Troubleshooting and repairing microphone circuit board and jack

[rob3rto]

I've had my Monarch (Excelsior) pro Musette for about a year. Over the past few weeks the keyboard side microphone output has developed a hefty buzz, and sometimes will not produce instrument sound at all. For the moment I prefer using the internal mic system as it mitigates feedback issues with my four piece band (me, acoustic guitar, upright bass, and violin) and the full tone of the instrument is not really important at the venues we're playing. My mic system is a single stereo jack output with a pot for bass and treble each. The board and mics are mounted in the grill.

I haven't done much work inside an accordion to this point, and while I'm ok with give a it a try-especially on the microphones-I'm not sure how to go about diagnosing this issue. I think normally a short would be pretty on the keyboard side-just look at the wires to and from the harnesses and focus on the one the that looks the worst. I do have a candidate where the casing is separating from the wire, but I also noticed that some capacitors (I think) may be damaged. I couldn't find a way to capture it very well in the photos, but it appears that they are butting up against the switch brackets when the grill is closed. If that's indeed the case, the only solution I can think if is looking for or creating a new circuit board that has components that don't stick out so much. I don't think there is enough room on the grill cover to drill new holes for the pots to move the board downward where the components wouldn't collide with the switch brackets.

For those of you with experience, how would you approach this issue? Many thanks in advance.
-Robert

 

[debra]

My approach: with the grille removed...
1) Check battery voltage.
2) make sure the circuit board isn't touching the grille anywhere (see if you can push a sheet of paper between board and grille).
3) clean contacts of the jack plug because it normally not only transmits signal but also functions as an on/off switch.
4 with the mic connected to an amp, wiggle each wire to find potential lose connections.
If nothing helps... switch your brain over from accordion player to electrical engineer and start testing the components or the system... (and no, I'm not an electrical engineer, but I know a bit about electronics)

 

[jozz]

see Paul point 2:

how is that board shielded from the aluminium grille?

looks like its very easy for a pin to touch

 

[rob3rto]

Thanks very much for your replies. To answer the question about the board being shielded, I double checked and there is pad between it and the grill.

I believe the ground is shorted inside the jack after using Paul's method step 4. I found that the buzzing stops when the exposed portion of the feed wires from the board to the jack touch the metal sheeting inside the grill, and the microphones are still active. The solder points on the jack are solid, and manipulating them or the wires don't alter the buzz.

I have enacted the jankiest fix I can think of as a temporary stopgap (see pictures). I've used electrical tape to keep the wires flush with the grill cover. I'll carry the tape with me as well as an SM57 to my upcoming gigs in case my emergency surgery fails to hold.

Are folks in agreement with my diagnosis? If so, does anyone have direction on where to find a compatible jack? I've run a cursory search, but the options and variations are immense.

 

[debra]

What I suggest is to make sure you have a good ground connection between the ground of the mic system and the grille. It looks like the threaded part of the jack connector you have is insulated (plastic). You could string a wire from the ground around that and then by means of the nut that secures the connector in place you have a ground connection. I'm surprised the mic system never had a ground connection to the grille.

 

[rob3rto]

Ok that's a good idea. Now that I think about it I wonder why the bass side isn't buzzing as well, but I'll try rigging a ground to the grill and see what happens.

Thanks much for your input!

 

[debra]

Ok that's a good idea. Now that I think about it I wonder why the bass side isn't buzzing as well, but I'll try rigging a ground to the grill and see what happens.

Thanks much for your input!

It's common (electronics) sense: when you have any type of audio equipment it typically has a metal housing (shielding against electrical disturbance) and that is always grounded. But... the jack connector is of an insulated type because if there were more than one and more than one was grounded then you get a ground loop and that causes a hum. So by using an insulated connector you get the choice where to ground the circuit (and ground it just once).

 

[jozz]

you arent accidentally using a TS rather than a TRS jack?

TS could short that socket in that manner?

 

[debra]

you arent accidentally using a TS rather than a TRS jack?

TS could short that socket in that manner?

Good point! If you use a stereo cable to connect to what actually is a mono amp then the "shorting" that is needed to turn on the mics happens at the far end of the cable and that's not good enough. The cable used must be a mono cable (mono jacks on both ends).

 

[Ventura]

if you remain concerned about the two Capacitors, a future improvement
is as simple as buying 2 new 100mf 16V or better (but same physically sized around)
as they will come with long legs/leads

(by better i mean, you cannot use a value LOWER than original, but you
can exceed it... in that part of the circuit, the caps act as small reservoirs of power only
and a slightly larger value is like extra insurance)

instead of trimming them short and mounting upright as original, slip about 1/2" of
any spare tubing onto the legs to insulate them, then bend the remaining exposed metal
of the legs at right angles THEN pass them through the circuit board and solder in place

to make up for their flexibility, add a dab of Silicone Caulk to hold them firmly... there is
plenty of room on the board to affix them in this manner

i keep a small tube of clear on my workbench (the kind you get at the Auto Parts store)

where you put electrical tape on the wires ? i would use Silicone there also, then after
it cures remove the tape

tape can be messy and can fall off... silicone caulk is a great insulator as well... many techs
fill the insides of audio jacks after we solder them just before we screw the barrel back on
as it helps the wires resist being pulled out

i would also make a better, more permanent link to grounding the grille

one other approach would be to mount a tiny toggle switch to turn power off and on, then you
could switch to a simple, more robust and rugged Switchcraft 3 way which will ground the grille
very firmly

i personally never liked the hidden switching nor those plastic jacks that really should
only be used mounted directly to circuit boards (my opinion)

 

[debra]

...

i would also make a better, more permanent link to grounding the grille

one other approach would be to mount a tiny toggle switch to turn power off and on, then you
could switch to a simple, more robust and rugged Switchcraft 3 way which will ground the grille
very firmly

i personally never liked the hidden switching nor those plastic jacks that really should
only be used mounted directly to circuit boards (my opinion)

I like the volume knobs that have a built-in on-off switch. Such potentiometers are easy to come by and solve the problem that the plug has to short the ground to turn on the unit. The Microvox power box has a volume knob that switches the unit off when volume is turned all the way to zero. It also shuts off when you unplug the cable but I disabled that functionality because it involves shorting ground with the jack and that is prone to failure mid-performance...

I do not object to the plastic jack units. In fact, they are a necessity when you have multiple inputs and/or outputs as when they are all metal and all grounding the housing you get a ground loop causing a hum. I have seen even a case of two speakers that each have their own power plug and when both were connected to a grounded outlet and then both to the same pre-amp/mixer there would be a hum. One of the speakers had to go into an ungrounded power socket (or use an ungrounded short extension cord) to avoid the hum. I built my own pre-amps and power-amps in the past and had to make sure that all audio in- and outputs were insulated from the unit's housing (which was connected to ground in the power supply). Otherwise ground loops would cause a hum. The pre-amp and power-amp could also not both go to a grounded power-outlet or there would be a hum. It's all so tricky...

 

[rob3rto]

you arent accidentally using a TS rather than a TRS jack?

TS could short that socket in that manner?

I'm the 2nd owner, but I'm nearly positive this is the factory installed jack. It is TRS as it used to work properly before it shorted.

 

[rob3rto]

if you remain concerned about the two Capacitors, a future improvement
is as simple as buying 2 new 100mf 16V or better (but same physically sized around)
as they will come with long legs/leads

(by better i mean, you cannot use a value LOWER than original, but you
can exceed it... in that part of the circuit, the caps act as small reservoirs of power only
and a slightly larger value is like extra insurance)

instead of trimming them short and mounting upright as original, slip about 1/2" of
any spare tubing onto the legs to insulate them, then bend the remaining exposed metal
of the legs at right angles THEN pass them through the circuit board and solder in place

to make up for their flexibility, add a dab of Silicone Caulk to hold them firmly... there is
plenty of room on the board to affix them in this manner

i keep a small tube of clear on my workbench (the kind you get at the Auto Parts store)

where you put electrical tape on the wires ? i would use Silicone there also, then after
it cures remove the tape

tape can be messy and can fall off... silicone caulk is a great insulator as well... many techs
fill the insides of audio jacks after we solder them just before we screw the barrel back on
as it helps the wires resist being pulled out

i would also make a better, more permanent link to grounding the grille

one other approach would be to mount a tiny toggle switch to turn power off and on, then you
could switch to a simple, more robust and rugged Switchcraft 3 way which will ground the grille
very firmly

i personally never liked the hidden switching nor those plastic jacks that really should
only be used mounted directly to circuit boards (my opinion)

Thanks for the excellent suggestions Ventura. Yes, the tape is only a stopgap for the gig I played over the weekend and has already been removed. Following @debra 's advice, I'm working on a direct ground to the grill. The wire I have on hand is too thick of a gauge to make good a solder point on the jack, but I was able to proof of concept that the buzz is eliminated. I'll have to finish up midweek.

I did notice that the switch bracket is shaved to make room where the capacitors hang. I've placed a small bit of electrical tape there as a buffer for now, and appreciate your advice on addressing them. I will have to put the part of the project off for a while (assuming they remain functional).

 

[JIM D.]

I've been extremly busy for the past weeks on renovations to my home & shop but have reading this tread for a while and thouht
you would have it solved by now. I don't have your accordion in the shop but from this tread and your pic's you do have a missing
or leaking ground. I going to make a knowledgeable guess here -- your ground problem is caused by that 10 cent plastic stereo
output jack. This is a common problem with musical instruments that use these. In your instance I would replace the plastic jack with

Amazon.com: Switchcraft 12B Stereo TRS Female 1/4-Inch Jack with Washer and Nut, Nickel Finish: Musical Instruments

Buy Switchcraft 12B Stereo TRS Female 1/4-Inch Jack with Washer and Nut, Nickel Finish: Electronics - Amazon.com ✓ FREE DELIVERY possible on eligible purchases

www.amazon.com

This jack will also ground the grill.

 

[rob3rto]

I don't have your accordion in the shop but from this tread and your pic's you do have a missing
or leaking ground. I going to make a knowledgeable guess here -- your ground problem is caused by that 10 cent plastic stereo
output jack. This is a common problem with musical instruments that use these. In your instance I would replace the plastic jack with

Amazon.com: Switchcraft 12B Stereo TRS Female 1/4-Inch Jack with Washer and Nut, Nickel Finish: Musical Instruments

Buy Switchcraft 12B Stereo TRS Female 1/4-Inch Jack with Washer and Nut, Nickel Finish: Electronics - Amazon.com ✓ FREE DELIVERY possible on eligible purchases

www.amazon.com

This jack will also ground the grill.

This is great, thank you for the suggestion, I will order one straightaway.

 

[jozz]

I'm the 2nd owner, but I'm nearly positive this is the factory installed jack. It is TRS as it used to work properly before it shorted.

yes but i mean the cable

are you inserting a stereo cable/jack?

accedentally using a standard mono cable would short out your socket

 

[debra]

I've been extremly busy for the past weeks on renovations to my home & shop but have reading this tread for a while and thouht
you would have it solved by now. I don't have your accordion in the shop but from this tread and your pic's you do have a missing
or leaking ground. I going to make a knowledgeable guess here -- your ground problem is caused by that 10 cent plastic stereo
output jack. This is a common problem with musical instruments that use these. In your instance I would replace the plastic jack with

Amazon.com: Switchcraft 12B Stereo TRS Female 1/4-Inch Jack with Washer and Nut, Nickel Finish: Musical Instruments

Buy Switchcraft 12B Stereo TRS Female 1/4-Inch Jack with Washer and Nut, Nickel Finish: Electronics - Amazon.com ✓ FREE DELIVERY possible on eligible purchases

www.amazon.com

This jack will also ground the grill.

I have used these a number of times over the years. They work well for cases like this where you want just one ground connection. (Cannot use these metal ones on something like an audio mixing table as you would get ground loops.
I have Microvox mics and they use a plastic connector (grounding the casing elsewhere) and I have the cheap mics from Carini and these too come with a plastic connector and the ground is made on one of the two volume potentiometers. Like jozz I am more and more suspicious that a stereo cable was used by mistake, instead of a mono one and that this is causing the problem.

 

[rob3rto]

are you inserting a stereo cable/jack?

accedentally using a standard mono cable would short out your socket

When I first got the accordion I tried a mono cable and only heard the bass side (minus residual bleed through).

 

[Ventura]

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 !

 

[debra]

When I first got the accordion I tried a mono cable and only heard the bass side (minus residual bleed through).

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...)