Manual: Maintaining and modding the HTC Desire S

This manual lists all the steps, in logical order, to go from a physically broken phone to a great working, free and open source phone. It links to several other articles on this blog for detailing individual aspects.

Hardware

(1) Getting your hardware repair tools ready

Please see the corresponding section in my HTC Desire HD manual.

(2) Identifying hardware defects

Symptoms, by broad symptom, then split into sub-cases. This only includes symptoms for which I had at least one practical case. So of course it's an incomplete list.

1. Cracked screen glas.
   1. Cracked screen glas, touchscreen works, display works. It is sufficient to just exchange the touchscreen digitizer unit, but it involves re-glueing it to the screen unit.
   2. Cracked screen glas, touchscreen does not work, display works. It is sufficient to just exchange the touchscreen digitizer unit, but it involves re-glueing it to the screen unit with small stripes.
   3. Cracked screen glas, touchscreen does or does not work, display does not work. Fix: Exchange the complete touchscreen and display unit. That saves you work, as you don't need to separate these both.
2. Does not power on. 
   1. Water damage. Aas indicated by the water indicator or by what happened to the device. Fix: Immediately dry the device by storing it in rice for some days. Exchange the main board. If display is also affected, you need to also exchange it (but maybe can keep the touchscreen unit).
3. Sweeping sound when plugging in or powering on. A high-frequency sweeping sound of ca. 0.5 s duration. In case of plugging in, it only apeared when the phone was off. Diagnosis: bad connection of earpiece speaker. It probably has only one of its two contacts connected, the other might be bent. Fix: Bend earpiece speaker contact to correct postion. Else, exchange earpiece speaker. It can be pushed out from the front after disassembly to the bare screen unit.
4. Touchscreen problems. 
   1. Intermittent touch button function. Sometimes, the touchscreen will work, but the touch buttons will not. Putting the phone into standby and waking it up again (by pressing power button twice) can fix this for a time, and it mostly stops working at one of the nest wakeups from standby or reboots. Flexing the phone durng standby, or better compressing the display unit in the touch button area somewhat, will help to fix the problem more often on wakeup. But since the display unit is a closed unit with too much space below the touch buttons to compress the contacts, this is not a well-working recipe. Diagnosis: Connection issues at the flex cable's glued connection to the touchscreen film. Alternatives may exist. In my case, this happened when I accidentally lifted a bit of the glued touchscreen film before mounting it as I though there has to be a protection film as my other touchscreen spares. Fix: Replace touchscreen unit. (It may also be possible to repair the affected connection with conductive glue or similar; I did not try that yet.) Note that, from looking at the touchscreen construction, it seems that the touch buttons are just part of one big touchscreen area and will be interpreted as buttons by firmware, not by the hardware. The touchscreen buttons might be more sensitive to malfunction because of (probably) an added software test on wakeup for iniializing them, but if you have problems with them, it's also probable you have other touchscreen problems as well.
   2. Intermittent touchscreen function. The symptoms are the same as with intermittent touch button function, just that this time, the touchscreen itself will either work or not work at all. It is however most often fixed temporarily by a standby cycle. Diagnosis: Connection issues at the flex cable's glued connection to the touchscreen film. Alternatives may exist. Fix: Replace touchscreen unit.
   3. Top line-shaped area of touchscreen stopped working. Diagnosis: Connection issues (loose contact) at the flex cable's glued connection to the touchscreen film. Or a broken wire connectiob that is responsible for the top part, of the touchscreen's printed circuit. It was not clear in my case. More alternatives may exist. Fix: Replace touchscreen unit.
   4. One point of the touchscreen does not work. This might be as small as one letter of the keyboard, while all other areas of the touchscreen work flawlessly. Diagnosis: Touchscreen broken. No more detailed explanation at the moment. Fix:  Replace touchscreen unit.
   5. Intermittent touch button lighting. They should normally switch on right when you wake up the device from standby. Or maybe not and this is controlled by the ambient light sensor? Because they would sometimes switch on some seconds later, sometimes not at all (tested inside, artificial lighting.) Diagnosis: None yet. But might be a software-caused side effect of a malfunctioning touchscreen, which was present at the same time. Fix: None yet.

(3) Repairing hardware defects

• Complete screen unit replacement. See How to replace HTC Desire S LCD screen, which is a special disassembly video for this task.
• Touchscreen replacement. This is quite a difficult operation. My unfinished set of experience values:
  • Wear protective glasses when pulling off the damaged touchscreen. Glas splinters may fly around.
  • Be very careful when pulling out the damaged touchscreen. Be sure to read through TechRadar: How to fix a broken touchscreen, which are the best instructions for the heating part as per my experience. You have to heat the touchscreen edges to ca. 60° C, then pull or push out the touchscreen slowly. The best idea is to start at the lower edge, pushing with a plastic pin through the button backlight holes [video]. I then use a safe open pry tool to go along the edges and slowly pry it open. If you do not heat it before, and pull with too much force so that strong pull or shear forces occur, you will damage the display itself beyond repair by pulling apart its internal makeup from films. This happens because the narrow glue stripes around the touchscreen are attached to plastic film that is glued to the back of the display and then wrapped around its edge, and also glued to its front. If the glue is not melted enough, or esp. if this wrapping film ruptures at the edge but keeps sticked to the screen, pulling out the touchscreen will exert too much force on the display's surface, and pull apart some internals. This results in large blackened screen areas, which shrink temporarilywhen pressing on them (showing that the defect happened by pulling some internal layers apart).
  • It is possible to identify displays which have been damaged in this way when pulling the touchscreen off. Normally the display has a complete uniform color, but the borders of damaged areas will appear in greenish or reddish color when watching the reflection of a light source in the display. This test is only possible when the touchscreen is not mounted, as the color differences are barely noticable. But, when testing the display with a working phone before the touchscreen replacement, and then ensuring that the display has not been damaged by pulling the touchscreen, you prevent the unnecessary work of finishing this "repair".
  • You have to pull off the four little light-guide elements for the touch buttons, and re-glue them to the new touchscreen as this is not part of spare parts. For that, you may need a template built from a broken display unit's frame, or (less optimal) you can place them into the receptives on the display unit with the glue side up. I do glue them all on a common stripe of double-sided adhesive though, not four individual ones as in the original.
  • Remove protection film carefully. When buying a spare touchscreen, there is normally a protective film on top, and sometimes also one at the bottom. These are just sticky, while all other layers are glued. So be very careful to never try removing a bottom protective film when there is none. I damaged two touchscreens of me by lifting the glued flex cable contacts, as there was no protective film to lift resp. it was hard to catch. The best test is to use a small screwdriver and to try scratching very slightly in one corner and comparing with a spare part that has a bottom protective film: the protective film is software and will keep the scratch permanently. The best way to get a protective film off (that does not have a protruding corner to pull) is to add such a corner with a piece of tape. Never use a knife etc. to separate this film at the lower edge where the glued flex cable contacts are: when these get separated by accident, the touchscreen is broken.
  • ​Use narrow stripes of good double-sided adhesive tape (with film) to re-glue. They are offered specifically for phone display repairs, see the tool list at the top; but you can also cut your own of course. Cutting holes in a screen-sized layer of double-sided adhesive is more secure to ward off dust, and was done by HTC originally, but seems very wasteful for a repair. Be careful to leave no gaps between the stripes, and you should be okay.
  • You can glue also at the side edges of the screen, different from how it was done originally. By folding slightly oversized the double-sided adhesive stripes at the left, right and top screen edge by 90° while pushing the screen in. You can cut off the protruding tape afterwards. This will seal the screen more tightly against dust, and should compensate for the use of narrow tape stripes instead of full-sized tape with holes for the actual screen.
  • Be careful to not let dust come between touchscreen and display. However, carefully cleaning both before putting them together, and storing them face-down, is normally sufficient. You don't need a special dust-free cabin.
  • For cleaning touchscreen and display, I wipe them with ethanol (wiping the dirt to one side), and then dry-polish the ethanol's residue with a Q-tip. This worked surprisingly well.

Software

(4) Getting your software tools ready

(5) Freeing the phone: rooting and S-OFF

See: Schritt für Schritt von S-ON zur CustomRom (step-by-step instructions, German).

 (6) Installing a Recovery solution

(7) Installing a custom ROM

(8) Installing great applications

(9) Creating backups and a backup solution

Knowledge resources

Link Collection

• HTC Desire / Incredible / Sensation family parts compatibility
• [Linksammlung] S-OFF, Rooten, Custom ROM für das Desire S (German) [TODO: integrate the links mentioned there, they normally lead to English-language pages)
• What is S-OFF?: General introduction to S-OFF, S-ON, temproot, permaroot etc.. It mentions that the "XTC Clip" device is the only way to do S-OFF, which is not true any more thanks to the software Revolutionary.

Hardware Q&A

Is it possible to exchange just the display glas while keeping the touchscreen? In theory, yes. In practice, I doubt somebody can get these two full-face glued parts apart without damaging the touchscreen, because it has a film with printed wires on the surface directly below the glas. Also, youd have to remove shattered glas from a full-area glued surface, then remove the glue and re-glue with special glue film like 3M 467 MP. As touchscreens are just 13 EUR incl. glas, this isn't worth the effort. I never tried.

How is the touchscreen built up? From the top, it consists of: glas; flex cable with contacts on the bottom side, glued to the following two layers (enabled by gaps in the following one); one layer with a circuit printed on top for the bottom edge of the touchscreen (and one wire going full round); one very thin layer with another circuit printed on top for the left and right edge of the touchscreen; one bottom layer with seemingly just the function of mechanical protection. With this buildup, the touchscreen seems to use the mutual capacitance capacitive touchscreen technology.