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I found this resistor on the control board of an old Whirlpool washing machine:

leak, side view

top view

Is that fluid leaking from the resistor? Why would that happen? Could it be something like stray epoxy or a chemical reaction with the substances in the machine like water vapor/soap instead?

If it is fluid or a chemical reaction, what implication does that have for the longevity/safety of the resistor?

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    \$\begingroup\$ Resistors contain no fluid. That's capacitors that leak like that. \$\endgroup\$
    – Hearth
    May 25, 2019 at 21:45
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    \$\begingroup\$ @Hearth I know. That's why it was so weird to see that. The deposit even has the sort of bubbly pattern that you get when chemicals mix after exiting an enclosure and then dry. \$\endgroup\$
    – Nonny Moose
    May 25, 2019 at 21:49
  • \$\begingroup\$ There's a slight chance that the resistor has overheated, causing the resin inside to bubble out. \$\endgroup\$
    – Hot Licks
    May 26, 2019 at 23:14
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    \$\begingroup\$ I mean, there are resistors with fluid. Just not the ones you find on PCBs. Some very old very large motors used primary resistance starters, with the resistors being an electrolyte bath with some big electrodes... \$\endgroup\$
    – SomeoneSomewhereSupportsMonica
    May 27, 2019 at 13:56
  • \$\begingroup\$ Does the washing machine function correctly? \$\endgroup\$
    – Scott Seidman
    Feb 8 at 22:45

4 Answers 4

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That's a cement block style, wirewound power resistor, sometimes called a square carbon power resistor. They look like this when new:

enter image description here

The one in your circuit board has been mounted upside-down from usual, so you can see the guts of it through the opening slot in the bottom, but that's no big deal.

Like all resistors, this component contains no fluid, so the material that has bubbled was added later. It looks very much like the amber conformal coating material that was popular for that vintage of PCB. It has probably been over-applied and ended up on the power resistor. Naturally it will bubble and discolour when heated. Apart from the odour and aesthetic factors, this is not in itself an electrical issue.

So I'd say with some confidence that there is very little concern about on-going chemical reactions.

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No, it's fine (as far as we can tell visually). Maybe some foam got melted onto it or a bit of glue was on there and was heated by the resistor. Those resistors have a ceramic housing, resistance wire winding around a core, and are held in by a type of ceramic cement. No liquids at all.

I wonder why they put the ugly side up. Whatever their reason, it's consistent, and if you search the PCB part number you'll find other examples with the burnt glue or whatever schmoo it is on there.

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    \$\begingroup\$ If they really did it on purpose, a hot spot forms on the "ugly side first because its not as good as a thermal insulator as the ceramic, so they might have done that so that the hot spot doesn't overheat the board under the resistor. \$\endgroup\$
    – drtechno
    May 26, 2019 at 14:08
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    \$\begingroup\$ There are some old ceramic block resistors that were not filled with ceramic but sand bonded with some sort of "glue". Not sure what happened when they got hot. \$\endgroup\$
    – Robert Endl
    May 26, 2019 at 19:49
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Ceramic resistors sometimes run pretty hot so something may have melted on it but my concern is to the right side of the yellow capacitors is visible corrosion that may be due to capacitor fluid leakage and may require replacement clean up may be possible with 97% alcohol

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  • \$\begingroup\$ Oh, wow. I definitely did not notice the real leakage! Thanks for pointing that out; I'll take a look at it. \$\endgroup\$
    – Nonny Moose
    May 26, 2019 at 19:30
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    \$\begingroup\$ @Elwin - That appears to be spider's web :-) \$\endgroup\$
    – Russell McMahon ♦
    May 26, 2019 at 21:00
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Here are some ceramic resistors inside an early 1990's guitar amp. Note the white caulk-like substance all around the resistors.

enter image description here

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  • \$\begingroup\$ Steve - Thanks for trying to help. However, Stack Exchange has different rules and etiquette than typical forums. You posted this as an answer, yet it does not specifically answer the original question i.e. "Is that fluid leaking from the resistor?" and the following related ones (even though an answer could be inferred from your post, that wouldn't be classed as an answer). Therefore your post is being flagged by other site members as "not an answer". Please can you edit your post ASAP to clearly answer the points in the original question, and therefore avoid it being deleted? Thanks. \$\endgroup\$
    – SamGibson ♦
    Feb 9 at 1:50

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