If you read my post regarding the NMEA GPS script where I tested a new GPS module I bought you will recall that it has a minor problem. It was drawing 3x as much current as it should!!! So, not good. This first step in solving the mystery of the too much current was to remove the shield from the bottom of the module. The shield has solder points on all 4 sides, fortunately only 2 where actually soldered well. I removed it by fluxing the solder joint. Heating it up with a big wave tip with a lot of solder on it. And wedging the tip of an X-acto knife under the shield and torquing it. The shield popped off and I could see the guts of the module.
How to figure out where the problem lies? Well it was noticeably hot so I put one finger tip on the top of each chip, plugged it in and waited. It was only a few seconds before I was greeted by a warm sensation on my index finger that was pressed against the upper right sop package. Closer inspection revealed the part number to be ZT3221LEEY. The datasheet showed it was a RS232 level converter. I will only be using the TTL output voltages in any project I use this module for and thus had no need for those signals. A simple RS232 level converter bypass was all that would be needed to lower the current consumption of the module to a reasonable level. I decided to go with the easiest method of disconnecting the chip. Slice the VCC trace that connected to the module. A quick look on the data sheet showed that pin 16 was the VCC pin.
Taking a closer look at the chip with the magnifying glass I saw that the VCC trace simply came down from a capacitor just above.
A little bit of scratching at the trace with an X-acto knife and I checked the continuity between the capacitor and pin 16 with a meter. It was severed.
I plugged the module back in with an ammeter attached to see if the issue had been resolved. I was ecstatic to see a reading of only 30mA! The current draw had been reduced 6 fold and this module would be worthy of use in a project.
Finally, the most deceptively tricky part lay ahead. Reattaching the shield. My first move was to grab some desoldering braid. I pulled all the excess solder from the holes that held the shield in place with a bit of flux, the wave-tip, and the braid. Once I was satisfied with the cleanliness of the gold plated pads I cleaned the flux residue from the surface with some isopropyl alcohol. Placing the shield over the module and pressing it down into the holes it would not slide in all the way. I put some needle-nose pliers around it and squeezed lightly while pressing the wave-tip to the shield above the pin. The extra solder keeping the pin from sliding in melted and the pin slid in. I repeated for the other 3 pins and the shield was cleanly attached.
Shiny and ready to rock!