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#1
11-15-2020, 02:56 PM
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Need help identifying components on Tachometer board
Pulled my non working tachometer amp. Smelled magic smoke and dug deeper.
Can anyone tell me what this burt part is?  Sent from my iPhone using Tapatalk
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Current: 16 E400 4Matic 91 300E 4Matic - 2nd car 83 300D Past: 06 E350 4Matic 87 190E 2.6 - 1st car Last edited by m5mulli; 11-15-2020 at 05:03 PM. 
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#3
11-16-2020, 10:30 AM
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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.
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1984 & 1985 CA 300D's 1964 & 65 Mopar's - Valiant, Dart, Newport 1996 & 2002 Chrysler minivans
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#4
11-16-2020, 10:44 AM
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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... Sent from my iPhone using Tapatalk
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Current: 16 E400 4Matic 91 300E 4Matic - 2nd car 83 300D Past: 06 E350 4Matic 87 190E 2.6 - 1st car
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#5
11-18-2020, 01:41 PM
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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 Sent from my iPhone using Tapatalk
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Current: 16 E400 4Matic 91 300E 4Matic - 2nd car 83 300D Past: 06 E350 4Matic 87 190E 2.6 - 1st car
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