Compaq iPAQ USB Cradle Charger Modification

by Charlie Reverte, January 27th, 2002

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Have you ever wondered why your stock iPAQ cradle doesn't charge your iPAQ using power from the USB port like every other aftermarket sync cable? Here's how you can modify (rice up) your cradle to do just that so you can use your AC adapter at work or to beat your kids when you get home after a long day. It's a very simple modification if you can solder and if I'm the first one to have figured out how to do this, I'll be very afraid for the future of humanity. It is not hard to do and you can do it in a few minutes if you have some basic tools. I wrote this guide for my iPAQ 3765 so if you have a different model, compare your cradle to the pictures to make sure everything will be ok. I have not tested it on the cradles that come with other models but I think the process should be very similar if not identical for all of the 3600 and 3700 series iPAQ's.

Before you do this, you will need to have:

a fine point soldering iron and solder
some telephone wire (or any other stiff solid core small wire)
a Torx T6 screwdriver
tape
some way to strip off the insulation from the wire (wire strippers, knife, teeth, etc...)
some basic soldering experience

NOTE: After you complete this modification, you should not plug your AC adapter into the cradle ever again while the cradle is plugged into the USB port. If you do this and your AC adapter and your USB port are not at exactly the same voltages, you could have a short from adapter power to USB power. This could damage your cradle, iPAQ and computer. I have not actually tested this to make sure that it will blow up your gear but I am very suspicious, and I'm warning you that it is a bad idea.

I think the reason Compaq made this cradle work off of AC power and not off of USB power is so you could have wall power when you want to upgrade your OS. If you don't have an extra sync cable or a friend with a virgin cradle and you need to sync while running on AC power, you might have to undo this modification or build in a switch to bypass it (very easy, email me if you need help).

DISCLAIMER: If you follow any of the instructions here, you do so at your own risk. Although I believe that this is safe, I have not tested it enough to guarantee that no damage will be done to you or your equipment. You should not attempt this if you are not confident in your surface mount soldering ability.

Step 1:

Unplug the iPAQ cradle from your computer, iPAQ and AC power. Turn the cradle upside down and remove the 4 screws that hold it together. To get them out, you will need a torx T6 screwdriver. Don't try using a tiny flat head eye glasses screwdriver, trust me, you will strip the screws (yes, I stripped one this way). If you don't have a T6, bite the bullet and drop $2 at sears and do the job right. Don't waste your time at home depot or lowes, I went there first and the knowledgeable sales people first thought I wanted a torque wrench and next thought I wanted a torch. I eventually found out that they didn't have T6 screwdrivers. Keep the screws somewhere safe.

Step 2:

Now that the screws are out, start taking the plastic parts apart. This should be very easy to do if you have 2 hands. Remember how it all comes apart for reassembly. Be sure not to lose any of the springs. The part you are interested in is the little circuit board that plugs directly into the iPAQ serial port when it rests in the cradle. This is the green board with the black socket and USB cable connected to it. Free it from the slot in the cradle so you can work on it. Be gentle when you handle it because the USB cable wires can easily break off of the board (this happened to me). It's an easy fix if it happens but it's better to avoid it.

Step 3:

The goal here is to run a single jumper wire between pin 1 of the serial port socket (the pin all the way on the left marked 1 on the circuit board) and the red power wire coming out of the USB cable (marked H2 on the circuit board). This will connect the iPAQ to USB power so you can charge the device without the AC adapter. I found that solid telephone wire works best for this step (you can also tear up some ethernet cable). The reason I like telephone wire is that unlike braided wire, it is stiff so you can bend it into the desired path and it will stay there. This makes holding the wire in place very easy for soldering.

Since the pin you are connecting to on the serial header is very small, the best way to solder the wire is not to line it up and drop a blob of solder on it. This will probably end up connecting some of the other pins together which you don't want to do. The easiest way to make the connection is to strip the insulation off of the ends of the wire and tin the ends with solder. To tin the wire, put a small blob of solder on the tip of your soldering iron and pass the tip of the wire through the molten blob a few times. After you get a nice even coat of solder on the bare end of the wire, tin the other side and wipe off any excess solder from the tip of the soldering iron with a wet sponge or paper towel. Bend the wire as shown with a pair of small needle nose pliers and tape it down. To make the connection, put the soldering iron on the top of the wire until the heat conducts through it and melts the solder coating between the wire and the pin. Once it melts, remove the soldering iron and it should freeze in place. Do the same to the other end of the wire. Test the continuity with a multimeter to make sure your connection is ok.

Step 4:

Now, just put everything back together and hook up the USB cable to your computer (DO NOT plug in your AC adapter) and plug in your iPAQ to see if you get a yellow power light. If it's charging, you're all set. If not, take it apart again and verify that your solder joints make a good connection. To make sure that I didn't forget and accidentally plug in the AC adapter, when I put the cradle back together, I didn't put the AC adapter socket back in properly. I left it loose inside the cradle casing and turned to the side so no one could possibly plug it in by accident. Good luck and email me if you have any questions. --charlie

Additional Information:

I was stupid and looked this stuff up AFTER I got this working...

iPAQ Communications Port Pinout:
(from http://www.handhelds.org/Compaq/iPAQH3600/iPAQ_H3600.html)

Pin	Name	Description
1	V_ADP	AC adapter power in
2	V_ADP	AC adapter power in
3	DTR	RS-232 Data Terminal Ready
4	GND	Power ground
5	CTS	RS-232 Clear To Send
6	RTS	RS-232 Request To Send
7	TXD	RS-232 Transmit Data (from the SA-1110)
8	RXD	RS-232 Receive Data (from the SA-1110)
9	DCD	RS-232 Data Carry Detect
10	GND	Power ground
11	UDC_P	USB positive data signal
12	USB_N	USB negative data signal

USB Connector Pinout:

Pin	Color	Signal
1	Red	+5V
2	White	Data-
3	Green	Data+
4	Black	Ground