# Is my QA403 Broken?

**URL:** <https://forum.quantasylum.com/t/is-my-qa403-broken/2181>\
**Category:** Uncategorized\
**Created:** [January 28, 2026, 3:07pm UTC](https://forum.quantasylum.com/t/is-my-qa403-broken/2181 "2026-01-28T15:07:18Z")\
**Posts on this page:** 4\
**Page:** 1

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**Author:** ![Bimmer](https://avatars.discourse-cdn.com/v4/letter/b/db5fbb/32.png) [@Bimmer](https://forum.quantasylum.com/u/Bimmer)\
**Post date:** [January 28, 2026, 3:07pm UTC](https://forum.quantasylum.com/t/is-my-qa403-broken/2181/1 "2026-01-28T15:07:18Z")

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Hello Forum

Last week, during the regular day work, something happend to the QA403. Looks like the inputs and outputs are disconnected and the hardware is generating 150Hz signal and mearusing itself only on right channel. Left channel has the same signal but -50dBV lower than the right channel.

 ![image](https://canada1.discourse-cdn.com/flex032/uploads/quantasylum/original/2X/b/bda7a802f5a2f4793f98f353532c1b350191860c.png)

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**Author:** ![matt](https://avatars.discourse-cdn.com/v4/letter/m/a6a055/32.png) [@matt](https://forum.quantasylum.com/u/matt)\
**Post date:** [January 28, 2026, 8:27pm UTC](https://forum.quantasylum.com/t/is-my-qa403-broken/2181/2 "2026-01-28T20:27:10Z")

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Hi @Bimmer, can you please try to replicate some of the plots from the page here? It looks like your inputs are picking up 60 Hz via the unterminated 100k input impedance. If you short all the inputs, what does it look like?

> **[Verifying Calibration Manually](https://github.com/QuantAsylum/QA40x/wiki/Verifying-Calibration-Manually)**
>
> Releases (no source) for the QA402 and QA403 Audio Analyzer. - QuantAsylum/QA40x

For the unit on my desk, if I do:

1. File-\>New
2. 0 dBV full scale input
3. Increase FFT to 32K
4. Increase averaging to 10
5. Press RMS button to add RMS measurement tiles
6. Short all 4 inputs
7. Run.

In the plot below, you see there’s no 60 Hz, and RMS is better than -115 dBV.

 ![image](https://canada1.discourse-cdn.com/flex032/uploads/quantasylum/original/2X/a/a56f2fd9c1e1b15bf378cf682a68a4cfeb6b48d9.png)

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**Author:** ![Bimmer](https://avatars.discourse-cdn.com/v4/letter/b/db5fbb/32.png) [@Bimmer](https://forum.quantasylum.com/u/Bimmer)\
**Post date:** [January 29, 2026, 12:34pm UTC](https://forum.quantasylum.com/t/is-my-qa403-broken/2181/3 "2026-01-29T12:34:47Z")

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Hello Matt

I ve made the full procedure you mentioned, but nothing has changed.

Please see the picture. All inputs are shorted.

Looks like the is no reaction at the inputs.

 ![image](https://canada1.discourse-cdn.com/flex032/uploads/quantasylum/original/2X/f/fe8aa3b0a12eef7f2767d200bc7159da72e254d3.png)

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**Author:** ![matt](https://avatars.discourse-cdn.com/v4/letter/m/a6a055/32.png) [@matt](https://forum.quantasylum.com/u/matt)\
**Post date:** [January 29, 2026, 2:39pm UTC](https://forum.quantasylum.com/t/is-my-qa403-broken/2181/4 "2026-01-29T14:39:16Z")

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Hi @Bimmer, I think this will need to be sent in. I just replied to what I think is you in the support email. Let me know if not. Thanks!