Noob needs help with z5600a II mic repair

[Adam Frandsen]

Be warned - be careful. If you spray ANYWHERE near the capsule you will get micro-droplets of acrylic coating the diaphragm(s) - this will make the diaphragm heavier and completely change the frequency response and if uneven will unbalance the surface, affecting wave propagation that occurs on the diaphragm. Unless you mask the diaphragm with a soft cloth and then clingwrap or remove the circuit board to spray it you will ruin the capsule.

This I will of course make sure to do, thanks for the warning. But do you otherwise think it is a good idea to do?

 

[RoadrunnerOZ]

Once all the components are soldered on and it looks like you are doing this with the circuit board in place, you will need to remove the cage/basket to expose the capsule so you can mask it properly - spray will drive through the gap at the top of the circuit board. For myself I would remove the board to fit the components and then spray. Keep the rest of the assembly out of the room you are spraying in as overspray carries a long way.
I do tech work and quality control analysis (as well as studio audio and keyboard repairs) for a specialist car company doing body repairs on luxury Supercars (Lamborghini, Ferrari, Rolls Royce, Maserati etc) and in the spray booths everything is masked that’s not being painted, using sheet plastic film and special masking tape to completely seal the vehicle and using negative air pressure extraction systems. Anything sprayed under pressure generates a cloud of particles that can travel up to 30 feet and settle and stick to any surface and also carries solvent thinners that can cause damage.
A tiny gap in the masking will shoot a jet of spray particles all over the surface that’s exposed and you can’t get it off! Also some spray solvents, which are part of the spray lacquer, can soften the plastic of the diaphragm causing it to lose tension - this reduces the high frequency response radically, so any spray work done in close proximity to the diaphragm is risky.

 

[RoadrunnerOZ]

This I will of course make sure to do, thanks for the warning. But do you otherwise think it is a good idea to do?

Doing this will prevent moisture that can cause capacitance and resistance changes to parts of the circuit due to exposed print and solder points. There is a protective mask over the print so the conductivity due to moisture is only between soldered points. However this is only temporary as moisture condenses from the atmosphere when your mic cools down after use but will dry out with the heat of the tube on warmup again, but dust settling on the board can stick to the moisture and eventually cause problems but it’s pretty low risk.

 

[Adam Frandsen]

Once all the components are soldered on and it looks like you are doing this with the circuit board in place, you will need to remove the cage/basket to expose the capsule so you can maski it properly - spray will drive through the gap at the top of the circuit board. For myself I would remove the board to fit the components and then spray. Keep the rest of the assembly out of the room you are spraying in as overspray carries a long way.
I do tech work and quality control analysis (as well as studio audio and keyboard repairs) for a specialist car company doing body repairs on luxury Supercars (Lamborghini, Ferrari, Rolls Royce, Maserati etc) and in the spray booths everything is masked that’s not being painted, using sheet plastic film and special masking tape to completely seal the vehicle and using negative air pressure extraction systems. Anything sprayed under pressure generates a cloud of particles that can travel up to 30 feet and settle and stick to any surface and also carries solvent thinners that can cause damage.
A tiny gap in the masking will shoot a jet of spray particles all over the surface that’s exposed and you can’t get it off! Also some spray solvents, which are part of the spray lacquer, can soften the plastic of the diaphragm causing it to lose tension - this reduces the high frequency response radically, so any spray work done in close proximity to the diaphragm is risky.

I will spray it into a plastic bag then on my balcony and use a soft brush to apply it instead then. But is it worth it, or does it not make much difference?

 

[RoadrunnerOZ]

It won’t make a great deal of difference - the AKG mics have it done in the factory but once you desolder any components and solder in new ones you break that seal. Using the lacquer with a fine artists brush is the best idea - too much hassle with spraying. When I do Juno 106 voice cards I remove all the very thick epoxy covering and pick it out from between the legs of the surface mount IC’s as this stuff becomes hygroscopic after a few years and causes weird drifting of the filters - once done I then spray the whole card with protective lacquer which I do outdoors.
When I do microphone repairs or restoration I only use a brush on the affected solder joints of any replaced parts and the legs of the components on the other side of the board to bring it back to factory standards.

 

[Khron]

I don't think i've seen conformal coating used in any mics using through-hole components. Especially if the high-impedance nodes are lifted off the board (either in the air, or on Teflon isolation pins), there's arguably no point really.

I've seen dabs of conformal coating, or some sort of lacquer, used in some Rode mics that use all surface mount components, and even there, only in the jfet input area.

I definitely wouldn't use a spray though, too heavy-handed and inaccurate. For through-hole stuff i wouldn't bother; for surface mount i'd rather use a conformal coating pen (like CW3300 - pick your favorite color).

 

[RoadrunnerOZ]

I don't think i've seen conformal coating used in any mics using through-hole components. Especially if the high-impedance nodes are lifted off the board (either in the air, or on Teflon isolation pins), there's arguably no point really.

I've seen dabs of conformal coating, or some sort of lacquer, used in some Rode mics that use all surface mount components, and even there, only in the jfet input area.

I definitely wouldn't use a spray though, too heavy-handed and inaccurate. For through-hole stuff i wouldn't bother; for surface mount i'd rather use a conformal coating pen (like CW3300 - pick your favorite color).

AKG C12 VR with original factory coating easily visible as it’s gold in colour - everything sprayed with all components fitted, prior to fitting to chassis and switches - you can also see it on the resistors and capacitors (not sure if sprayed or dipped as it’s quite a thick coating both sides of the boards).

 

[Khron]

Ok, that's one. Not sure it's famous for being particularly low-noise, but what do i know?

 

[RoadrunnerOZ]

Ok, that's one. Not sure it's famous for being particularly low-noise, but what do i know?

Not sure if I see the point really unless the boards are made without solder mask.

 

[Adam Frandsen]

I have two questions, sorry if the answer is obvious:

3 points where the solder pads are so close (basically touching) that it is almost impossible for me to solder them separately without the solder of the two pads joining together. Is this on purpose, should they connect, it almost seems like it:

1. r8,c9
2. c4,r4
3. r5,r7

Another question: the leads for the capsule have no longer any (too little) of the lead exposed, how do I best strip those tiny wires…

Everything else seems good, all is soldered on except the leads…

Thanks again,
Adam

 

[Khron]

R8 does indeed connect to C9 (and also one end of the 1gohm R1), otherwise there's nothing to provide the 60v to the capsule backplate.

C4 is, as per the schematic, connected in parallel with R4 and C5 (one end in common, and going to the first triode's cathode, and the other end of each/all going to ground).

R5 does indeed connect to R7, and one end of C8; otherwise there's nothing feeding the B+ high voltage to the first triode's anode; otherwise, no signal.

Regarding wire stripping, unless i need to be doing bulk quantities, i just roll the wire, LIGHTLY (especially if it's thin), between my thumb and a fresh / sharp section of my box-cutter's blade, so i just slice through enough (or even all) of the insulation, but no (or very few) strands of copper, and then just pull off the (mostly) separated piece of insulation.

 

[Adam Frandsen]

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R8 does indeed connect to C9 (and also one end of the 1gohm R1), otherwise there's nothing to provide the 60v to the capsule backplate.

C4 is, as per the schematic, connected in parallel with R4 and C5 (one end in common, and going to the first triode's cathode, and the other end of each/all going to ground).

R5 does indeed connect to R7, and one end of C8; otherwise there's nothing feeding the B+ high voltage to the first triode's anode; otherwise, no signal.

Regarding wire stripping, unless i need to be doing bulk quantities, i just roll the wire, LIGHTLY (especially if it's thin), between my thumb and a fresh / sharp section of my box-cutter's blade, so i just slice through enough (or even all) of the insulation, but no (or very few) strands of copper, and then just pull off the (mostly) separated piece of insulation.

Awesome - one more thing, I soldered the red leads from the diaphragm to D1 and D2 as they were, the black wire was connected to the 1Gohm/1000pf joint/pin, so I soldered it to the leg of the 1gohm resistor that runs into that joint, because it was easiest and allowed for more space when soldering, this should be ok, right? one thing I did not mark, was which point I need to solder the tube socket red wire to on the back of the PCB, really stupid oversight, and again sorry if the answer is obvious,

 

[RoadrunnerOZ]

Do you have photos of the back of the board before disconnecting? What pin number is the red wire on the socket base?

 

[Adam Frandsen]

Do you have photos of the back of the board before disconnecting? What pin number is the red wire on the socket base?

Thats the whole problem, I don’t have a picture where it is visible, because it is somewhere behind the socket itself

 

[Adam Frandsen]

Do you have photos of the back of the board before disconnecting? What pin number is the red wire on the socket base?

This is how it looks now, btw. it isn't attached, just looks like it

 

[RoadrunnerOZ]

This is how it looks now, btw. it isn't attached, just looks like it

I assume you mean it’s not attached to the board as it sure looks like it’s soldered to pin 2 of the tube socket. This is G2 of the tube which in the schematic shows being connected to the side of C1 that is not attached to the backplate of the diaphragm, this is the junction of C1 R2

 

[RoadrunnerOZ]

Thats the whole problem, I don’t have a picture where it is visible, because it is somewhere behind the socket itself

Did the wire break off or did you disconnect it?

 

[RoadrunnerOZ]

I would assume this was originally connected to where the leg of C1/R2 comes through the board on the back (tube) side or to an edge connection that runs from that junction point on the front side - it’s pretty easy to trace the print with your eyes - if you can’t see it on the other side of the board is the wire long enough to run to the front of the board?

 

[Adam Frandsen]

Did the wire break off or did you disconnect it?

It broke off, I can just attach it to the pin that connects r2 and c1 on the underside of the pcb where the tube is, it goes through the board. Thanks a lot!

 

[RoadrunnerOZ]

Also make sure of the polarity of the front and rear diaphragm wires - are they the same colour?