I have looked through all the other 'what is this component' questions and have not found my component. I am looking for the component in the red box. It is from a rectifier circuit off a 1973 9.8 hp Mercury 110 Outboard. I ripped the silicon off the red plastic housing and this is what is underneath! I'm sure there is more than one person out there looking to source these parts.

Also I built the circuit in CircuitLab to see what it's like. The component in question is (F1).. you can see from the schematic it's a Bridge diode circuit. Right now the best guess on F1 is a fuse (I used to think it was a high wattage resistor - to drain transient current) If it's a Fuse, how is it being used successfully in this circuit? It doesn't seem to prevent any current from going to the output when blown.


simulate this circuit – Schematic created using CircuitLab

The circuit has two oscillating inputs like I believe the ignitor coils see when the EMF is passing through them. The switch to short them is while the coil is just left there - acting as a resistor of sorts. It is a magnento type ignition system where both the magnets and ignitor coils are positioned 180 degrees from each other, so that both magnets pass over the coils at the same time, creating a voltage in each coil to power the spark.

SW1 - is the high speed coil (~2K ohms)
SW2 - is the low speed coil (~4K ohms)

Can anybody tell me what the component in the red box is? It looks like straight carbon - like from a brushed motor but have not had any luck finding it through google or online part warehouses (digikey, mouser, etc..).

* I now believe this to be a Ceramic Cartridge fuse but need verification before assuming that is correct.

Thanks in advance!

1973 Mercury 110 9.8 Rectifier

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    \$\begingroup\$ So why would someone down vote this question? I need help that's why I came here.. Should I change something... I don't get it. Why would someone come to a site for questions and put the questions down instead of answering it or at least leave some feedback? \$\endgroup\$ – Treflip Nov 8 '14 at 23:23
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    \$\begingroup\$ That component in the box looks like a fuse to me, not a resistor. \$\endgroup\$ – RJR Nov 8 '14 at 23:38
  • \$\begingroup\$ Welcome, new user! I didn't downvote you, but I know the misterious user who did doesn't mean to be rude. It's that the first users of the site decided that questions about fixing electronic devices in which the poster didn't show good understanding of the design were off-topic here. So, your question does resemble a fix question, but can be also considered an "identify this component" (so you can fix the thing later). That's why the downvote I suppose. And here's a list of what on- and off-topic here \$\endgroup\$ – Ricardo Nov 8 '14 at 23:41
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    \$\begingroup\$ I believe that this question is relevant for this site. I don't see any reason why it should be migrated. Also along with the others I think that this is a fuse. \$\endgroup\$ – Adam Nov 9 '14 at 8:49
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    \$\begingroup\$ Looks more like a thermistor than a fuse, to me. Specifically, a "rod thermistor". (BTW there is no R2 on the schematic - did you re-label it F1?) A thermistor changes its resistance with temperature and may adjust the behaviour of this circuit with temperature (motor speed, power level). What would be the purpose of a fuse here? \$\endgroup\$ – Brian Drummond Nov 9 '14 at 11:39

The fuse F1 will protect V1 and V2 against SW1 and SW2 being closed simultaneously. Both switches closed together will cause a short circuit of the 2 voltage sources - depending on what these voltage sources are the current spike caused by a short circuit could be catastrophic.

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  • \$\begingroup\$ Thanks for the answer too! I added a little more detail on the magneto type ignition system to clarify. What you're saying is true, when both magnets pass over the ignitor coils (both switches are closed) at the same time current will flow through SW2 then SW1 (CW rotation) but this is the intended action to produce a spark later - the voltages add together. If the fuse was of great enough resistance then the current from SW1 would bypass going to ground and flow through Diode(D3) and out to Node1. Does this sound likely? \$\endgroup\$ – Treflip Nov 15 '14 at 12:36

It looks like a cheap, low resistance, high power, resistor (might be a thermistor). I recommend that you use a 5 ohm (or less), 10 watt, resistor as a replacement and measure the voltage drop across it and current to verify that 10 W is the appropriate power.

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  • \$\begingroup\$ Thanks for the answer! @BrianDrummond Thought this might be the case as well and I checked for resistance (see comments above) but can't get any recognizable measurement across it (including continuity - from one end to the broken end). Which makes it hard to see how it could be a fuse too. \$\endgroup\$ – Treflip Nov 15 '14 at 12:27

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