Need help identifying components on Tachometer board

[m5mulli]

Pulled my non working tachometer amp. Smelled magic smoke and dug deeper.

Can anyone tell me what this burt part is?




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[m5mulli]

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[BillGrissom]

I have seen precision wire-wound resistors which are in a package with end caps like that. They are usually coated with plastic, which likely burnt away. But, various 2-lead devices (resistor, inductor, capacitor, ...) might use the same "packaging". At least that is true of 3-lead devices (IGBT, MOSFET, Vreg, ...). See if you can measure a resistance, with it out of the circuit. A wirewound resistor might have overheated, but not been damaged.

[m5mulli]

It’s burned through. I found a circuit diagram yesterday and it looks like it is a 33ohm resistor that is directly off the 12v input pin.


I don’t exactly know the current draw so I ordered a few sets of resistors with different wattage ratings.

We will see...


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[m5mulli]

Well. Resistor has been replaced but that still didn’t help. While I had things appart I decided to check the output voltage from pin 3 with the amp installed and the engine idling. It’s outputting about 400-500mv and goes up as I rev the engine. So that’s a good sign but I am not sure if those ranges are correct.

I guess the next thing is to pull the instrument cluster and see if the tach is even connected


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