Capacitor Failure Symptoms: Difference between revisions
Rewrite with full citations (Nichicon CAT.8101H hosted here, Vishay 40110, KEMET F3011): corrected 60 Hz hum to twice mains frequency, corrected bulging mechanism to Nichicon gas generation, added missing film/X2 suppression section, added tantalum derating 60-50 percent, added Class II ceramic DC-bias behaviour, replaced Japanese-brand rule with no-datasheet-no-purchase, replaced IPA-only cleanup with Nichicon soap-and-water plus never acidic/alkaline, replaced reforming folklore with Nichic... |
P4 verification: add worked examples of ESR-rise and RIFA failure from the two hosted Pina books, with the U.S./International designator warning |
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== Replacing capacitors == | == Replacing capacitors == | ||
* '''Voltage rating: match or exceed the original.''' A rating at or below the rail the part sits on is always wrong | * '''Voltage rating: match or exceed the original.''' A rating at or below the rail the part sits on is always wrong, and it damages machines. | ||
* '''105 °C parts in power supplies.''' Life follows the Arrhenius relationship — Nichicon states that life doubles for every 10 °C drop in temperature.<ref name="nichicon" /> A 105 °C part in place of an 85 °C part of the same endurance rating is a real, calculable gain, not a superstition. | * '''105 °C parts in power supplies.''' Life follows the Arrhenius relationship — Nichicon states that life doubles for every 10 °C drop in temperature.<ref name="nichicon" /> A 105 °C part in place of an 85 °C part of the same endurance rating is a real, calculable gain, not a superstition. | ||
* '''Match ESR and ripple rating, not just µF and volts.''' A switch-mode supply designed around a low-ESR part will misbehave with a general-purpose one. Exceeding the ripple rating is one of Nichicon's listed causes of capacitance loss and rising ESR.<ref name="nichicon" /> | * '''Match ESR and ripple rating, not just µF and volts.''' A switch-mode supply designed around a low-ESR part will misbehave with a general-purpose one. Exceeding the ripple rating is one of Nichicon's listed causes of capacitance loss and rising ESR.<ref name="nichicon" /> | ||
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* Occasionally switching a machine on is not a re-forming procedure and does not follow the guidance above. | * Occasionally switching a machine on is not a re-forming procedure and does not follow the guidance above. | ||
* Storage conditions are worth getting right: Nichicon recommends 5 °C to 35 °C and 75 % relative humidity or less, out of direct sunlight.<ref name="nichicon" /> | * Storage conditions are worth getting right: Nichicon recommends 5 °C to 35 °C and 75 % relative humidity or less, out of direct sunlight.<ref name="nichicon" /> | ||
== Worked examples from documents held here == | |||
Two hosted books give named-component examples of the failure modes described above, both for the | |||
compact Macintosh analogue board. | |||
* '''C1, the horizontal-sweep capacitor.''' Larry Pina records it as a 3.9 µF '''non-polarised''' | |||
part and recommends a higher-voltage non-polarised replacement to stop the fault recurring; the | |||
failure sequence is poor horizontal linearity, then bright diagonal lines a few minutes after | |||
switch-on, then a darkening display and smoke. This is ESR rise under high-frequency current in a | |||
case with no fan, and it is the clearest worked example of the mechanism on this | |||
wiki.<ref name="capdms">Larry Pina, ''The Dead Mac Scrolls'', 1992, ISBN 0-940235-25-0, hosted here | |||
as [[The Dead Mac Scrolls]]; and ''Macintosh Repair & Upgrade Secrets'', 1990, hosted here as | |||
[[Macintosh Repair & Upgrade Secrets]], chapter 5 "Video Problems". Secondary sources.</ref> | |||
* '''RIFA suppression capacitors.''' Pina's parts lists identify the "molded minibox, Rifa" positions | |||
on both the U.S. and the International Macintosh analogue boards — 4700 pF 250 V and 0.1–0.47 µF | |||
250 V — which are the mains-rated film parts that crack, smoke and smell. His lists also give the | |||
'''100 µF 200 V''' mains-side electrolytics on the same boards, which is the rating to match or | |||
exceed.<ref name="capdms" /> | |||
'''Read the right list.''' Those two boards use '''the same reference designators for different | |||
components''': C13 is a 33 µF 16 V electrolytic on the U.S. board and a 0.01 µF 1.5 kV ceramic disc | |||
on the International one. See | |||
[[Macintosh 128K/512K Capacitor Replacement Guide]].<ref name="capdms" /> | |||
== Related pages == | == Related pages == | ||