Troubleshooting DC Bias / PCU Issues

Have a channel shutdown? System logging indicate an issue with setting a DC level? Watch this video for guidance with DC bias / PCU issues.


Troubleshooting DC Bias / PCU Issues:

If you have had a channel shutdown and the system logging indicates an issue with setting a DC level, as seen here, the first step will be to determine if the device itself has failed.

There are a few different ways that can be accomplished.

First, you can remove the fixture containing the device in question from the system and perform a characterization test outside of the test stand on an external bench.

Second, you can utilize an integrated semiconductor parameter analyzer instrument in the system to perform a quick sweep and determine if the device is still functional.

Or, you can bias up the device manually in edit levels to see if the scenario is repeatable.

If any of these tests reveal that the device has experienced a failure, it can be replaced in the system with a fresh part to initialize a new test. If you have determined the device under test is still working as expected, that could point to an issue in the system or test fixture that must be addressed.

The first step down this path is to remove the device from the fixture being investigated. This removes any variables introduced by the device and simplifies the troubleshooting process.

With the device removed, open the Lifetest software and go to the edit level screen. This is where you can use the software to manually apply bias to the device in a controlled manner to rule out a variety of potential issues. Select the channel being investigated from the pulldown menu. In this instance, we will select channel three. What we'll do next is enable continuous update to get real time readouts of the measured DC levels.

Click set bias 2, followed by set bias 1. This will set the PCU pre-switch voltages for this channel, which are the internal power supply voltages. At this point, there is no voltage applied to the fixture. If this process returns any kind of error message and the power supply cannot set that internal voltage, this points to a potential hardware problem with the PCU for this channel. If you find yourself in this situation, it's a good time to initiate contact with Accel-RF and share your findings. Please zip up your system folder and log file, then upload those, along with any additional screenshots of error messages that you can provide.

Once you have set both bias 1 and bias 2 without an error occurring, enable the bias two on button. This will turn on bias 2 voltage to the empty fixture. A message box will pop up, just confirming that you're okay with turning on the power supply. Click okay. Check to make sure that the DUT voltage matches the pre-switch voltage. Also check to make sure there is no current flow, since this is an empty fixture and no current is expected. Make note of any errant values before moving on to the next step. If you see high current values here, or if you see that the DUT voltage didn't match the pre-switch voltage, both would be indicators of an issue. High current readings could point to a short somewhere in the fixture, for example.

Next, enable the bias 1 on button to turn on bias 1 voltage. Check the settings as you did before, to make sure pre-switches and DUT voltages match and there is no measured current. Now, grab a handheld DVM and measure up at the fixture to check what bias 1 and bias 2 voltages you measure. If you do find an unexpected result, that matches what originally caused your test to stop, that is a good sign that you're on the right path. Turn off the voltages to the fixture by clicking the DC on box. You'll see the indicators turn red and the measured DUT voltages disappear. The next step is to determine if the problem tracks with the fixture or with the channel in the system. The easiest way to do this is to exchange this fixture with another empty fixture installed in an available known working position. For example, let's say this is channel three. If channel four is available and not being used for tests, we could remove channel three, install it in the channel four slot, and vice versa. Move the channel four fixture into channel three.

After swapping the fixtures, repeat the steps that led to the unexpected result you found before. Did the problem move with the fixture to another position in the test stand, or did the result happen in the same channel with the second fixture? This is a good time to compile what you have found and send it to Accel-RF to review. This can include any screenshots of error messages that came up during your investigation, along with the standard files we request, including the system folder and the log file.

If you're still having issues, please SUBMIT A SUPPORT TICKET.