Early warning symptoms of bad piezo?

[soundog]

I have a Variax Acoustic 700 I've used for many years. Lately at a gig the low E string has no output until the unit has "warmed up". After that it works normally.

 

Is this a symptom of an aging piezo like one of these, or do piezos just suddenly stop working.

 

 

[Charlie_Watt]

Often it is just a problem of a bad ground connection.  If you remove the strings and clean the piezo it my start working reliably again.  It relies on the case for it's ground and it can get dirty and not make a good connection.  The piezo itself is probably fine if it starts working again.

[soundog]

Thanks very much, Charlie .... I'll do that today. 

[psarkissian]

Temperature related,... first suspect would be a solder point oxidizing and failing

somewhere on that signal path. Next I would suspect the piezo itself.

 

Line 6 authorized service tech will know how to deal with it.

 

Piezo electric devices such as watch crystals, system clocks for electronics and such,

are encased and sealed so as to not be affect by temperature. Otherwise, clocks would

not be stable and would drift way too much.

[soundog]

Thanks to you, too, psarkissin. I'll give her a good examination this week and let you know if I see anything. I won't try anything too aggressive yet.

[psarkissian]

"I won't try anything too aggressive yet,..."---

Good. Getting into the piezos on a 700 Acoustic bridge is a touchy thing.

Best left to someone who has done a few. Be careful with the flat ribbon cable

connectors, they're touchy as well.

[Smashcraaft]

@psarkissin: is it okay (and possible) to pull out a piezo for cleaning, using a not so strong magnet on a 600?

Or could there be done any damage to the piezo by changing polarities or something?

 

Others pushed the piezo out a little using a needle or something similar but this means to reassemble the bridge.

[soundog]

The low E piezo was heavily oxidized and "frozen" in place. I noted that the other piezos were free to wiggle about in their sockets. I tried to clean the piezo using some CRC QD cleaner, but the wire was so corroded it just broke off at the piezo end. I've ordered a replacement from Full Compass.

 

@psarkissian - you weren't kidding about the ribbon connector. I could find no obvious way to disconnect it, and may have buggered it. Both the ribbon cable and the pins from the piezo solder board came out of the black plastic connector. I won't know if I did damage until I solder the new piezo in and string it back up. Fingers crossed.

[psarkissian]

@psarkissin: is it okay (and possible) to pull out a piezo for cleaning, using a not so strong magnet on a 600?

Or could there be done any damage to the piezo by changing polarities or something?

 

 

Piezos don't act like magnets, there's no polarity. There may be lattice or cleavage orientations

in the lattice structure of the piezo material.

 

Cleaning, just use a diluted soap based spray cleaner and moisten (not too wet) a cotton swab

and gently go over the piezo with swab.

 

soundog,... if it comes down to it, it may have to come home for some TLC from the docs. There

are of us here who work the earlier acoustic ones.

[Smashcraaft]

Piezos don't act like magnets, there's no polarity. There may be lattice or cleavage orientations

in the lattice structure of the piezo material.

 

Cleaning, just use a diluted soap based spray cleaner and moisten (not too wet) a cotton swab

and gently go over the piezo with swab.

So cleaning has only to be done on the top and not at the bottom of the piezo? The bottom seems to be the part which could cause problems with grounding, isn't it?

[psarkissian]

"So cleaning has only to be done on the top and not at the bottom of the piezo?"--- Correct.

 

"The bottom seems to be the part which could cause problems with grounding, isn't it?"---

No problems with grounding, not with the way the piezos are mounted.

[soundog]

soundog,... if it comes down to it, it may have to come home for some TLC from the docs. There

are of us here who work the earlier acoustic ones.

 

Thanks. I'll keep you posted ... piezos are in the mail. I can't gig 100% without my trusty 700!

[eenymason]

Temperature related,... first suspect would be a solder point oxidizing and failing

somewhere on that signal path. Next I would suspect the piezo itself.

 

Line 6 authorized service tech will know how to deal with it.

 

Piezo electric devices such as watch crystals, system clocks for electronics and such,

are encased and sealed so as to not be affect by temperature. Otherwise, clocks would

not be stable and would drift way too much.

This is interesting. I asked about this same type of problem on a second hand Variax 300 I bought around 2-3 years ago, and really didn't receive much in the way of relevant/possible reasons for the symptoms I was experienceing.

I experienced soon after buying it, the first E and B strings would not be audible through the Pod HD500, although the strings could be tuned using the onboard tuner. I have since realised this odd phenomenon could be explained by the vibrations of those two strings being picked up by the G (and maybe other) piezos. After some time being plugged in, (maybe 30 minutes or so), they would begin operating normally.

I thought the piezos must be dodgy, so replaced the lot with Graphtech Ghosts. This fixed the problem (or so I thought), for a while.....

I now still have the need to plug it in at the start of setting up for a gig, and by the time I'm ready to play, so is the variax.

My questions are, would replacing the PCB fix this problem, and if so, would buying a replacement from Full Compass come to me already flashed, ready for me to simply replace it?

[psarkissian]

Can be touchy devices, but for the most part they do the job well.

Piezos are good transducers of mechanical energy into electric energy,

that's why people like using them. 

[eenymason]

Can be touchy devices, but for the most part they do the job well.

Piezos are good transducers of mechanical energy into electric energy,

that's why people like using them. 

Thanks for your reply - however you must have missed my questions at the end...

My questions are, would replacing the PCB fix this problem, and if so, would buying a replacement from Full Compass come to me already flashed, ready for me to simply replace it?

[psarkissian]

Processor boards come already Flashed, programmed and ready to go.

You would have to specify which Variax, as these are programmed for specific

version of guitar. There is a 300 Electric and a 300 Acoustic, these are

not interchangeable boards.

 

Also, that would depend on availability of the particular circuit board.

 

JTV's,... each has a separate program that is not interchangeable with other

versions of JTV. You can't take a board from a JTV-59 and put it in a JTV-69,

it won't function correctly.

 

And since the topic here is piezos, the early Variax piezos won't fit in the JTV

saddles, and vice versa.

[soundog]

@psarkissin --

 

Update: received the 2 piezos I ordered from Full Compass. I replaced the heavily oxidized one (low E), kept another as a spare. The ribbon cable inserted back in the board connector without too much trouble. Everything is back together and its working great.

 

I'm still not certain what the root cause was. A failing piezo wire (the solder joints all looked good)? As mentioned, the wire disconnected at the low E piezo end when subjected to slight strain. Also, the same piezo looked dirty/oxidized and was "frozen" in its socket. Could that alone have caused the problem? And, if so, is there any preventative maintenance I could do to prevent future problems (such as spraying a bit of silicone on the piezo, etc)? Any guesses?

 

At any rate, I'm very happy to have a fully functioning V700 again for this weekend's gig!  :) 

[psarkissian]

The wire might look good from the outside, but it might have disconnected or intermittent

connect to the piezo element on the inside.

 

Don't spray anything on the piezo. 99% isopropyl alcohol, on a moistened not wet, cotton

swab (squeeze out any excess),... go over the piezo very gently with it.

 

Rock On!!!

[soundog]

The wire might look good from the outside, but it might have disconnected or intermittent

connect to the piezo element on the inside.

 

Don't spray anything on the piezo. 99% isopropyl alcohol, on a moistened not wet, cotton

swab (squeeze out any excess),... go over the piezo very gently with it.

 

Rock On!!!

 

Yes, I think that's exactly what happened. The wire came completely off the piezo, under the ceramic. Good advice on the gentle alcohol cleaning, I'll do that when I change strings.