I'm thinking this is a fairly common issue, but I don't have the experience to confidently fix it while feeling certain I won't do any damage to the setup that I'm using.
I have a brand new EQ-7545R Piezo Pickup / Pre-Amp Unit that I just put in a pretty cheap but good sounding cutaway acoustic six-string guitar that a friend gave to me. The original Piezo pickup under the saddle just stopped working because of the wiring, which I tried to fix by soldering, but was unsuccessful.
So I ordered the new one through Amazon, and it was in brand new condition, and actually worked after I first put it in. Now however, the (under the saddle pickup) only works intermittently, and I feel that I've narrowed it down to be (possibly) either an issue with the saddle piece, or the piezo pickup sliding loose enough under the saddle piece. After detuning from (for example) standard tuning to a drop-D or an 'open' D tuning, the pickup would work at first, allowing me to hear everything I would play amplified, but then dropped out to a point with no sound whatsoever. When the pickup was actually transmitting the noise of the strings to the amplifier, the preamp functioned normally as it should. So I loosened up my strings to a point where I could remove the saddle piece and test the piezo under the saddle pickup by tapping it (while amplified) to see if it was defective, but the sound came through. After then putting the pickup back under the saddle, placing the saddle piece over it, and retuning to either standard or open tuning, my sound was amplified temporarily, but then once again lost all sound within a matter of minutes. After this occurred, I would tap on the saddle piece in between the strings, and that sound was amplified clearly, while strumming on the strings was not.
So at this point, I have just loosened up the strings, and have removed the saddle, in hopes that it may be something as simple as needing to replace the saddle itself, possibly with one of a different material (the current one is plastic); or maybe just putting something between the piezo pickup itself and the very tiny space between where it's positioned and the inside of the slot/space. It crossed my mind that maybe something like a bone saddle, or just a new plastic one altogether, may make a difference; but I want to reach out to whomever has heard of or dealt with a situation like this. I really just want a dependable amplification for this acoustic, in hopes of being able to use it for recording and open mics. I look forward to hearing back from anyone who may have tips, suggestions, or solutions.