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I am fixing the power supply board of a big mobile sound system. Skytec PA-200 - sadly I could not find any schematics or more information on it.

Unfortunately not only an electrolyte capacitor but also another part exploded which I couldn't safely identify. It may be a mov varistor and I would be very happy if one could safely identify what part it is and which specs it needs. Here you can see the exploded part (left) and the broken capacitor (right).

exploded part

Here is a diagram of the important parts of the circuit:

The broken/missing part is marked with the consumer icon. Furthermore a capacitor which broke aswell is marked on the right. I hope it is clear enough, otherwise I'm grateful for feedback to improve it.

circuit schematic

Here you can find an overall view of the circuit: circuit schematic

Based on burned parts found in the case it may be something similar to a ceramic part. burned part

The one component which looks the same is numbered with "104" and has in contrast to the capacitors, which look nearly the same, a half arrow above and a "R" in a circle.

similar component

The circuit supplies all internal parts with voltage and charges/uses the directly connected 12V battery.

Unfortunately I can not see the reason why the circuit broke, maybe because of a high air humidity in the environment it was last used.

It is still possible to use the sound system with a power cord connected to it. The power cord is directly connected to the transformer which is pictured in the schematic with the supply icon on the left side. So it may primarily be for using/loading the battery.

The question now is if it really is a varistor based on the additional information I provided and what kind of varistor do I need with which specs e.g. Joule.

And if it is the same component used in the other place on the board: How can I measure (with basic instruments) what type of -varistor?- it is or to get an approximation of the specs to use.

Thank you very much for your reply! If you need any more information feel free to ask.

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    \$\begingroup\$ Please trace the circuit around it. If close to the AC input I expect it to be a MOV (varistor). \$\endgroup\$
    – winny
    Commented Jul 22, 2021 at 21:00
  • \$\begingroup\$ Thank you for your answer! Your suggestion looks very promising. I updated the post with a schematic. Is it enough for you or should i draw more? \$\endgroup\$
    – Lonci
    Commented Jul 22, 2021 at 21:21
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    \$\begingroup\$ AS @winny states, it is likely a metal oxide varistor (MOV) , a component intended to absorb voltage surges. Ceramic capacitors rarely fail, though an MOV is much more likely to self destruct. You'll need the specs on the original to replace it - voltage ratings and energy absorption (in joules) vary greatly. \$\endgroup\$
    – DrMoishe Pippik
    Commented Jul 22, 2021 at 23:01
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    \$\begingroup\$ What's the reference designation of the part (should be printed on the board). Draw a real schematic, not lines on the board. Include how the transformer is connected. \$\endgroup\$
    – qrk
    Commented Jul 22, 2021 at 23:04
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    \$\begingroup\$ Any clues on the coincidence of failure, might be helpful. Lightning disturbances, on plugging in , during normal operation etc \$\endgroup\$
    – Tony Stewart EE75
    Commented Jul 22, 2021 at 23:22

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Based on an identical board, your exploded component is a ceramic capacitor marked 104 (100 nF).

capacitor

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  • \$\begingroup\$ Can you provide an explanation of how this answers the question \$\endgroup\$
    – Voltage Spike ♦
    Commented Nov 20, 2021 at 18:53
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    \$\begingroup\$ @VoltageSpike Apparently this is an identical PCB, so pfd provided a picture of an untoasted sample of the missing capacitor. However the explanation is very poor. \$\endgroup\$
    – Ariser
    Commented Nov 21, 2021 at 17:04
  • \$\begingroup\$ But is explanation really necessary in this case? poor or otherwise... what would be really interesting is the cause. because if there is something else wrong with the board, replacing component may just end up with another exploded part \$\endgroup\$
    – Maple
    Commented Dec 28, 2021 at 4:28

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