Re: 2465B Replace Aluminum Electrolytics with Tantalum

Leon Robinson
 

Lets see that would make me 107 Years Young.
Sounds like you did a good job. Leon Robinson    K5JLR

Political Correctness is a Political Disease.

From: machineguy59 via Groups.Io <machineguy59=yahoo.com@groups.io>
To: TekScopes@groups.io
Sent: Saturday, August 11, 2018 3:28 PM
Subject: [TekScopes] 2465B Replace Aluminum Electrolytics with Tantalum

See this photo album https://groups.io/g/TekScopes/album?id=66462 for my recent repairs on a 2465B.  This 2465B had modest corrosion on the A5 board from leaking aluminum electrolytic capacitors.  On this board the pads for C2222 and C2520 were partially eaten away and R2013 itself had failed completely (R2013 pads were OK).  A few cycles of applying flux, hot air heating, then wash with PCB cleaner and the board was ready for repair.  But I wanted a repair that did not suffer the same fate as the OEM assembly.

Todays aluminum electrolytic capacitors have more robust seals than the ones Tek had available in the 1990's.  Also, hand soldering the capacitors to the board avoids severely heating the capacitor seals as happens with wave soldering systems.  Still, electrolytic capacitors always eventually fail and often leak electrolyte onto the PCB.  Tantalum electrolytics do not have this failure mode, at least not often, because they are made different.  So I resolved to replace the four aluminum electrolytic capacitors with SMD tantalum electrolytic capacitors.  I understand that Tektronix did something like that with certain 2465B scopes manufactured in Guernsey, UK (see here https://groups.io/g/TekScopes/photo/12841/0?p=Name,,,20,1,0,0 ).

So I elongated one pad of each mounting for C2011, C2113, C2331, and C2965.  This was simple to do.  Each of these capacitors have a through hole or trace on one pad that can be cleaned and a copper foil strip can be soldered to elongate that pad by 1 to 2 mm (I was neat, not precise).  This allowed me to hand solder 2917 package size SMD capacitors.  I chose 4:1 or better voltage derating and an ESR of less than 1 Ohm in each case.  The result is working very well.  I will try to report back in 30 years on how the reliability turned out.

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