Troubleshooting and repairing microphone circuit board and jack

[debra]

Debra, for the insulated jacks, Switchcraft also has a very robust version
which were used on the original Chordovox... they come in a number of 2, 3, and
4 point variations plus the switching function on a separate lead

it is the style of those flat ones and the tiny weak springs they use that i dislike

oh, and BTW those ungrounded Power amps are handy when you want to surprise the
Guitar player or the Vocalist !

Many of these plastic jack boxes are made of plastic that is really too weak, so if you tighten the nut just a bit too much you destroy the threads. That's another problem besides the weak springs... If the springs on the open metal one become too weak you can bend them a bit and improve the situation.
I do not recommend to use ungrounded power amps. It's important that everything is grounded, but there should be no ground loops. That can be a bit of a puzzle...

 

[jozz]

This suggests that the mics are really stereo... but then, what turns the mics on and off? (They should not be on all the time as that drains the battery...)

TRS sleeve = ground

mono sleeve shorts R signal to ground, thus passing only tip/L

 

[JIM D.]

In some of these system types, removing the plug wil shut off power to mics

 

[debra]

In some of these system types, removing the plug wil shot off power to mics

In all cases I've seen this it's a mono system, using a stereo socket and getting the mono plug's long ground part to short between what's the right channel in stereo to ground. How does a system with stereo mics and 1/4" jack turn on/off power when the plug is inserted/removed? It cannot use the common method of shorting ground by means of what is the right channel in stereo... Do they have a switch mechanism added to the ground "spring" or something like that?

 

[jozz]

The sleeve of the stereo plug will make the circuit and works the same way as mono sleeves.

 

[debra]

The sleeve of the stereo plug will make the circuit and works the same way as mono sleeves.

Thanks. So the "short circuit" is then just further down the sleeve. Makes sense.

 

[rob3rto]

Hey all, I've received the new jack and some other supplies. The TRS jack of course has three mount points, but the wire harness I'm dealing with has four wires. As a novice in this area I cannot figure out what I'm looking at and whether I can use the existing wiring reconfigured to work with the new jack. I've attached several pictures of the harness wiring, as well as the wiring that comes in from the bass side (taped to the switch bracket to keep in place during the interim). On that you can see how they've split the blue wire into whatever it is, and a ground.

Is the new jack useable without substantial rewirings? Between the day job, practicing, playing weekend gigs, and attempting to be a present member of my family I may just have to jimmy a ground to the grill for the time being and come back to the new jack over the holidays or when there's a lull.

 

[jozz]

to be sure we need to see pics of the actual mic capsules and how they are wired. i guess you have battery at the bass side? that would explain 4 wires coming from there

i guess you have ground arrow right, that single pin in the center should touch the sleeve

 

[jozz]

in the meantime, simply try to reflow the connections on the black block.

it is highly unlikely it actually needs a chassis/grille ground,

and much more likely one of the connections having to do with treble ground is bad

 

[rob3rto]

Thanks

it is highly unlikely it actually needs a chassis/grille ground,

and much more likely one of the connections having to do with treble ground is bad

Ok thanks. I think I agree, but the method of creating a manual ground from the black wire/solder point on the jack, to the grill, eliminates the buzz. So that may end up being my short-term workaround. I'll post pictures of the bass side soon.

 

[debra]

Let me throw a curve-ball here...
This mic system has worked well, without the grille being grounded, right?
Now it suddenly developed a hum, which disappears if you ground the grille, right?
What this may indicate is that the "live" wire of one of the mic capsules may be touching the grille, which then acts as a huge hum-pickup. If this is the case, one of the mic capsules should be non-functional when you ground the grille. So what you can test is whether, with the grille grounded, all capsules are still working. Just tap each one lightly while the accordion is hooked up to an amp, and see (listen) whether each mic is picking up the tap. We know you did check that there was no short between the main circuit board and the grille, but don't know about each separate mic. Would you please perform this test? So far we have not really tackled the situation that the mic system was working without hum in the past (while also not being grounded)...

 

[rob3rto]

Let me throw a curve-ball here...
This mic system has worked well, without the grille being grounded, right?

If memory serves. I didn't plug it in but once or twice over lockdown, but let's go with "yes".

Now it suddenly developed a hum, which disappears if you ground the grille, right?

Yes.

What this may indicate is that the "live" wire of one of the mic capsules may be touching the grille, which then acts as a huge hum-pickup. If this is the case, one of the mic capsules should be non-functional when you ground the grille. So what you can test is whether, with the grille grounded, all capsules are still working. Just tap each one lightly while the accordion is hooked up to an amp, and see (listen) whether each mic is picking up the tap. We know you did check that there was no short between the main circuit board and the grille, but don't know about each separate mic. Would you please perform this test? So far we have not really tackled the situation that the mic system was working without hum in the past (while also not being grounded)...

All three treble mics have the same response to tapping when the manual ground is in place..

For now, I'm going to add a solder point to the ground post on the jack, and wrap the other end around the jack input so it's flush with the grille (as you previously mentioned). This will allow me to play my preferred accordion at tonight's gig with the internal mics. I've proofed this without the solder, so it should be a pretty good fix for now.

My preference in the future would be to use the new TRS jack wired properly, but as I've mentioned that might have to wait for a while.

I greatly appreciate the assistance I've been receiving from this thread.

 

[debra]

...

I greatly appreciate the assistance I've been receiving from this thread.

Sadly "remote diagnosis" is notoriously difficult. We're really swimming in the dark here...

 

[rob3rto]

Sadly "remote diagnosis" is notoriously difficult. We're really swimming in the dark here...

True, true, but I have been able to to enact a fix that should work for the near future.

While I was working on the solder the ground wire came out of the crimp box (not sure that's what it's called, the cradle that feeds from the circuit board to the jack on the treble side). That was the connection that looked suspicious from the get-go, and I'm thinking it was not set well when it was first connected. That almost broke the deal but I was able to carefully get some solder into the pin connecter and reset the wire. I don't think this is related to what we're troubleshooting here, but it probably does put the full fix out of my reach. I'll work on finding someone local I can work with to schedule a repair or tutoring session. That whole crimp box will have to be replaced and rewired to connect to the new jack if I'm not mistaken.

FWIW, I'm thinking that whatever grounding setup was present in the jack (a literal "black box") must have shorted. Also FWIW, I think my accordion should have the same specs a comparable Excelsior (LMMM, no cassotto, perhaps a 911?) of the past 5 years, but I don't know what standard the mic systems are.

 

[JIM D.]

Happy to hear you at least have a working accordion. It was obvious that the plasic jack was failing. Using the accordion in its
present wiring will not harm it until you find an accordion or electronic tech to wire the mikes pots & power in correct sequence.