Turnigy 9xV2 battery mod problem

[av8nmac]

I need some sharp electronic type guys to help me figure out my problem, here goes: I did the mod, hooked everything back up, powered the tx and everything looked good at the beginning. Then after about 20 seconds the displayed voltage started climbing from 10.2 to 13.6 volts. It stopped at 13.6 v and occasionally the voltage display will flicker all kinds of voltages and usually settle on 13.6v . Any suggestions where to start troubleshooting will be appreciated . I'm hoping I did not damage a component will soldering, even though it took little heat to connect the resistor in place.

Thanks,

Paul

[RCModelReviews]

You need to check that the resistor is soldered to the correct bits of the circuit board (can you take a picture).

[av8nmac]

Here is a pic of the resistor. Could residual flux cause my problem? Maybe a cold joint? Also, when I powered it up today the voltage started at 10.3 and after a minute or so started dropping to below 6 volts.

Again, thanks for your taking your time to help me out.

Paul

DSC01062.JPG (99.25 KiB) Viewed 10461 times

[RCModelReviews]

The circuit we're dealing with here is simply a resistive voltage divider so one of two things must be happening..

1. one of the resistors (or a connection) is changing in value. Looking at your picture, is it possible that the solder joint at the top has pulled away slightly (looks as if there's a dry area on that solder joint).

2. the MCU is not reading the voltage correctly for some reason.

I'd put a volt-meter on the resistor you've soldered in and watch the voltage on that. If it rises slowly (in concert with the display) then there's a problem with your soldering or a component affected by the soldering.

[av8nmac]

Bruce, is the trace right above the 512 resistor connected to the 512 resistor? I originally soldered the 8.2K resistor to the end of that 512 resistor and not to the trace above it, did I place the 8.2k resistor in the wrong place?

Thanks,

Paul

[RCModelReviews]

You're actually trying to solder across the 512 resistor but because these are such tiny devices, it's easier/better to solder to the copper as I pictured it. Put your multi-meter across the resistor you've added and make sure that the voltage is fairly steady.

If you tried to solder to the resistor itself you may have damaged it -- but that's unlikely.

[JMP_blackfoot]

From the symptoms given above (voltage slowly drifting up or down) I would start with cleaning the general area with a toothbrush and acetone to remove all soldering residues.