Electronics > Repair
HP-8569 Spectrum Analyzer Repairs
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AF6LJ:
More work on the way, I have a bunch of Radio Club paper work I have to get done. I will be back ASAP.
AF6LJ:
Here is how to disassemble the bandwidth and frequency span switches.
I cannot stress the importance of proper tools.
A set of combination wrenches in imperial sizing.
Allen wrenches GOOD ONES! this is no place for cheap tools, some of the set screws are very tight and you don't want to have to drill them out and chase the threads with a tap.
Before I forget... the case screws are posidriv. not Phillips.
you will need a small pair of outside snap ring pliers for the reference level control group.
A copy of the service manual (volume 3)

With the proper tools, and a reasonable mechanical aptitude anybody, even someone partially sighted, like me can repair these switches.
Some operations may require not drinking that third cup of coffee. :)

The next post will contain pictures of the disassembly of the bandwidth and frequency span switches.

AF6LJ:

I reposted the above picture in order to show the back side of the bandwidth / span switch..\
The shaft can be seen in the center of the module just above the blue connector.


Turn the two switches ether full clockwise (engaged) or full counterclockwise this will establish a reference to make reassembly easier. After you do that make witness marks on the side of the switch rotors to document their position. (you will regret not doing this.)
I did go back and scratch in lines with an awol just in case the marker rubs off. Also notice the position of the two support pillars on the switch rotors. If you have a camera take loads of pictures if you have any question as to how things go back together you will have them...
Next post...
AF6LJ:


The wires connecting the sweep time board to the main switch board need to be un-soldered.
There are two screws holding the board to the top of the rear switch rotor, this rotor is the bandwidth rotor and has only one set of fingers.....



Here is a view of the bandwidth switch rotor, this one has its contact fingers intact. Take note of the spacers and washers under them. remove them and place all your parts up to this point in a safe place. I use Altoids boxes.
The screws used to remove the front panel assembly are in one. In another are all the hardware removed to disassemble the module. Now it is time to start one dedicated to this stage of the process.


Here is a view of the switch rotor removed. BE VERY CAREFUL OF THE BALL AND SPRING. These can get away from you if you are not careful.

You can see the spring and socket on the rotor where the ball resides when the switch rotor is installed on the shaft. Don't move anything just yet........
Take careful note of the pin protruding out of the side of the brass collar... and the location of the stop pin. This is where the grief can begin if you haven't documented their relationship to each other.
Next post............

AF6LJ:


Here you can see a small scratch I made to indicate which hole the pin is point to. This witness mark is needed to orientate the pin which engages bandwidth rotor when the knob is pushed in. That pin is what turns the bandwidth knob. Likewise you will find a similar pin on the frequency span rotor which will disengage when the knob is pushed in, leaving the frequency span knob in its current position.
It is now okay to remove the spacers, washers and the bandwidth switch detent, note the position of the notch.

Moving on...


On the other side there is an E clip and washer that needs to be removed.
I use an awol to remove the E clip, be careful not to loose this or the washer.

The shaft will not come out just yet, you have to loosen the two set screws holding the brass collar the stop pin is located in. Now the shaft will come out but be careful.
The frequency span switch detent must be supported while this shaft is removed. Use your hand to support the switch detent and screws, there is another ball and spring you must keep an eye on.


Take note of the spacers and washers. Also take note of the collar location, at the end of the hallow shaft. In this picture I am supporting the switch detent and screws with my hand while loosening the second set screw on the collar.

Next post......
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