GT3B Voltage Regulator Mod for $0.60

[Hydrocarbon92]

I finally got around to doing the firmware hack on a freebe GT3B I got a while back. While opened, I decided to also look at changing the linear regulator. The 78M05 was 40% efficient at best, and now it's in the 80-90% range. I also saved $11+ over the "drop-in" switch-mode regulator I've seen elsewhere.

First you need to pull it apart. There are several guides to opening this transmitter, it's basically 4 screws on top and 2 unseen tabs on the long sides. Squeeze the 2 sides of the lower shell under the face and pull on the face gently.

Then I took the $0.60 MP1584 I got direct from China (I actually get them in lots of 5+ for $0.30 or less). De-solder the original reg, or just cut the legs. Solder wires to the MP1584's IN+, OUT+, and either IN- or OUT- (ground is shared). The regulator leg/hole closest to the black screw is IN+, the middle is Ground (IN- or OUT-), and the leg/hole closest to the power button is OUT+. Connect the wires accordingly.

Last you simply secure the regulator, seal the radio back up, and power it on. The voltage monitor works like normal too! At this point you can also switch to lipo/etc batteries - this reg will accept 2S to 7S, although 3S would keep the stock voltage monitor settings happy.

Word of caution: these regs are usually adjustable, and many aren't set to 5.0v. Mine were set to 6.0v, so you should test it out first. There are some other fixed 5v regs, usually with USB ports on them, so you can save yourself some effort with that route.



Here's the large pic if you need detail:
https://i.imgur.com/c9DFQIW.jpg

Here's a link to Aliexpress for this type of regulator, although they're also sold on ebay & other places. They usually contain "lm2596" in the name since that's a very common regulator they replace: https://www.aliexpress.com/item/1PCS...StoreLevelAB=5

BONUS: you now have a cheap source for a 2A cont./3A peak UBEC! I use these on all sorts of projects. The MP2307 is smaller & efficient, but the MP1584 usually offers smoother power output.

[Bbknucks]

Nice work. I have a gt3c I would like to update. Even though I don't need the extra channels...yet

[dweano]

Gt3C does not need this mod. It has an efficient regulator already

[Hydrocarbon92]

I believe the GT3C is just 3.3-5v tolerant, meaning it can run on power in that range. That's how it can use a 3.7v battery but still work fine with a 5v ST-Link programmer. That'd explain why my GT3C battery lasts so long despite being a 3 watt-hr battery vs the GT3B's 24 watt-hour 8x AA's.

[Bbknucks]

I was referring to the updated firmware.

[Hydrocarbon92]

I updated the GT3C at the same time, only oddity was the voltage. Since you use the B firmware, it shows 3.7v as 9.6v but that's easy to change in the CAL menu.