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Is there some kind of convention in electrical component maintenance that would explain a red marking on a capacitor?

I found this in my Pioneer SA 5300 audio amplifier and wondered if this carried some special meaning.

Pioneer marked capacitor connectors

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    \$\begingroup\$ It looks like QC marks to me. Someone in the QA department saying "Yes, I looked at that well enough to stake my next performance review on the statistical likeliness of this particular part failing." \$\endgroup\$
    – Ghedipunk
    Commented Jul 6, 2018 at 18:29
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    \$\begingroup\$ Seems more like a high voltage notifying or test point marks to me. \$\endgroup\$
    – rahulb
    Commented Jul 6, 2018 at 18:51
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    \$\begingroup\$ There is no way to know without asking the assembler \$\endgroup\$
    – Voltage Spike
    Commented Jul 6, 2018 at 19:23
  • \$\begingroup\$ @Ghedipunk if you could make that an answer I will accept it. Thanks! \$\endgroup\$ Commented Jul 6, 2018 at 19:26
  • \$\begingroup\$ the two solder joints below the three red marks look like they may be bad (cracked) .... give them a closer look \$\endgroup\$
    – jsotola
    Commented Jul 7, 2018 at 2:54

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Most likely Quality Assurance inspection.
For what purpose is anyone's guess (comments above are good guesses).... Here are some other ideas:

  • Such a large part as this could cause problems at or before the wave-soldering stage....an inspection to see that it is well-seated against the PCB after soldering.

  • A three-legged part with fat leads may miss a hole. An inspection to see that all three made it through their respective holes and bend over to make an acceptable mechanical seat.

  • An inspection to ensure that a polarized capacitor was inserted the right way, to save injury to the QA-person down the line who powers-it-up the first time.

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