Kookie's Blue Kiwi repair thread

[micolas]

Yaaayyyy, I'm excited!!!

Oh well, that's how you learn I guess.

Well, you have to use 99° isopropyl alcohol not ethyl alcohol
But beware some components (eg styroflex capacitors) are destroyed at such a high concentration.

 

[pmfalcman]

Yaaayyyy, I'm excited!!!

Oh well, that's how you learn I guess.

Instead of tweezers you can use fire*.
A small hand-held torch or a lighter but of the wind resistant kind.
Sweep the PCB with flame, in tight passes. Not too slow! Do not worry, it will not damage anything, just will burn these tiny cotton threads. They're tiny, they burn up instantly. Just moderately swift pass will do.
Then clean with isopropyl alcohol and a (tooth) brush.


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*) if you have OCD - use tweezers

 

[SoundsOfJill]

Well, you have to use 99° isopropyl alcohol not ethyl alcohol
But beware some components (eg styroflex capacitors) are destroyed at such a high concentration.

Oh. ethyl alcohol won't dissolve the flux?

 

[micolas]

Instead of tweezers you can use fire*.
A small hand-held torch or a lighter but of the wind resistant kind.
Sweep the PCB with flame, in tight passes. Not too slow! Do not worry, it will not damage anything, just will burn these tiny cotton threads. They're tiny, they burn up instantly. Just moderately swift pass will do.
Then clean with isopropyl alcohol and a (tooth) brush.


----------
*) if you have OCD - use tweezers

An interesting approach,
pure diy style

 

[pmfalcman]

An interesting approach,
pure diy style

Pure pragmatism*.
Cotton burns faster than anything on the board. Flames up instantly. And anything withstands, say, 100 °C, right? Actually more than this but let's be very careful and conservative.
You will not heat up anything to more than 30°C with a swift pass of a flame. Even if 50°C - no harm can be done.
And the you just swipe off the charred remnants....



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*) Mixed with creative laziness

 

[pmfalcman]

Oh. ethyl alcohol won't dissolve the flux?

Isopropyl evaporates and leaves no traces.
That's why it's used to clean sensors and lenses in cameras.

In mics it's this highly sensitive Hi Z area that has to be free of any even remotely conducting matter of any kind.

 

[Khron]

Isopropyl evaporates and leaves no traces.

... Except maybe for some white residue in case there's any meaningful moisture around...

 

[pmfalcman]

... (...) white residue (...)

Have you bought colombian isopropyl by any chance?

 

[KrIVIUM2323]

Yaaayyyy, I'm excited!!!

Oh well, that's how you learn I guess.

Calm down, breathe and then proceed...
this is what i use for pcb cleaning:
https://www.directmedical.fr/protec...89fvONq6M6esH_ObJiqB_zbVoB78xXGxoCulgQAvD_BwE
https://www.amazon.fr/isopropyl-alcohol-99/s?k=isopropyl+alcohol+99
https://www.weldom.fr/p/brosse-a-joint-dexter-89124069

Glove are a must for any works in mic imho.
The brush is not exactly the same but you get the idea.
Tweezer are not a bad idea imho: once fully cleaned and dryed, before doing anything with resoldering you could try to plug the mic without body and try to see if sound come back when moving the parts with the tweezer.
Might help to identify the culprit.

Anyway given 'le travail de cochon' about soldering i would reflow every soldering points. Another thing i don't like is the tubing around the 1g resistors as you can't really see what was done in there.
I really dislike soldering works on the 4 pin connector to the capsule either... but if there is no issue from there then maybe leave it like that. I would be embarrased about it, to redo or not?

The very positive thing is you got it to work briefly so there is high hopes to bring it back to life definitely.
Intermitent faillure are a real pita but i'm sure you'll solve it, you seems resilient enough. Go Jill, go!

 

[micolas]

... Except maybe for some white residue ...

Have you bought colombian isopropyl by any chance?

The Colombian isopropyl is inhaled through the nose, it is not good for cleaning PCBs.

 

[Voyager10]

Looking at the circuit board pics, at least the audio bits, there's a schematic here which appears to be similar:
https://groupdiy.com/threads/help-f...fake-microphone-schematics.89000/post-1174255
(same number of FETs/transistors and diodes, some matching resistor values e.g. 620K, 30K)

If so, there's no great need to worry about FET biasing, as the operating current is set by the rest of the circuit (assuming the devices used are roughly the right type for the application).