Capacitor value for C904 in various 22xx oscilloscopes


Tom Jobe <tomjobe@...>
 

Could anyone offer an opinion on this question?
In re-capping the power supply in a 2215A I've been working on, I ran into a little dilemma about the capacitance value of C904.
C904 is a line to line X2 capacitor that is installed immediately ahead of the full wave bridge that rectifies the incoming AC from the mains.
Some common 22xx scopes use a 2200 pF capacitor fro C904, and some of the later and/or more fully featured 22xx's use a .068 uF capacitor for C904.
That is 31 times more capacitance 'IF' I have my decimal points in the proper order, so I wonder what I should do?
I have both kinds of capacitors new and on hand, and I have been putting the .068 uF caps in place of the 2200 pF caps in these 22xx's without realizing what I was doing.
There have been no problems with using the higher capacitance C904's that I have seen, but then I have no real understanding of the circuitry and what it actually wants.
The application that really makes me wonder is the Commercial 2235 vs the Military 2235, these two scopes are very similar.
Yes, the Military 2235 does have graticule illumination that the Commercial 2235 does not have, but... 31 times more capacitance for C904?
Thank you!
tom jobe...

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