Introduction: Double the Battery Life of the DX3 Radio From Spektrum for Under $20
I first got the idea for this over on the thread for the DX6/7 on RCGRoups.com forums. I run nitro cars, so I bought a DX3. I used the radio for a while, and my battery life was on the better side of most radios--but the DX7 owners were getting like 5-6 hours of runtime after the mod. Now that's what I'm talking about! I figured that the DX3 and the DX6/7 might be using the same regulator chip, due to the fact that the chip design and internal circuitry shoulden't have changed that much. Less PCB tooling and all that.
Turns out, I was right.
I would harbor a guess that the DX2 (new and old) use the same regulator inside. However, I have not tested those and the innards may be a little different. Check your parts, and make sure your soldering it in the right way. Best case, it doesn't work. Worse case, you release the factory-packaged smoke and you get to buy a new radio. Not fun.
The mod is about as easy as it can get: De-solder a component, tin the pads, put the other component on. Done.
Here's a picture-by-picture diagram on what to do. As with everything on the Internet: I take no responsibility on your actions. This worked for me. It may not for you. Don't do it if you can't solder.
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Step 1: Assemble Your Tools
Step one: Assemble your tools. As with any good mod/hack, get your tools together before you start modding. Also a good rule for life, I suppose... At any rate, I ended up using:
Needle Nose Pliers
Solder, sponge, etc.
Step 2: Removing the Back Case
There are 8 phillips screws, as indicated in the picture. Remove them. You do not need to remove them all the way from the case if your good. If you don't think your skills can pay the bills--remove them, and put them somewhere safe. Preferably inside something you can close so they won't scatter under the workbench. If I had a nickel for every screw I lost...
Also, you will want to be very careful about the antenna wire, which is attached to the antenna which is attached to the back of the case. I don't know why (I think it's an engineering flaw, myself) but such is life. It's very thin and fragile. Well, it's not really that fragile but you can break it if you gorilla it too much. Just remove the back and you'll see a grey wire going to a small golden connector on the PCB.
Using your fingernail, put it just under where the wire meets the connector at the PCB, and pull straight up. The connector will come off easily (if not, don't force it! just wiggle it and it will pop off) and then put the whole back case off to the side. See how you don't need to remove the screws? I told you I was good...
Step 3: Find the Linear Regulator
It's pretty easy to spot... It's pretty much staring you in the face. Its the black square with three legs next to where the antenna was connected, and right above the bind button.
About the bind button... It's kinda right in the way of where we are going to be working... but you can't remove it. You may want to put some layers of tape on it so you don't end up melting it. I only singed it a little, but it still works. Plus, it's not like anybody sees it anyway...
Step 4: De-solder the Linear Regulator Legs
First, you tin up the legs. All electronics sold in the USA have to be RoHS Compliant. What that means for us is that there is no lead in any of the solder. That means that it sucks for re-soldering. So tin up the legs with your new solder. Just because they can't be sold in the USA without being RoHS compliant dosen't mean that we have to use use PBFree Solder. (PB is the symbol for Lead.)
Now wedge your needle nose pliers under the first leg and gently pull up on it while putting the iron on the leg. You will hear it pop (or make a scrunchy sound.) which is normal. At this same time, you'll see it move up. DON'T PANIC. Just keep a firm grip on the leg and move it up and out of the way.
If you got a big solder-bridge, two things may have happened:
1. You had too much solder on the leg.
2. You didin't move the leg up enough.
Just heat up the solder and with any luck, it will come free. If not, get out your solder-sucker and suck the excess solder up. If you don't have a solder-sucker then just wipe off the tip of your iron and wipe it through the solder. And get a solder-sucker. Soon.
Step 5: Removing the Linear Regulator From the PCB.
This involves heating up the bigger end and melting the solder under it. It is a seperate step, because unless you de-solder the legs first, you'll never get the unit off the PCB.
The PCB is the heatsink for this part. And, I did some tests with my temperature probe--this sucker got HOT. All that wasted energy as heat means your batteries are going bye-bye. To remove the regulator, simply put your iron on the large flat metal piece and feed some solder into it. Push up against the part and you'll likely send it flying across your workbench. Don't worry--you shant need it again. Let it keep the dust bunnies company with it's radiating warmth and lack of efficiency at high voltages. They'll appreciate the company.
Step 6: Tin the Regulator Pads on the PCB
A small step, but a crucial one. Without this step, you'll have a very hard time getting the new regulator on the pads. Trust me. I hate PBFree solder.
Step 7: Inserting the New Regulator Into the Circuit
This the only really, truly difficult step. And even this one isin't that bad.
There's not enough room on the PCB to have the new regulator fit where the old one was. There is also not quite enough room to have it sticking over the edge. What to do! Luckily, we do not live in a flat world!
My solution is to slightly angle it and have it up in the air. Good for cooling (the regulator hardly gets warm at all--also tested) and more importantly: It lets it fit!
Tack down one leg (making sure to check the polarity) by pressing the iron to the leg and NOT the pad. As you should all know, you heat the component not the solder.
With the extra solder already on the pad, once the leg heats up it should flow easily and stick the component down. Ah, good old lead solder. Then solder the other leg, and then the other-other leg. Easy.
I had to clip off a little of the legs to make it fit without touching the ground-plane. That's the big silver area where the old regulator used to be. You may not need to. Just don't let them touch the ground-plane that the other regulator was stuck to. Sparks and the factory packaged smoke may be released. BAD!
Also, you could also use a little bit of wire and stuff it down into the body of the radio. I don't like things rattling around inside my radio--so I chose not to do this. You make your own decisions, and stick with them.
Step 8: Testing the Regulator
Put a little more solder on the legs of the new regulator, and make sure that all connections are good. I do this by putting my DMM into Diode/beep mode and I touch the leg of the component near the component, and then another component that the trace runs to. On some circuits, this is easier said than done--but it is super easy on this one.
The two capacitors on each side of the old regulator gets a nice big trace to it. Simple touch the one probe of your meter to the regulator, follow the trace to the cap and touch the probe there. If it beeps or shows Zero-Ohm then your golden.
Next we get to test the radio. Turn on your receiver (RX) and wait for it to go into failsafe (3 sec). Then take your radio (TX) and put in the battery pack. You'll have to hold it in, as the bottom won't fit anymore.
Don't bother with the antenna or screwing on the back--just leave it off for now. Hold in the battery pack in and turn on the radio. Look at the display. Does it show a normal voltage between 11v and 10v? If it does, turn the knob and pull back on the throttle. If stuff moves, then your golden. Turn off the radio and the receiver, and put the battery pack off to the side once again.
If it dosen't, make sure your battery pack is charged and that you have it put in the right way. If it still dosen't work, go back and test your connections again. If it STILL dosen't work, then remove the regulator, clean the pads and the regulator legs of solder (solder-sucker!) and put new solder on.
Step 9: Putting It All Back Together
Take the antenna wire and find the connector on the radio. Yes, I know it's very small. Yes, you can do it. If I can do it with my big, fat fingers--you can too.
It's kinda tricky, but not too bad. The trick is getting it right over the connector. Put your pinky, or whatever you can under the floating PCB in the TX. Push down on the connector (gently!) and it will click/snap into place. Honest, it's a feather-touch here.
The connector will spin without popping off when it is on properly. Just don't go spinning it around in a circle like a goober. Once the antenna is back on, put the clear plastic bind button onto the LED that's sticking out of the black button, and put the case back on. If you angled your regulator correctly, you should be able to put the case back on and screw in the screws easily. If not... well... Go back and put it on correctly.
Don't go bending it like a hosehead either. You'll rip off the pads and then you will be up a certain creek without a paddle. so just don't do it. Re-soldering takes a minute, and it's easy.
Step 10: It's Over!
Step ten: Sit back and feel accomplished! You did it! Now your batteries will last a LOT longer than they did before. I don't honestly know about how long they will, but it's noticeable.
I have 2600Mah batteries in there now, and before they would drop from 11v down to 9v really quick. I'd say, a good 2 hours of hard driving would really put a serious hurting on them. And alkaline batteries were almost useless--going dead within a matter of minutes. Now I charge up my batteries, and I can go all day without fear of my batteries going dead on me. I ran out of fuel before I ran out of batteries in my radio!
The RX on the other hand...
And before you start asking questions: No. The RX won't benefit as much from the new regulator as the TX does. The reason is kinda compliecated, but basically the old regulator was horribly inefficient at taking high voltages and stepping them down to the voltages that it outputs. This one output 3.3v and as you can see the batterpack has 8xAA batteries.
8AA * 1.2 = 9.6V (Ni-MH)
8AA * 1.5 = 12v (Alkaline)
Since the output (3.3v) is more than double (triple) than the input voltages, the inefficient regulator just burns up the batteries as heat.
The new regulator that we put in is a switching regulator, which has very high efficies at almost any voltage. Plus, it uses less current to operate. A bonus all around!
Step 11: Notes and Afterthoughts
There you go! I hope this helps you as much as it did me. For as easy as this is, there is really no reason not to do this. I mean, other than the fact that you may break your radio... But that's never stopped me before! If anybody else comes up with information, or I need to change something I will make a note of it here.
And here's a video of it working. Why? Why not! Enjoy!