Day 01 - Dismantling from bottom board

I am beginning the dismantling process of this scope.  Based on notes from last year, I am suspicious that CR1541 has failed.  I will not power up the scope

because I am not equipped to safely work with high voltages.  I need to remove the lower board in order to access the solder side of the board.  I have a soldering iron tinned with 60/40 tin lead solder that is specifically assigned to this project.

Figure 01-A:  Lower board with HV shield attached.  CR1541 is in the far upper right corner.

I removed the HV shield and replaced the screws in their respective holes.  I preserved the unique location of each screw.

Figure 01-B:  Lower board with HV shield removed.

After removing the HV shield, I removed dust using cotton
tipped applicators and then used the cotton to polish the capacitors and surrounding components.  I was careful to not apply fingerprints to the components which could otherwise affect conductivity across the exterior of the components.


In Figure 01-C, note the blue wire passing through the board.  Adjacent to this blue wire is a solder post secured by a machine screw/nut assembly.  This post also attaches a gray wire that goes to the 115/230 voltage selector switch.

Figure 01-C:  Note blue wire adjacent to machine nut.

In Figure 01-D, I de-soldered the blue and gray wire and replaced the post into it's mounting location.

Figure-01-D: The two wires are de-soldered and dislodged from board.

In Figure 01-E, the knobs for INTENSITY, FOCUS, SCALE ILLUM, POSITION and A TRIG HOLDOFF are loosened.  I carefully and fully seated a 1/16" hex driver in the hole and incremented pressure until the screw rotated.  The screws loosened without issue to allow the knobs to remove.

Figure 01-E: 1/16" hex driver used to loosen set screws

Note in Figure 01-F that the POSITION knob is unique on this scope and can adjust two dimensions.  There are two set screws on this assembly.

Figure 01-F:  Two set screws on this unique knob.

There are matching set screws on the variable components in Figure 01-G.  These set screws are loosened, the connecting rods removed and screws are re-tightened to to retain them from loss.  The documentation quotes "SETSCREW:4-40 X 0.188 INCH,HEX SOC STL" which provides the outer dimensions, but suggests nothing on the hex wrench needed.  A T5 Torx marginally did the job, this time."

Figure 01-G: Set screws of unknown dimension on variable components.

Day 00 - Background and examination.

April 28, 2020

The history

I acquired this oscilloscope at the Hunstville, AL hamfest for $40.  The seller assured my that it worked the day before, but I didn't believe him because if it was operational, it would have been much more expensive of a scope than $40.  I gave it some thought and thirty minutes later, I decided $40 was an acceptable price for a dead boat anchor.  If it actually worked, well, that would be a nice bonus.

The scope was dead on arrival, so I stored it away.  I powered it up and inspected it internally and discovered multiple power supply outputs were not operational.  I did not document the specific missing voltages.

As I needed to fly to Europe for an extended stay, I shelved the project for 6 months.

The Goal

To have an operational oscilloscope by remaining faithful to the design.

I intend to:

• Replace consumable or high risk components with modern equivalents that meet or exceed the original specifications.
• Maintain as much of the original design as possible.
• Perform a calibration to ensure the oscilloscope is able to perform within it's original standards.