Re: 2247A PSU Burn Mark near R2254/2255/2272/2273 and how to fix based on service manual


Darren Ting
 

Hi David 
You are absolutely right.  
After your advice, I recall after market change at the end of service manual and decided to look through it again and found exactly what we discuss about. It does not mention what problems they try to solve!
Plan to fix other changes as well. But exclude PNP transistor change which could be part spec changes.
I will focus changes involved increase resistors ohm and add in new resistors. Those likely solve overcurrent issues which could kill those IC.


Sent from Yahoo Mail on Android

On Tue, 15 Mar, 2016 at 5:48, David davidwhess@gmail.com [TekScopes]<TekScopes@yahoogroups.com> wrote:  
Ha! So there was a change notice from Tektronix addressing this exact
issue.

In the original design they must have figured that two 200 milliwatt
resistors in series for 400 milliwatts would be enough (and using
multiple parts is a fine way to distribute the heat load over a wider
area) but ultimately it was not and they changed it to one 1 watt
resistor.

On Mon, 14 Mar 2016 12:50:20 +0000 (UTC), you wrote:

Just in case members encounter this same issue.
Sample picture and fixes can be found in
https://groups.yahoo.com/neo/groups/TekScopes/files/2247A-PSU-BurnMark-Near-A18R2254%20/



[Non-text portions of this message have been removed]

Join TekScopes@groups.io to automatically receive all group messages.