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What component is labeled SI (SI1, SI2, etc) on a PCB? By the way, what kind of capacitor is C7? (The one on the right of the "SI" component, assuming its a capacitor).

EDIT: The PCB is a combined boiler control board (Roca Victoria 20/20T) manufactured in Spain. The attached picture shows the components surrounding the spark igniter, whose transformer is the grey plastic box on the right.

The complete marking is "6W" "R600" "95" "0029". Measured with a leg detached from the PCB, it has no continuity (Tester displays "Open Loop") in both ways. "R600" suggests a 600-ohm resistor, but it's not. I tested the PCB operation with the component removed, and the spark igniter stops working, so it appears to be OK.

Thanks

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    \$\begingroup\$ Context often helps. Please edit your question to explain what the circuit is supposed to do. (It looks like a small SMPS.) Country of design may help too. \$\endgroup\$
    – Transistor
    Jul 16, 2019 at 16:07
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    \$\begingroup\$ Need to see the markings on the component \$\endgroup\$
    – Voltage Spike
    Jul 16, 2019 at 16:31
  • \$\begingroup\$ Could SI stand for "spark igniter"? (Not sure why it would apply to a small on-board component though) \$\endgroup\$
    – The Photon
    Jul 16, 2019 at 17:25
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    \$\begingroup\$ It's curious that the board was designed with the possibility of an SMD as an alternative. \$\endgroup\$ Jul 17, 2019 at 7:18

3 Answers 3

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It sounds like a SIDAC.

The small transformer and Q1 may generate several hundered volts which accumulates in one of the capacitors, when the SIDAC threshold is reached it begins conducting strongly dumping a pulse from the capacitor into the ignitor transformer.

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  • \$\begingroup\$ Excellent. I'd never heard of them. Littlefuse has a load of them. littelfuse.com/products/power-semiconductors/…. \$\endgroup\$
    – Transistor
    Jul 17, 2019 at 6:12
  • \$\begingroup\$ Don't the creepages look alarmingly narrow for a 600V working voltage, though? \$\endgroup\$ Jul 17, 2019 at 7:26
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    \$\begingroup\$ 600v is probbly wrong, they don't seem to make SIDACs for that voltage. 60 to 400 seems common. (deleted 600V) \$\endgroup\$
    – Jasen
    Jul 17, 2019 at 8:56
  • \$\begingroup\$ Thank you! You never stop learning new things. Next thing for me is to get a new SIDAC, and test if it works replacing the one placed in the PCB. That would be the definitive answer. By the way, any ideas regarding the type of C7? \$\endgroup\$
    – casanovg
    Jul 17, 2019 at 10:48
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    \$\begingroup\$ You should do that as a separate question as well. \$\endgroup\$ Jul 17, 2019 at 12:47
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The SI component designation is not listed in Wikipedia's Reference designator and not listed in this site's Standard nomenclature for component types. It's either non-standard or means something in Spanish.

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Figure 1. Forensic analysis.

The component is marked '0029'. If you detach one leg and bend the component up you may be able to read the rest of the markings. Update the question and we'll take it from there.

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  • \$\begingroup\$ That's correct, I checked the IEEE Std 315-1975 document and Wikipedia before posting, though with no luck. I'll post the exact marking later when I'm back at home. \$\endgroup\$
    – casanovg
    Jul 16, 2019 at 18:07
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    \$\begingroup\$ I'm not sure this really qualifies as an answer....? \$\endgroup\$
    – DerStrom8
    Jul 17, 2019 at 1:38
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use this information. its a sidac.

https://www.bristolwatch.com/ele/sidac.htm

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  • \$\begingroup\$ Amir Rashedi - Welcome :-) This is quite short for an answer here. It would help if you can Edit your answer and add details explaining why you believe this is the correct answer. Notice that the question already has an accepted answer, which gives some evidence for the identification as a SIDAC. If you only wanted to add that link as an extra source of information, then I can convert your answer to be a comment on that accepted answer (as you cannot write comments yourself yet). Thanks. \$\endgroup\$
    – SamGibson
    Mar 25, 2021 at 13:09

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