r/AskElectronics • u/wasnt_me_rly • 2d ago

How can I find the appropriate replacement resistor when the original has blown off the board?

Post image

I'm looking to replace a resistor that looks to have overheated and disintegrated from the PCB. Per the repair manual, it is a 3.3k ohm SMD with +/- 5% tolerance. Size wise, the solder joints are ~1.2mm end to end (label R4125) which aligns to the length of the other resistors that are part of the circuit (label R4128 is 10k and R4127 is 5.6k.; both are ~1.2mm in length). This makes me believe these are 0402 sized resistor and per the repair manual, I know that these are NOT 1/10W SMDs.

Those are all of my knowns. Looking at DigiKey's filters, I need to guess at the:

  • Power (0.0189w to 0.25w)
  • Composition (Metal film, thick film, thin film)
  • Temperature Coefficient (+/-2ppm to +/-200ppm)
  • Features (Anti-sulfur, automotive, military, moisture resistant, pulse withstanding)

How would I go about selecting the values for the above 4 elements? Do any (beyond power) have a meaningful impact on the resistor? The application here would be for a Pioneer DJ CDJ2000 player (I posted some more details yesterday: https://www.reddit.com/r/AskElectronics/comments/1jqu1rz/looking_for_help_confirming_im_troubleshooting_a/). TIA!

2 Upvotes

75% Upvoted

4 comments sorted by

1

u/1310smf 2d ago edited 2d ago

More wattage is better, for the same case size, though if you haven't first solved whatever blew it off the board that might not help you. I see you had a spill you cleaned up.

What other characteristics matter would depend what it's doing in the circuit. First approximation, assume that consumer electronics would go with the least expensive option. I don't think any of those will matter for the select-by-different-resistance function you describe in the other post, so pick what costs you least (delivered - shipping is a bear with small electronics orders) that's in stock. Due to that I'll usually buy 10 if I need one or two as there's a volume discount (usually) and the shipping is most of the cost. And it means not buying another if one jumps out of the tweezers and gets lost.

I'd also check Newark and Mouser (at least) before placing an order.

2

u/wasnt_me_rly 2d ago

The circuit is meant to register button presses, but something spilled into one of the buttons, completing the circuit and keeping it permanently on. I'm guessing over time, the resistor overheated and blew. As such, I would guess any of the power handling is fine to handle the <1s button presses. While I'm not 100% sure, I think the circuit uses the 5V line for power.

1

u/riverturtle 1d ago

If it’s just for a button, then likely any resistor you pick with the right resistance will work. Composition etc don’t really matter. If it were me, I’d solder on an 1/8th watt through hole resistor and call it a day.

1

u/wasnt_me_rly 1d ago

Thanks. I ordered 3 different types just in case there are some unspecified requirements and will give this a go once they arrive.