[HD2 General] motoi_bogdan:
i've completed my work on the third hd2 with thermal problems that i had for repairs. It's now 100% working, including those previously dead volume buttons and front buttons. They are now all working.

But let's rewind a bit.

Yep this one had some button problems. As hard as i tried, the volume button just kept being pressed by it's own, even if i removed the whole flex cable with the camera, volume button board and etc. So like i've said before about measuring voltages on the volume board and it's buttons, here is a fix that i found for my problem.

1. solder 3 wires on the volume board for easier measurements.

it's kind of hard to distinguish what wire goes where from that picture but.. in my case, red is point A from "UP" volume button, black is point A from "DOWN" volume button and blue is point B from any of these 2 buttons, you can choose whatever you want.

In a normal phone, you should measure about 1.4 volts from point B to any of the A points. Let's say the + volume doesn't work.

2. Disassemble the flex cable containing camera module, volume buttons and wifi/motor small board (the one with the connectors). On the backside of the wifi/motor board we will see the light/proximity sensors and the orange/green led's. That's the area were we are focusing. We want to tap into the green led's current limiting resistor, because the green led junction has the property to begin lighting up at 2.3 volts and act kind of like a zenner diode for the circuit we're trying to adjust. We need that voltage for biasing the transistors inside the snapdragon chip that control the volume function. It just happens that they also use about 2.3 volts to signal volume idle state (no button being pressed). Here's a photo with the small wifi board. You want to turn it around and solder a small wire in the small copper pad signaled with the red circle.

Careful not to touch either the led's or the sensors with the solder iron's tip, they are very fragile. Also careful not to solder on another copper pad, these contain various voltages, we don't want to.. mix things up with God knows what results.

3. partially assemble the phone in some state that will allow you to turn it on.

here's my ... "setup". now, either in magldr (it requires volume buttons to operate) or in your OS, look to see if by touching the wire you soldered to the wifi board with one of the wires from the volume board, you get some result - a volume up/down command, something like this. Also, try various combinations, i found them to be safe if you soldered at the specified locations. Try "pressing" a button by short circuiting one A point with a B point (corresponding wires) while connecting them with the wire from the wifi board, near the led's.

4. there are possible scenarios. If you don't get any kind of success by doing this, then it's clearly that at least 2 volume pins have a broken connection to their corresponding bga balls underneath the snapdragon chip. This can ONLY be solved by either reheating or reballing that chip.

If you manage to use the volume buttons by connecting their wires to the one you placed near the led's, then you have only a single pin broken underneath the snapdragon chip. I would not risk reheating in this situation. This is what happened to me with my last HD2, i fixed by this way, i left it like that. If you manage to make even one single volume button, it could be enough as you can operate either magldr or CLK with one of them. It's some sort of good compromise solution.

About the buttons underneath the display (call buttons, home, back, menu keys). In my case i found out that 2 of them were not working. Today I found out why. I suspected the CPU and it's soldering again, but it seems that's not the case. The problem was located (in my case) to the crappy button flex cable and ...equally crappy motherboard connector. I cleaned both of them with some alcohol and after some 8-9 attempts to reconnect them, i found out some sort of a position in witch they seem to work. During my attempts i some time thought i connected them properly but for whatever reason they didn't seem to work. It seems the flex cable design is pretty awful, they are veeeerrrry sensitive to placement position. I, personally i would have preferred a double layer connector. Anyway, if you want to make sure the motherboard connector is working (and you have a flex cable placement problem) you could again partially assemble the motherboard and display to the battery and attempt to start the phone by simply making a short circuit with a metallic object on the small pins on top of that motherboard connector. It's safe to touch them together, they use low voltage, there is no risk involved as long as you only touch the connector and not anything else on the motherboard while using the metallic object. Simply move the metallic object along those pins for 2-3 times, trying to short circuit 2-3 pins at a time. If the connector is good and the snapdragon chip's connection are good, the phone should start. If NOT ... then again, it draws back to reheating and such stuff.

It's a bit difficult to service system on a chip designs like this snapdragon chip and it's board. Back when i serviced ipaq pda's, there was one chip for about each function of that motherboard. If something was not working you could simply locate the corresponding chip and either measure what's going on there or replace it. HD2 has all those functions (including wireless transceiver, gps receiver, cpu, io controllers etc) included in one single chip, that snapdragon one.

About using paste (i guess you're pointing to that flux paste) to reheat... well, i didn't use any. It would be helpful if you have removed the chip itself and you're resoldering it back. But i STRONGLY recommend caution about this. There are veeeeery little chances of success or getting the chip to work again if you remove it from there and try to resolder it. The best thing to do is to very carefully reheat it. If you get to a compromise were you get best results with as little lost functions (one not working button, stuff like that) leave it like this and try to live with it, don't risk yet another reheating session.

Here are my 2 repaired tmous hd2's ... and the one eu HD2 that passed away (scattered around).

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and their backs.. they do look like, well, crap.. but once the battery cover is placed, they look like any regular hd2 and while they are doing their jobs i cannot complain. Both are running at 1198 mhz, nandoid (i happen to have developed a crush on 3d gaming on mobile phones :D )