Intro: Agilent DSO7032A Oscilloscope - Repair of CAL PROTECT Switch
Eminently simple time-saving Instructable for a problem that exists because of ONE part that fails due to non-use over time.
This Agilent DSO7032A oscilloscope has a nice built-in self-calibration feature that must be manually configured using a small slide switch accessible through a slot on the upper rear of the device. Operating this switch must be done using a flat, narrow tool of your choice, like a screwdriver or even your car key.
Our units are approx. 8 years old and were quite expensive when purchased new. Factory repairs, as is well known, are typically quite expensive. Sending these units back to the factory to replace a SPDT switch that can be purchased online for no more than $3.50 just does not make sense. AND we had 8 out of 20 units with this same issue that prevents a self-calibration from occurring.
So a new Instructable was born!
Step 1: Tools & Parts Required
Long nose PLIERS
Straight blade screwdriver - 1/8" or so
Wrench (or Deep well Socket) - 7/16"
TORX screwdrivers / bits:
T20 (for nearly all the housing and internal shield screws)
T10 (for all the PC board screws)
T6 - for the 3 screws holding the front BNC jacks to the front panel
(Home Depot has a nice and affordable TORX multi-bit kit containing T3-T8 bits.
LOOK CLOSELY before you buy as this kit originally had only T5-T9. The NEW kit version has T3-T8.)
Soldering Iron / Station
Solder (63/37 flows better and at a lower temp)
Solder vacuum and/or desolder wick (both are nice to have)
(optional) Soldering Iron Tip Tinner and Cleaner
3 - small containers to hold hardware and parts that are removed
the Replacement Switch.
We chose to use an UPGRADED slide switch: C&K 110IM2S3CQE2, 6A, 120V, Digikey CKN5001-ND, $3.46
Step 2: FRONT PANEL - Remove the 3 Small T6 Screws by BNC Jacks
Remove the 3 small T6 screws by BNC jacks and place in holding container.
Step 3: REMOVE the 7 - T20 Screws Holding the BACK COVER in Place
Here are the locations of these 7 - T20 screws:
UPPER LEFT and RIGHT corners (2)
LOWER MIDDLE (1)
CARRY HANDLE (2)
LEG PIVOT SCREWS (2)
Step 4: REMOVAL of BACK COVER and INNER BACK SHIELD
In theory, the back cover should just lift vertically away easily.
BUT in reality you might have to "encourage" it a bit using a flat blade screwdriver to gently pry along the joint.
Once you have successfully removed the back cover it is time to REMOVE the 6 - T20 screws and the 2 - 7/16" hex nuts & washers.
The T20 screws are located:
Along the LONG edges (2 each)
Along the SHORT edges (1 each)
Place the T20 screws in the 2nd holding container.
NEXT, REMOVE the 2 - 7/16" hex nuts and washers holding the BNC jacks to the inner shield and then place them in the 2nd holding container.
USE EXTREME CARE ON THIS NEXT STEP
The inner back shield needs to be very carefully lifted near vertically to avoid breaking the plastic plunger associated with the ON-OFF SWITCH.
It may take some gentle prying with your flat blade screwdriver but it will detach.
BEFORE you attempt to completely lift this shield away, carefully raise it vertically for the purpose of repositioning the plunger mechanism AWAY from the main chassis. When you have adequate clearance, then tilt the shield away from you and begin assessing the internal wiring harnesses and how you need to "loosen" them in order to eventually gain full access to the main circuit board.
DISCONNECT 3 CABLES FROM MAIN BOARD & REMOVE SHIELD COMPLETELY
Disconnect the GRAY ribbon cable from the socket on the main board.
Disconnect the BLUE Molex connector with the BLACK & RED wires from the main board.
Disconnect the YELLOW Molex connector with WHITE wires from main board.
Remove the shield and place aside for now.
Step 5: REMOVAL of MAIN BOARD
It is now time to REMOVE the MAIN BOARD.
REMOVE the 7 T-10 screws (circled in YELLOW) and place in the 3rd holding container.
Pinch the 2 nylon STANDOFFS (GREEN arrows) with long-nose pliers so that they disengage from holding the main board and carefully lift the main board past the "lock" on each standoff. The main board can now be carefully flipped over to provide access to the 3 terminals of the faulty SPDT slide switch.
(Note: The main board is still "tethered" by a BLACK cable & a MULTI-COLOR cable, so use care in handling and positioning while preparing to desolder the old switch and then resolder the new switch.)
Step 6: DESOLDERING and REMOVAL of FAULTY SWITCH
Locate the 3 terminals of the faulty SPDT switch.
DESOLDER the 3 terminals using the solder vacuum. It may take multiple attempts to remove enough solder to begin the process of removing the switch from the main board. IF you are fortunate enough to have solder wick on-hand, this can expedite this part.
(Note to solder wick novices: Push the wick FIRMLY against the solder area and use your iron's tip to heat the wick. Capillary action should draw the molten solder away from the joint.)
When the 3 joints are reasonably clean, position your flat blade screwdriver between the switch and the main board and use it as a pry bar of sorts while you heat each terminal to assist in the final removal. Once the OLD switch has been detached, if you have solder wick, use it to perform final cleanup on each of the 3 holes by "pushing" the wick down into each hole with the tip of your soldering iron (conical tip is best) and let it wick away the remaining solder.
Now you are ready to INSTALL and RESOLDER the NEW SWITCH.
Step 7: INSTALL and RESOLDER the NEW SWITCH
CAUTION: Use care in the placement of the NEW SWITCH as to make sure that it is at a 90 degree placement in relation to the main board. This positioning is critical to this new switch lining up properly with the inner shield cover.
Suggestion: Solder only 1 terminal of the new switch to the main board. THEN, reposition the new switch while applying heat to that terminal in a way as to achieve the 90 degree placement. Once this has been successfully done, then solder the remaining 2 terminals of the switch.
Step 8: PUTTING THINGS BACK TOGETHER Prior to FINAL TESTING
Once the final soldering has been completed, then simply reverse the previous steps. Hopefully, you will have used the 3 holding containers. If so, the reassembly process will go quicker and easier.
SPECIAL CAUTION: When REASSEMBLING the INNER SHIELD be sure to position that shield over the front panel and carefully guide into place. What we are trying to PREVENT is a BROKEN SWITCH PLUNGER (see PHOTO) which could occur if you attempt to use a clam shell technique during reassembly.
Step 9: FINAL TESTING
OK. You are almost done.
FINAL TESTING of the self-calibration test requires 3 pieces of test equipment:
1 BNC "T" 2-way splitter
2 EQUAL LENGTH BNC cables
Turn on your Agilent DSO7032A oscilloscope and let it warm up for about 10 minutes prior to testing (this self-calibration test DETECTS if the unit is still warming up and will cause this test to FAIL if not at a stable temperature.)
Once your unit has warmed up, PRESS the UTILITY BUTTON on the FRONT PANEL.
That should display a MENU along the bottom of the screen.
CHOOSE the SERVICE soft key.
Then CHOOSE the START SELF TEST soft key.
Then OPERATE THE CAL PROTECT SWITCH that you just replaced and observe that the DISPLAY for that SWITCH changes from WHITE to GREEN AND that the SWITCH POSITION also tracks properly.
(Note: Should you want to test the remaining 39 keys & controls this is a good time to do that.)
PRESS the RUN/STOP BUTTON 3 times to EXIT this screen.
The previous MENU should now be displayed.
CONNECT each loose BNC cable end to each channel's INPUT and then connect the "T" 2-way Splitter to the TRIG OUT BNC jack on the upper rear of the back panel.
Make sure that the CAL PROTECT SWITCH is in the CAL UNPROTECTED position (UP).
CHOOSE the START USER CAL soft key.
For the next 7 minutes, the oscilloscope with then perform all the built-in self-tests.
When the self-tests are completed successfully, the screen will display the USER CAL PASSED message. All 20 of our units passed this test after switch replacement, so I am uncertain as to what any error message might look like.
YOU'RE NOW DONE!
There it is: One Instructable born of a need to provide what the manufacturer's website failed to provide to its many customers. Enjoy life, it is way too short!