Trying to repair an Oktava MK-119.

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wstratton

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Hi all,

A couple years ago I bought a few microphones made by the "revamped" Oktava--two MK-012s and an MK-119. All stopped working properly within a few months of buying them :/

I've given up on repairing the MK-012s on my own for the time being--I'll probably send them to Bill Sitler eventually and see if he can replace the whole PCB. But I've had the MK-119 sitting around for a while now, and given that the PCB's spacing is a little more generous, I thought I'd post a few pictures here and see if anyone has any suggestions for things to try.

This microphone still passes a signal if you crank the gain--sometimes--but it is very noisy with hum and hiss, and sounds like a very broad high pass filter has been applied. Anyone have recommendations for where to start?IMG_1036.jpg
IMG_1037.jpg
 

Whoops

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Both those mics, the MK-012 and MK-119 if the capsule is good and not shot the circuit itself is really easy to repair. and service.

Do you have the schematic for the MK-119?
 

Crosscut

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Looks like it needs the diaphragm cleaning.
There is a shadow on the right of the diaphragm as well that could be a tension problem.... or it could just be a reflection.
 

wstratton

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Thanks for the replies, everyone. It was marketed as being the same as the MK-319, but in a smaller body. Not sure if the circuit is truly identical aside from the lack of filters and pad. I'll try cleaning the capsule (gently). That shadow is just a reflection, the capsule is properly tensioned.
 

Whoops

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Thanks for the replies, everyone. It was marketed as being the same as the MK-319, but in a smaller body. Not sure if the circuit is truly identical aside from the lack of filters and pad.

Do you have a schematic dor the MK-119?
if not try to get one

I'll try cleaning the capsule (gently). That shadow is just a reflection, the capsule is properly tensioned.

Cleaning capsules is dangerous, it can do plenty of harm if it's not well made.
I don't see dirtiness in your capsule, even if it was dirty that hasn't anything to do with the problems you describe.
I would leave the capsule alone and not try to clean it

The problem might still be an electrical problem in the capsule.
Do you have any other capsule that you can connect to that circuit to test it out?
 

wstratton

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Do you have a schematic dor the MK-119?
if not try to get one



Cleaning capsules is dangerous, it can do plenty of harm if it's not well made.
I don't see dirtiness in your capsule, even if it was dirty that hasn't anything to do with the problems you describe.
I would leave the capsule alone and not try to clean it

The problem might still be an electrical problem in the capsule.
Do you have any other capsule that you can connect to that circuit to test it out?
Ah, good point. I'll leave the capsule alone. I don't have a schematic, but I'll look for one. I don't have a capsule on hand, but I'll get one to try out.
 

Whoops

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For the MK-012 you can even replace it with an improved pcb from Russell technologies,
pretty well made and easy to do the circuit and replace it:


They also have a PCB and circuit for the MK-219 (and the MK-319 which is the same circuit),
the pcb uses an improved circuit but uses the original transformer which you already have,
maybe you can use it in the MK119, you just have to compare schematic:

 

wstratton

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Interesting, thanks! In the case of the MK-012, my microphones have a narrower body than the vast majority of these microphones, which makes me suspect that this PCB will not fit.
 

Gus

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Search this forum for Oktava threads
There are schematics and post that you can use to check voltages. The circuits are simple.
Also search for other microphone issues there are threads that have things to test when you have issues with microphones

Are the microphones in a high humidity area, do you use them with a screen if used for voice etc.?

Have you tested the preamp with a known good microphone?

I don't think you need to build a new PCB like in Whoops post to me that would be a waste of time and money. The PCB in the pictures looks good to me


A hint if it is a noise issue look for posts about installing a cap in place of the capsule for a test
 

Crosscut

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Ah, good point. I'll leave the capsule alone. I don't have a schematic, but I'll look for one. I don't have a capsule on hand, but I'll get one to try out.
The symptoms you describe are the symptoms of a dirty capsule
We can see from the photo (a bit blurred but clear enough) that the capsule needs cleaning.
I wouldn't bother trying anything else until you have done that and it hasn't worked, been there, I spent a long time switching out components/re-capping/re-soldering a mic once, (I even replaced and rebiased the FET which was a whole level more time consuming and complicated than just cleaning the capsule), but to no avail, until I finally got the courage to clean the capsule, problem solved. I then went through all my LDC mics and any problems they had were solved by cleaning too.

So you are faced with two choices

1. find someone to clean the capsule
2. learn to clean the capsule

if you choose to learn yourself there are a couple of things I found helpful.

  • Use distilled water- no need to mix other things in with it, some suggest isopropyl alcohol but I don't think it really helps and can contain impurities
  • A fine sable brush
  • the technique I try and use is to actually avoid touching the diaphragm with the brush - use the brush to carry the drop of water to the surface, then coax the water across the surface by brushing the water (not the diaphragm) I hope that makes sense, it helps to hold the capsule at an angle, let gravity help you, a good light and magnifier really helps. You can actually see the impurities getting lifted into the water from the surface of the capsule.
  • Once the water is "coaxed" to the edge of the diaphragm soak it up with a soft tissue, no rubbing, just dip a dry corner into the droplet and wick the moisture up.
Go steady, practice on the cheapest mic you have. This will solve 90% of problems with LDC mics.
 

mrgrooves666

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That looks like standard MK319/219, only difference being that the capsule is without the usual disk resonators and the mic without the HP and pad I guess. Interesting, it seems like the upgraded Joly/oktavamod version directly from oktava?.
 

mrgrooves666

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If its the same symptoms with your 012, it might be that you're keeping them all in humid conditions. The 012 capsules for ex, are very prone to caught humidity. Even before cleaning the 119 capsule, I would leave the mic in a dry place, exposed at the SOFT heat of a light bulb for a couple of hours, or stick the mic in a bag with silica gels bags for a couple of hours. As for the 012 capsule, its easy to dissasemble to dry, I've done this with all the 012 SD capsules and the MK-103 as well, follow this video:
 
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wstratton

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Hey all, thanks very much for all the advice. Regarding the MK-012s: I already tried all the tricks for dehumidifying the capsules. They won’t pass a signal anymore. The MK-119 barely passes a signal, so I don’t think it’s a matter of a dirty capsule. I did end up learning how to clean the capsule and I did so—thanks for the recommendation. It didn’t change the signal much—maybe a tiny bit. I think my next steps are going to be to try to source a replacement capsule for one of the MK-012s to see if the capsules are defective. Then I will probably find a decent replacement capsule for the MK-119 and see if that does the trick. After thinking about it all, I agree that the most obvious culprits would be the capsules.
 

Gus

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Did you look up how to sub in a cap for the capsule to test if the capsule is the source of the noise?

Do the simple nondestructive things first

Have you tried other microphones with the preamp or audio interface?

Have you checked the preamp phantom supply? Shure has a nice write up on how to do this.

Have you checked the cable?

What preamp/interface are you plugging the microphones into?

The capsule should be down further on the list of things to work on.
 
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wstratton

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Location
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Did you look up how to sub in a cap for the capsule to test if the capsule is the source of the noise?

Do the simple nondestructive things first

Have you tried other microphones with the preamp or audio interface?

Have you checked the preamp phantom supply? Shure has a nice write up on how to do this.

Have you checked the cable?

What preamp/interface are you plugging the microphones into?

The capsule should be down further on the list of things to work on.
By cap, do you mean capacitor or capsule in that sentence? I’ll read up on that. Aside from that, I’ve done all the rest—all the simple options have been exhausted. Thanks though!
 
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