[Hps] ECal high-current preamps resolved

[Odian, Allen C.]

Hi Nathan,

Good job! I was wrong in blaming the capacitor.

Al
________________________________________
From: hps-bounces at jlab.org <hps-bounces at jlab.org> on behalf of Maurik Holtrop <maurik.holtrop at gmail.com>
Sent: Thursday, April 9, 2015 8:09 AM
To: Nathan Baltzell
Cc: HPS
Subject: Re: [Hps] ECal high-current preamps resolved

Hello Nathan, Emmanuel, Gabriel and Mathieu,

Excellent news and some good investigative work!

Thanks,
        Maurik


> On Apr 9, 2015, at 10:50 AM, Nathan Baltzell <baltzell at jlab.org> wrote:
>
> Hello Everyone,
>
> The cause of ECal's high-current HV groups has been found to be the glue of a label on the
> preamps' circuit boards.  Apparently it has become conductive over time, resulting in short
> circuiting the HV trace for some preamps.  Thanks to Emmanuel for diagnosing this with the
> “faulty” preamps we had replaced and sent home.
>
> This week, after only removing the labels, the current on our two existing high-current
> channels went down to zero.  Thanks to Gabriel and Mathieu, all 442 labels have been
> relocated and all channels retested with LEDs.
>
> This is important because, over the previous few months, we've seen a dozen preamps develop
> this problem and cause their entire group of 10 channels to draw tens of uA (some up to 100 uA,
> and vary significantly over time).  And since +10 uA results in a ~3% gain reduction unless voltages
> are manually adjusted, this is a big improvement for gain stability.
>
> -Nathan
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