--- title: AlcoTest, Density Meter, Refractometer, or Polarimeter Boot up Issue description: Troubleshoot an AlcoTest booting issue when the display flickers or the unit repeatedly cycles during startup. Learn how to identify a failing power supply and restore normal operation. --- [Skip to content](https://knowledge.rudolphresearch.com/alcotest-boot-up-issue#main-content) English Show submenu for translations ![RRA\_Logo\_For\_email.png\]](https://knowledge.rudolphresearch.com/hs-fs/hubfs/RRA_Logo_For_email.png?height=50&name=RRA_Logo_For_email.png) Open main navigation Close main navigation - English Show submenu for translations - [Go to rudolphresearch.com](https://rudolphresearch.com/) [Go to rudolphresearch.com](https://rudolphresearch.com/) Hello. How can we help you? - There are no suggestions because the search field is empty. 1. [Ask Professor Rudy](https://knowledge.rudolphresearch.com/?hsLang=en) 2. [Troubleshooting](https://knowledge.rudolphresearch.com/troubleshooting?hsLang=en) 3. [Troubleshooting - Boot Up Issue](https://knowledge.rudolphresearch.com/troubleshooting?hsLang=en#troubleshooting-boot-up-issue) # AlcoTest, Density Meter, Refractometer, or Polarimeter Boot up Issue ## Booting Issue Troubleshooting | Power Supply Replacement ### Summary If an instrument does not boot correctly, the display flickers, or the unit repeatedly cycles during power-up, the issue may be related to the external power supply. This article explains how to identify the symptom and when to replace the power supply. #### Overview If your instrument powers on but does not complete startup, you may observe one or more of the following symptoms: - The instrument does not boot normally - The display flickers during startup - The unit beeps while the display flickers - The system repeatedly cycles after power is applied - The LED on the AC power supply is illuminated, but the instrument remains unstable In cases like this, the root cause may be a failing power supply rather than an internal instrument fault. #### Symptoms - “The unit failed to boot.” - “The display flickers.” - “The system cycles about once per second after power is applied.” - “The light is green, but it flickers when the unit beeps.” #### Likely cause A failing or unstable power supply can prevent the instrument from completing its startup sequence. When the supplied voltage is inconsistent, the instrument may flicker, beep, or restart repeatedly. #### Recommended action 1. Confirm that the power supply is connected securely. 2. Check whether the power supply LED is steady or blinking. 3. Observe whether the instrument display flickers or cycles during startup. 4. If these symptoms persist, replace the power supply with the correct approved replacement. 5. Restart the instrument after installing the replacement power supply. #### Resolution If the power supply is the source of the problem, replacing it should restore normal startup behavior. After replacement, verify that: - The instrument powers on normally - The display remains stable - The startup sequence completes without repeated cycling - Normal operation resumes #### When to contact support Contact Rudolph Research Analytical Technical Support if: - The replacement power supply does not resolve the issue - The display remains unstable - The instrument still fails to boot - Additional error symptoms appear after startup --- ![Power Flowchart](https://knowledge.rudolphresearch.com/hs-fs/hubfs/Power%20Flowchart.png?width=670&height=1005&name=Power%20Flowchart.png)     ---   **Need Additional Help?** Give us a call, we are happy to help! (973) 584-1558  Monday - Friday 8:30AM - 5PM EST or [open a service ticket](https://rudolphresearch.com/resources/service/contact-service/). 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