Thank you for your quick response! Yes, I replaced C940,
but the closest I could source was a 1200uF Nichicon PW, which in the worst
case scenario could fall outside of the maximum specified tolerance of 1000uF
+ 30%. Mind you, I had to do pretty much the same for most of the other
capacitors, except all the other replacements fall within the original
tolerance bands: C954 47uF vs. 33uF; C956 390uF vs. 270uF; C960 etc. 1200uF
vs. 840uF; C942 & C943 15uF vs. 10uF.
I also have at the ready a
United Chemi-Con 100uF, 400V (could not source 450V) KXG series capacitor, so
I can easily replace C906. I got a bit of a cold feet syndrome since the KXG
is 1/4 the size of the Sprague cap, and I also read elsewhere that the Sprague
telephone grade caps last "forever". I found that last bit hard to believe
mind you, since it is an electrolytic after all. I could not find the ripple
current rating of the Sprague capacitor, but I'm guessing that the KXG will
work just fine. Maybe I should jus go ahead and replace C906?
wondering whether replacing the original 0.01uF 3000V caps with polypropylene
could have disrupted the power supply somehow? Or perhaps it could be the
overall collection of slightly higher than nominal capacitance on all the
output filter caps?
I realize that I am shotgunning the whole issue,
but I really did not mind replacing all the electrolytics. I have been doing
this for most of my other equipment at around 15 to 20 years of use as
preventative maintenance. Unfortunately I do not have access to an isolation
Thank you again,
--- In TekScopes@..., "Tom
> Hello Vaugha,
> I would replace C-906 as it is the main filter for the
> You can't really check the ripple on that cap without
an isolation transformer.
> Did you replace C-940? Without an
isolation transformer you are just shotgunning for the main problem.
Original Message -----
> From: Vaugha Brewchuk
> To: TekScopes@...
> Sent: Monday, May 23, 2011 11:05 AM
> Subject: [TekScopes] 2235
with 360 kHz 100mV P-P ringing on +100V PSU rail [1 Attachment]
> [Attachment(s) from Vaugha Brewchuk included
> Good day,
> This is my first post about
my first scope that I purchased recently. I am also not an electronics
technician, so please be gentle with me :-).
> The scope is in
excellent condition and has been recently calibrated. However, when using the
scope I noticed occasional small ripples in the traces. I opened the scope and
tested the power supplies and determined that the ripple on all the rails was
2 to 3 times larger than the limit quoted in the service manual. Consequently
I replaced all electrolytic capacitors in the power supply, except the C906
input filter capacitor, with Nichicon PW series capacitors. I used the exact
same capacity components where the originals were +/-20% and the next larger
capacity where the originals were -10% to +30, +50 or +100%. I also replaced
the four 0.01uF 3000V capacitors with CDE 940C30S1K-F polypropylene
> Unfortunately the occasional ripples have not
completely disappeared after the overhaul even though the traces seem to be a
bit sharper. The ripples on all the power supply rails have significantly
reduced, with the exception of the +100V rail. Here the actual low frequency
ripple seems to be in check at approximately 30mV P-P, but every second ripple
peak exhibits damped high frequency ringing at approximately 350 - 360kHz with
100mV P-P amplitude. I attached an image showing the ripple and the ringing on
the +100V rail.