MXL V63M how to open the case

[Rick H]

My V63M after 22 years has become noisy. I suspect bad caps. I live in Honduras and ordering a kit of parts is very expensive to ship here but I can buy parts locally. My first question is: How do I open the mic case to expose the circuit board?

 

[Khron]

My V63M after 22 years has become noisy. I suspect bad caps.

What sort of noise? And why caps?

And as in 99% of cases, you unscrew the bottom bell.

 

[rock soderstrom]

Welcome Rick,

My V63M after 22 years has become noisy. I suspect bad caps. I live in Honduras and ordering a kit of parts is very expensive to ship here but I can buy parts locally. My first question is: How do I open the mic case to expose the circuit board?

Yes, describe the noises (or record them) so that we can help you better. I suspect that your microphone has problems in the high impedance area or in the microphone capsule itself due to moisture (and dust?).

 

[Rick H]

First I must learn how to open the mic. I have instructions for that now. I suspect capacitors only by hunch. With 20 years old electronics caps are the first thing to look at. While I have the mic apart I will look for dust, clean up the circuit board, look at solder joints. I am well experienced with electronics repairs but this is the first microphone I have serviced.
The noise is a low level continuous noise, but random pops which make the microphone unusable. When I leave the mic powered for several hours the pops decrease in rate and volume (as if electrolytics are re-forming). The pops are the bigger issue.
I now have the mic disassembled.

 

[Rick H]

At first visual inspection, the insides are very clean, like brand new. No visible dust.

 

[rock soderstrom]

The noise is a low level continuous noise, but random pops which make the microphone unusable. When I leave the mic powered for several hours the pops decrease in rate and volume (as if electrolytics are re-forming). The pops are the bigger issue.

the symptoms you describe match my diagnosis very well, this is not an unknown problem that you describe. I suggest you replace the capsule with another (working capsule) or install a ca. 60pF capacitor as a “dummy capsule”. If the problem is then gone, you know what is going on. An intensive cleaning of the high impedance area with 99% alcohol would also not be wrong, the impurities / moisture are usually not visible to the eye.

Sometimes it also helps to place the microphone in a dry, warm place for a some days...

 

[rock soderstrom]

I am well experienced with electronics repairs but this is the first microphone I have serviced.

The situation in condenser mics is indeed somewhat special due to the extremely high impedances (1G!). Even the slightest contamination lead to the problems you mentioned.

 

[Rick H]

the symptoms you describe match my diagnosis very well, this is not an unknown problem that you describe. I suggest you replace the capsule with another (working capsule) or install a ca. 60pF capacitor as a “dummy capsule”. If the problem is then gone, you know what is going on. An intensive cleaning of the high impedance area with 99% alcohol would also not be wrong, the impurities / moisture are usually not visible to the eye.

Sometimes it also helps to place the microphone in a dry, warm place for a some days...

Thanks for the tip. I cleaned the cartridge and exposed side of the PCB in the area of the preamp. The pops have gone away, There is some low level noise left even with the cartridge replaces with a 68 pF cap. The mic is now in a warm place overnight. I will leave it there another day.

 

[MicMaven]

intensive cleaning of the high impedance area with 99% alcohol would also

I am impressed by the amount of crud remaining on low cost circuit boards.

Could I carefully use 70% alcolohol instead? I would apply it to a soft toothbrush or a one of my special static-free brushes on the workbench, opposed to soaking or spraying the board.

[Someday, I will buy a dedicated board cleaning solution ... but, shoot, that would cost real money and cut into my bourbon and chocolate budget.]

Thanks - James

 

[Migs 31]

I am impressed by the amount of crud remaining on low cost circuit boards.

Could I carefully use 70% alcolohol instead? I would apply it to a soft toothbrush or a one of my special static-free brushes on the workbench, opposed to soaking or spraying the board.

[Someday, I will buy a dedicated board cleaning solution ... but, shoot, that would cost real money and cut into my bourbon and chocolate budget.]

Thanks - James

I have had really bad experiences with those cheapo Chinese mics over the years: MXL & SP etc.
The residue left after soldering is obscene, at the same time if you have to produce a 100 units a day to get your pay cheque, you can't pay attention to detail and cleanliness.

I found 90 degrees disinfecting Alcohol at my local Pharmacy.
That alcohol and a tooth brush works really well.
Warning! : keep it away from Styrene caps and the membrane of your Mic Capsule.

M

 

[rock soderstrom]

Could I carefully use 70% alcolohol instead? I would apply it to a soft toothbrush or a one of my special static-free brushes on the workbench, opposed to soaking or spraying the board.

A long time ago, a recognized expert advised me to use only very high-percentage types of alcohol for such cleaning jobs, as they leave no residue when they evaporate. Every percent of water could be a problem. I don't know how important that is, but I've stuck to it and have done well so far.

Until recently, I always bought this at the local pharmacy, where I was always strictly questioned what I was going to do with it and the quantity was limited to 200ml. Really!

But now I've found this 1L bottle for around €9, which lasts forever at the local (Obi) hardware store.

Warning! : keep it away from Styrene caps and the membrane of your Mic Capsule.

This should be taken seriously, some plastics don't particularly like high-percantage alcohol either. Caution: very flammable, evaporates quite quickly at room temperature.

 

[Migs 31]

" at the local pharmacy, where I was always strictly questioned what I was going to do with it "

HAAAAAA!!!
"I'll drink it with my GDIY Alkie friends!!!"
Should have been your reply!
M

 

[rock soderstrom]

HAAAAAA!!!
"I'll drink it with my GDIY Alkie friends!!!"
Should have been your reply!
M

Cheers lads!, but I rather had the impression that the pharmacist suspected me of building something really dangerous with it.

I have no idea what you can do with it, I wasn't that active in chemistry lessons back then...