-Off Level). Now I can run my HP3562A
+without the intensity knob FCW.
+
+
+Brief description
+-----------------
+
+.. image:: {filename}images/hp3562a/hp1345a_block_diagram.png
+
+.. image:: {filename}images/hp3562a/hp1345a_stroke_generator.png
+
+
+.. image:: {filename}images/hp3562a/hp1345a_ramp_generator.png
+
+
+.. image:: {filename}images/hp3562a/hp1345a_vector_processor.png
+
+.. image:: {filename}images/hp3562a/hp1345a_vpc_architecture.png
+
+
+