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Just tried to troubleshoot the following pcb BMW MULF

I am checking the capacitors first, none of them have any marks of them so I'm using my multimeter to check their resistance. (I've checked online and found at least one site that says they can be tested by checking the resistance, however I found other sites that say they simply can't be tested using a standard multimeter.)

When reading the resistance of the top 4 capacitors, the leftmost three have the same reading; 18.73kΩ, however the last one reads 2.2kΩ. They all have the same markings on them, so I assumed the readings should be consistent.

Does this mean this capacitor needs replacing, or am I barking up the wrong tree?

Thanks.

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  • \$\begingroup\$ Did you discharge them before testing? \$\endgroup\$
    – Ignacio Vazquez-Abrams
    Mar 4, 2017 at 19:11
  • \$\begingroup\$ Not intentionally, online it advises to touch an insulated screwdriver to both prongs, but I can't access both connections with one screwdriver. \$\endgroup\$
    – cdsln
    Mar 4, 2017 at 19:14
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    \$\begingroup\$ None of them are part of a high-voltage or high-power power supply, so you can use an insulated wire to bridge the terminals. \$\endgroup\$
    – Ignacio Vazquez-Abrams
    Mar 4, 2017 at 19:16
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    \$\begingroup\$ Measuring the resistance of a capacitor rarely delivers useful information. Measuring resistance of parts in circuit rarely delivers useful information. \$\endgroup\$
    – JRE
    Mar 4, 2017 at 19:17
  • \$\begingroup\$ C & ESR of Caps requires a LCR meter not normally found in cheap DMM's \$\endgroup\$
    – Tony Stewart EE75
    Mar 4, 2017 at 19:34

1 Answer 1

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You can't reliably glean any information that way when IN circuit.

If they are all connected in parallel to the same circuit they will all measure the same anyway. e.g. decouplers.

If they are connected to different circuits you would have to factor in the resistance of the circuit. Even then, if it is not what you expect, you can not know if it is the capacitor or something else in the circuit.

With the capacitor in hand, or with one leg up, you can use a multi-meter to check for shorts or perhaps leakage in the capacitor, but that's about as far as that little meter will take you.

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  • \$\begingroup\$ I've also checked for continuity through the ICs and they are fine. Is there anything more I can do with just a multimeter? \$\endgroup\$
    – cdsln
    Mar 4, 2017 at 20:36
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    \$\begingroup\$ Other than measuring the powered up V & I... probably not. You can test resistors, but only in as far as the measured resistance can be no more than the expected resistor value. It could be lot less and be fine of course. \$\endgroup\$
    – Trevor_G
    Mar 4, 2017 at 20:42

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