54832B Passes ALL Self Tests but won't calibrate channel 4
Does anyone know what might cause this? Does anyone do a component level repair? I'm not going to pay Agilent $4000 for a board swap when it's possibly a few dollar component. Why don't they publish schematics of these things!!??
Imagine a cracked 0603 resistor causing this failure; less than a penny to fix if they would let us. Where's the C.L.I.P for this scope?
I can see a signal on the display for each channel.
What does it tell you if ALL self tests pass yet it can't complete calibration? I think the self tests need to be more robust.
Does anyone know what might cause this? Does anyone do a component level repair? I'm not going to pay Agilent $4000 for a board swap when it's possibly a few dollar component. Why don't they publish schematics of these things!!??
Imagine a cracked 0603 resistor causing this failure; less than a penny to fix if they would let us. Where's the C.L.I.P for this scope?
I can see a signal on the display for each channel.
What does it tell you if ALL self tests pass yet it can't complete calibration? I think the self tests need to be more robust.
I opened it up and I see signal heading out of the attenuator area toward the A/D module, and it even displays signal on the screen, I just can't pass CAL. Is there a separate signal path for CAL that the self test wouldn't check? I could really use some help.
The scope has a 32bit DAC that is used to generate accurate DC voltages. The scope vertical input has an 8bit DAC. When you run the self cal, you connect a cable from the rear panel AUX output to the channel inputs. Most of the cal is a vertical cal. This cal just programs the 32bit DAC to output specific DC voltages. That voltage is applied through the cable to the scope input. The internal cal software sets the attenuator to the correct settings and input impedance. The scope channel path measures that DC voltage. The internal cal software knows what voltage the 32bit DAC was programmed to generate and it compares the measure result with the actual programmed value and creates a software correction table for any differences. The performance tests are very similar except you use a power supply and set voltages using a voltmeter to generate the DC voltages. The last portion of the cal uses an AC signal for the trigger cal which just looks for crossing points of an AC signal.
The self tests are different because you are not using external cables for signal routing. The self tests use the offset DACs which are part of the channel path to create DC voltages. The offset voltages are less accurate than the 32bit DAC values and fewer DC values are checked. The trigger path is checked by moving the trigger level. The self tests are a smaller subset of tests than the self cal. The self tests are intended to be a quick check to make sure most of the acquisition system is working. The self tests do skip the scope front end because voltages are generated by the offset DACs and trigger level DAC.
Only channel 4 fails self cal. You did not say if the vertical or trigger failed. Both the vertical and trigger paths are checked in the self cal and they are listed separately in the cal results. If the vertical is failing, you could run the “To test single cursor measurement accuracy†from the testing performance section in the service manual. This would tell you which range is failing. If the performance test passes, then you might have a sticky attenuator contact on one of the attenuator ranges.
I am not aware of any CLIP packages for the 5483XX scopes. Most of the parts in the scope are purchased from external vendors to our specifications. The few custom boards in the scope are built by third party vendors and they stock all the parts. Any CLIPS would be just for those few custom boards and not the entire scope. We had CLIPs for older products, but there was such little customer interest that the time and money investment to create them just did not seem warranted. We switched to assembly level repair because it was not cost effective to have Agilent technicians spending hours trying to find that defective resistor or capacitor. Larger customers agreed that it made financial sense to them to replace modules instead of the time spent finding defective components. While all this make good business sense for Agilent, I can see how it does not help you out as the end user customer who would rather find that defective part instead of replacing an entire module.
I hope this answers your questions. But I am not sure if the answers will help you solve the problem with your scope.
What I would like to know is how can I see signal on that channel, but during cal, the scope cannot see signal?
You can try a few things.
Inspect the channel 4 BNC connector for obviously visible defects like a damage connector.
Check the input Z of channel 4 in both 1Mohn and 50 ohm. There is not spec on the 1Mohm setting, but you can compare to channels 1-3 to give you an idea of what to expect. The 50 ohm setting should be within about 5% of 50 ohms. It is possible that the 50 ohm setting might be open. If you read less than 50 ohms, the 50 ohm resistor could be changing value or dendrites might be growing under the relay that switches between 50 ohm and 1Mohm. If you suspect dendrites, removing the relay and cleaning the board could help.
Make sure you try the below at both 1Mohm and 50ohm settings.
Connect your signal to channel 4, then go through the attenuator ranges to check each volt/div setting. You are looking to see if one of the attenuator ranges does not work.
Cycle through the volt/dv ranges quickly. You are looking to see if one of the settings appears sticky by seeing a sluggish response.
Apply a small signal to the scope and move the front panel position (offset control) over the entire display at each volt/div setting. You are looking for an open range or a bad offset DAC.
Connect the AUX output to channel 4 (if not already connected). Go to the Utility\Calibration menu. In the upper left hand corner is a drop down menu for the AUX output. Choose DC from the drop down menu. This connects the same 32bit DAC that the self cal software uses to the AUX output. On each attenuator range, exercise the DC level over the entire range of the display.
Maybe an abnormality will give you a failure indication. I hope this helps you out.