content/TeK2445.rst

==================================
 Tektronics 2445 scope PSU repair
==================================

:Author: David Douard
:Category: Electronics
:Tags: Tektronics, 2445, analog scope, repair, test equipment

I've recently took my good old Tek 2445 scope from the cellar
(along with my {tag}HP8904A signal generator), and it showed signs of
tired PSU: unstable display, noise, then the typical noise of a
capacitor failure.

Here is the beast:

.. image:: {filename}images/tek2445/tek2445.jpg
   :alt: My old Tektronics 2445 scope
      
And some pictures of its womb:

.. image:: {filename}images/tek2445/tek2445_A1.jpg
   :alt: The main analog board.
	   
.. image:: {filename}images/tek2445/tek2445_top.jpg
   :alt: Top view of the scope.

The PSU consists in two PCBs coupled with long jumpers. It's not very
difficult to disassemble them but not that straighforard either. I've
seen easier test equipments to take apart.

Whatever, its problem was a classic failure of several X2 and Y
capacitors on the regulator board (A2):

.. image:: {filename}images/tek2445/PSU_A2.png
   :alt: The regulator board os the PSU.

.. image:: {filename}images/tek2445/board_a2.jpg
   :alt: The regulator board os the PSU.
	 
.. image:: {filename}images/tek2445/board_a2_C1018.jpg
   :alt: Dead C1018 capacitor.
	 

and the inverter board (A3), mainly C1020, C1051 and C1052:

.. image:: {filename}images/tek2445/PSU_A3.png
   :alt: The inverter board of the PSU.

	 
For now, I've replaced them with parts from old switching power
supplies (from old Dell and IBM computers), but I'd rather replace
them with brand new components. I also still have some small display
instabilities, which I need to investigate a bit more. I'll probably
replace most of the electrolytics caps on the PSU so that I won't have
to repair again any time soon (famous last words).