I'm trying to fix a circuit from a waterboiler in my RV from 1982 (truma BO 128). It is responsible for opening the gas valve, creating sparks and monitoring the flame. The problem is that the voltage of the sparks is too low to jump the spark gap on the board.

I checked all condensators and diodes. They all seem to be fine. There are two components which I can't identify:

unidentified components

Both have three legs:

  • Component on the left: the diagonal legs are shorted. The other ones have 160 Ω resistance.
  • Component on the right: only the two left legs are connected on the board. They are shorted. On the top is the high voltage connection to the spark gap inside the burner. The legs on the bottom have 134 Ω resistance to the spark connection.

I'm also unsure what creates the high voltage. I would expect a transformer, but can't see anything like this.


board from side

reverse side

  • 3
    \$\begingroup\$ try to sharpen the spark tip; they round off over time, and the mating surface area has a huge effect on how well a spark forms; the smaller the better. \$\endgroup\$
    – dandavis
    Commented May 28, 2020 at 20:54
  • 1
    \$\begingroup\$ psychedelic traces \$\endgroup\$
    – DKNguyen
    Commented May 28, 2020 at 21:01
  • 1
    \$\begingroup\$ Groovy, man, groovy. \$\endgroup\$ Commented May 28, 2020 at 21:27
  • \$\begingroup\$ Did you find your answer? Was Jack's answer useful? Consider accepting it. And what were these components and/or cause of the device's failure? \$\endgroup\$ Commented Jul 3, 2020 at 11:46

1 Answer 1


The gray part should contain transformer and possibly a multiplier. HV transformer with voltage multiplier

It's encased in plastic and epoxy to avoid arching to PCB and between components.

You should be able to identify exact type, by measuring resistance between output and both input terminals in both polarities. Either way, listen for arching noises inside it when the spark should jump but doesn't. That's a clear sign it's failed.

As for the black component i can't answer.


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