(Topic ID: 259505)

Stern Lightning resistor burning


By Nihonmasa

37 days ago



Topic Stats

  • 5 posts
  • 2 Pinsiders participating
  • Latest reply 36 days ago by Quench
  • No one calls this topic a favorite

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#1 37 days ago

Hi there,

Still working on my Lightning; having an issue here:
The knocker coil was seized; changed it. (N 26 1200 replaced by a J26 1200).
As it did not fire I changed the assoiciated transistor (Q3) which was clearly dead => it now burns the associated resistor (R16) each time it fires.
Any idea of what may cause this?

R16 is a 330 Ohm resistor; the new transistor is the exact same as the previous one )stole it from an unused one); tried with 2 transistors and had the same results.

Thanks in advance for any help!

#2 37 days ago

More info: now burning on every start-up. Tried with another coil; same stuff. Diodes were ok.

Does anyone have a pic of the wiring of the knocker to make sure I did not screw it up?
But if it's not that, I am lost

edit: game on, even with the burnt transistor, when doing the test "center tab of Q3 to ground" => knocker works.
So I guess my wiring and the transistor and diodes are ok? Any idea?

edit: CR3 tested good but still changed it with a 1n4004 => same stuff

#3 36 days ago
Quoted from Nihonmasa:

game on, even with the burnt transistor, when doing the test "center tab of Q3 to ground" => knocker works.
So I guess my wiring and the transistor and diodes are ok? Any idea?

Grounding the metal tab of Q3 only tells you if the wiring from the transistor to the coil is good. It does
not
tell you the transistor or diode are good.

Quoted from Nihonmasa:

As it did not fire I changed the assoiciated transistor (Q3) which was clearly dead => it now burns the associated resistor (R16) each time it fires.

The only way resistor R16 can burn is if it is receiving 43 volts from the knocker coil due to a short circuit in the Q3 transistor between the base and collector legs, or capacitor C17 is shorted.

You sure the replacement Q3 is the correct type (what model is it?) and installed the right way around?

#4 36 days ago

Hi Quench,

thanks for the clarifications!
Q3 replacement is fine, as I got it from the same board, from an unused circuit (Q11, Q12, Q16,Q17 and Q19 are unused with Lightning) and as I tested 3 differents ones from those circuits.
C17 was already changed as well (forgot to edit here) with the same result.

I did another test which worked => I tried again (after replacing another burnt resistor ) with another knocker from my Stern Dracula => working just fine.

So the conclusion seems to be that a J-26-1200 is not a proper replacement coil for a N-26-1200; I am going to order a new one.

#5 36 days ago

J-26-1200 and N-26-1200 coils have the same electrical characteristics - 26 gauge wire wound 1200 times.
The difference is only the plastic bobbin they are wound on, from memory the N coil is a little shorter and has square ends.
The J-26-1200 coil should not have been the cause of R16 burning unless the coil lugs were shorting on the metal assembly or maybe if your J-26-1200 was missing the diode across the lugs and it was blowing the transistor.
The resistance of these coils is about 11 ohms from memory.

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