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B-Band A3T tuner/Preamp drains the 9V battery overnight

Pleased to present for your consideration. . . . . . . . .

Also, I'm a hobbyist, not a professional repair person.   

One of my guitars came equipped with a B-Band A3T tuner/preamp with a under the saddle pickup.  I'm guessing it's 10+ years old.  It's a system that has both the Hi and Low output options.  It's powered by a 9V battery.

It has started to discharge the 9V battery overnight without a guitar cord being plugged in.

With a good battery installed the tuner and the preamp work properly when the guitar cord is plugged in.  The tuner works properly with or without a cord plugged in.

But if I don't remove the battery, it will drain overnight.  I've run this test 4 times, 3 with partially used batteries and the 4th time with a new fully charged battery.  Each time the unit works as designed when the battery is installed, but the battery is drained in the morning.

The 1/4 inch output jack has 3 connection points, ground, tip and a middle contact tip that contacts the ground shaft of the plug.  I've wired these female connections before on guitars that had only a preamp, and the mid contact was used to complete the connection to the ground side of the battery when plugged in. Acting as a switch breaking the battery connection when the plug is removed.

But this unit is designed for the tuner to be functional with or without a cord plugged in. So power is always available to the tuner.  Is the mid contact strictly to power the preamp?

Note on the top picture that there are four contacts for the plug in connector (white) cable that goes to the preamp box.  Bottom to top they are identified as GND, OUT, SW and B+(?)

First guess would be, ground, output (tip), switch(power to preamp and low output circuit) and B+ being constant voltage to tuner.

For the 1/4 female connector, looking again at the first picture starting at the left side of the 4 way white cable connectors going clockwise, the tip contact, ground and the middle contact.

My meter is non functional, and I'll need to pick up another Monday so I can't get readings yet of the 3 contact points on the 1/4 output jack, or how they relate to the 4 connector cable contacts.

Anyone have any experience or suggestions on how I can test for this power drain?

Thanks in advance.

John

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After mulling over this issue for 3 hours last night, going to bed thinking about it, getting up in the middle of the night and writing the post, going back to bed, laying back down thinking the last cable connector, B+,  the answer may have come to me.

Battery, positive connector.

IF that is correct, maybe this could be the layout of the connector. 

GND and B+ would power the tuner always on.

GND and SW would power the preamp.

GND and OUT would be output.

I'll get a new meter today and can check voltage across the connectors.

Let me know if this makes sense, or if I need to go back and sleep on this again.

Back with some meter results.

The connectors were as I described above.

With a battery installed:

I get voltage across the GND and B+ constant, with or without a cord plugged in.

I get voltage across the SW and B+ with the plug in, no voltage without the plug.

The 1/4 inch output jack seems to be working as designed.

For my next test, I'm going to install the battery and leave the output unit disconnected from the internal harness and see if there is a voltage drain.

There is a spring loaded button switch at the base of the Low output jack with 2 wired in switch circuits, both are complete circuits when NO Low plug is installed.  Open circuits when a Low plug is inserted.

More latter.

Next update.

Left the battery in overnight in the output unit un-cabled to the interior preamp.  No voltage drain.

I have to remember that I messed with the mid contact point, forcing the angle back when I thought it was contacting the ground sleeve of the 1/4 inch output.

I'll update again in 6-8 hours and report on the result.

If it drains the battery again, anyone have any suggestions on what to look for next? 

Next update.

The unit held power for the last 17 hours connected to the preamp box.

Next, it's going back into the case, which is a very good, snug fit, and where I put it for the initial tests that killed the batteries.  I'll see if any pressure is being put on the tuner on/off push button.  Maybe it turns that function on for it's 2 minute unattended cycle, and drains over night.  I don't think so, because all the preamp pots have knobs that are taller than the on/off button and they seem to have a little extra room in the padding.

Looking more like I may have solved it possibly with my tinkering constantly with the mid point connector in the 1/4 jack and manipulating the button switch at the bottom of the low out jack which could have been powering that unit before I replaced my meter. 

Another example of trying 2 things simultaneously, so you can't isolate which one solved the issue.

Live and learn I guess. 

From the last report on Wednesday to Saturday morning, the battery has died enough not to power the tuner or preamp.  Checked it every 12 hours or so and could see the voltage dropping at the battery.

Any suggestions where to try next?

I'm going to poke around the button switch at the bottom of the low output jack and see if it's powering just that part of the circuit in the unplugged mode.

Does anyone know if that board is only powered on when the low output jack is engaged?

Or on constantly as the preamp is powered up, no matter which output is chosen.

Thanks in advance.

I notice a tuner button on the interface. Is it possible that it's in the on position and constantly draining the battery? 

How about that SW connection on the jack, could it be shorted in a way that powers the preamp?

Also, do you have access to a scope? It would help tremendously to troubleshoot this.

Most preamp systems will only draw current when a mono plug is inserted into the jack.  The jack is a 3 contact stereo type that has the battery negative lead connected to the middle (or ring) contact.  There are variations on this theme but I'd suggest the following path:

1. You have two jacks.  I suspect that only one of them switches the battery and that one is defective and will have 3 wires (as opposed to two) attached to it.

2. If they are a closed endpin jack type, consider replacing them.  The closed jacks are great but when they fail - there are no repair options.

3. Check the battery clip or compartment for shorts and corrosion.  If you have had a leak, the residue is conductive and may be draining the battery.  Clean it up with a toothbrush, brass wire brush and q-tips soaked in Isopropyl Alchohol

4. Look for shorts in the wires going to the jack.

5. Make sure the leads on the back of the jack and wires attached to them are not touching.

That is a start and stops short of disassembling the preamp and looking for other issues.  The root cause of battery draw problems are usually pretty simple.

Best regards,

Jeff

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