> For the complete documentation index, see [llms.txt](https://knowledge.illumina.com/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://knowledge.illumina.com/instrumentation/nextseq-1000-2000/instrumentation-nextseq-1000-2000-troubleshooting-list/000007095.md).
# Troubleshooting NextSeq 1000/2000 low read 1 intensity
NextSeq 1000/2000 run with low intensities on Read 1 and Index 1 which then recovers for Index 2 and Read 2 are typically caused by issues with poor priming Read 1 and Index 1.
Issues with priming can be caused by the following root causes:
* Library design or custom primers.
* Custom primer not proper loaded into the reagent cartridge when needed.
* Reagent cartridge consumable quality.
**Diagnosing**
The Intensity Data by Cycle charts will show drops at the start of Read 1 and/or Index 1.
**Troubleshooting steps:**
* Review library design, custom primers and where custom primer loaded, if applicable.
* If run meets yield and Q30 specification, proceed with downstream analysis of the run.
* See [S](https://www.illumina.com/systems/sequencing-platforms/nextseq-1000-2000/specifications.html)[pecifications for the NextSeq 1000/2000](https://www.illumina.com/systems/sequencing-platforms/nextseq-1000-2000/specifications.html).
* If run does not meet yield and Q30 specification and run setup has been ruled out, contact [Illumina Technical Support](https://www.illumina.com/company/contact-us.html#/united-states/technical-support) for the next steps.
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| *For any feedback or questions regarding this article (Illumina Knowledge Article #7095), contact Illumina Technical Support* [*techsupport@illumina.com*](mailto:techsupport@illumina.com?subject=Question%2FFeedback%20Regarding%20Illumina%20Knowledge%20Article%20#000007095%20-%20Instrumentation%20\&body=Dear%20Illumina%20Technical%20Support,%0D%0A%0D%0A)*.* |
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