Re: TDS540B Power On Self Test Pass, but changing results from SPC


Siggi
 

On Wed, 31 Jan 2018 at 17:33 satbeginner <@satbeginner> wrote:

I read something about the attenuators being/getting iffy, or at least the
contact sheets in between the ceramic attenuators and the PCB.
I downloaded every piece of documentation I could find from Häkan's site
and everywhere else, but I did not yet find info about how to clean the
attenuator contact sheets.
Hey Leo,

a common problem with these scopes is that the relays on the attenuator
hybrids become high resistance or even open contact. You can see what the
attenuators look like here <
https://www.eevblog.com/forum/testgear/tektronix-tds520b-attenuator-swap/>,
and it's the cluster of four yellow relays that often fail. On my TDS784D
this caused SPC failures, but by measuring the relay contact resistance, I
was able to identify the culprits. After replacing them, my scope's worked
like clockwork ever since. The relays a readily available, I bought mine
from DigiKey, though I couldn't find the part number readily.
Be careful when you handle and reinstall the hybrids, it's easy to
mis-position them and to crack and destroy them on reinstallation.

Siggi

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