Rode NT4 Repair

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Update ...

The bad news: Rode doesn't want anyone working on these. I called them about perhaps buying some parts, and the support rep told me that, since they're so hard to work on, they don't offer any parts for sale (he also said that's why they give a 10-yr warranty for this mic, which unfortunately doesn't help me).

But ... just for anyone who ever wants to work on one of these, a little info, because I really had a hard time finding anything online. To disassemble, unscrew the bottom part of the body. Then turn the little flathead screw at the base fully clockwise, which allows you to pull out the 5-pin connector and get at the connections. Then unscrew the ring near the top of the body (if you're looking at the front of the mic, turn it to the RIGHT). This allows you to separate the top part of the body, at least as far as the slack of the wires to the capsules will allow.

You can then desolder the wires from the 5-pin connector, and slide the plastic inner assembly, which holds the PCB, UP and out. The PCB just rests on little pegs on the plastic, so it will just lift off and then you can get to everything on the PCB.

If you need to get to the capsule wiring, there are two phillips-head screws at the top-inside of the top part of the body. If you unscrew those, you'll have a much easier time moving the wires that go to the capsules. It's a very small passageway that they go through.

Hope that helps someone. And now, a question: The PCB on this one was corroded to hell, so I cleaned everything very thoroughly. Between that and cleaning some corrosion out of the capsule connections, I was able to get the mic passing signal again. However, one channel sounds perfect, but the other has a faint but audible high-frequency whine. Any idea what could cause this?

I've swapped channels to make sure it's not the cable, interface, etc. I've also swapped capsules, and the whine remains on the same channel, so it's not related to the capsule. Interestingly, it also remains if I turn the phantom power off.

Any advice highly appreciated -- thanks!!



 
ln76d said:
Post pictures of PCB both sides.

Hey ln76d, sorry for the delay, life got in the way for a while.

But finally got back to the mic and took it apart again to take some pics. Here are the links. Any clue what might make this slight whine in one channel and not the other?

I can rule out the capsule because when I swap them the same channel makes the same noise. But aside from that, I have no clue what it could be. As you can see, there is still a little corrosion that I haven't been able to get off. If you think that might be an issue, I can try to just keep scrubbing away at it. Or is there a component in particular that might cause the whine?

Thanks so much for any thoughts!!

https://goo.gl/photos/8GViQQt7gEZexxGEA

https://goo.gl/photos/RjBnfFXvSwPZwrCPA

https://goo.gl/photos/CEV8cP1CckhDCReE8

https://goo.gl/photos/sXuJYt9mZoJyHPbeA


 
Two additional notes, in case it helps:

1) The frequency of the whine is around 5-6k

2) It happens whether the mic is switched on or off

Anyone have any thoughts what could cause this?
 
I would check first (multimeter) all the diodes - especially D1 - D4. You could check by occasion ecoupling capacitors.
IF you will not find anything - check transistors.
 
Thanks -- any idea how to go about checking a diode with 3 legs like these have? Also do they have to be taken out of circuit? (I don't have much experience with surface mount components.)

 
Same way as THT diode - one leg is not connected.
In the circuit you can check it in both ways - first with diode checker on multimeter, second measure the voltage.
 

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