LeCroy LC Series Oscilloscope PSU PS9611

[japlytic]

PROBLEM: Has trouble starting warm but will start cold; later on, it would not start even when cold (makes a ticking sound with the PSU fan running), even though the power supply did start with no external load when out of theoscilloscope.

FIX: Replacement of electrolytic capacitors (all low voltage - two 105C Chemi-Con KME and the rest being 85C Nichicon VX) on regulator control board nearest the auxiliary SMPS (all of the electrolytic capacitors on this board were around this area which were then replaced).
Also replaced two 85C Nichicon VX units near the external fan connector as a good measure.

The replacement electrolytic capacitors are all low-ESR units.

In switching power supplies, I would not recommend under any circumstances, 85C-rated electrolytic capacitors and I would also only recommend using low-ESR units in all sections, except for the primary (200/250V or 400-450V) units.

[Wester547]

Re: LeCroy LC Series Oscilloscope PSU PS9611

Were any of them bloated or leaking (from the bung)? Did they fail open or shorted (or partially open or shorted, IE leaky?)?

VX is a pretty old series (the radial through-hole version that is) so this Oscilloscope must have been fairly old and seen copious amounts of use. Mid to late 90s perhaps as far as date codes go?

I don't think 85C capacitors (Japanese) are that bad, if only because I've seen too many of them "tough it out" in very old CRT monitors with many hours on them and still measure in spec. These monitors ran fairly hot (usually, in my experience, before the capacitors fail in those, the flyback transformers or the horizontal output transistors go first). I'm in agreeance about low ESR capacitors being ideal for SMPS units, however.

[japlytic]

Re: LeCroy LC Series Oscilloscope PSU PS9611

Were any of them bloated or leaking (from the bung)? Did they fail open or shorted (or partially open or shorted, IE leaky?)?

None of them were leaking or bulging - some of them were quite small.