XDA :- http://forum.xda-developers.com/forumdisplay.php?f=2115

Root 1 :- http://forum.xda-developers.com/showthread.php?t=2183942
Root 2 :- http://forum.xda-developers.com/showthread.php?t=2182792

Go to Phone then type *#*#3424#*#* to enter a HTC Function Test. ( Upon Enter Click Accept )
Make sure test everything ok only buy especially for the ones who want to buy second hand phone.

Lastly Remember warranty only accept via receipt comes together with the warranty card.
( No reciept and No Warranty Card = No Warranty )

SIS Distribution and Brightstar Corporation both have only 1 Year warranty over the HTC One.

1. Background noise or static.
Solution :- You may not be able to get rid of the problem entirely, but you can reduce it by turning off Beats Audio via the gear icon in the Notifications panel. Some people report that having NFC turned on makes it worse as well, so turn that off, too.

2. Gaps, rough edges, bulges, or scratches.
Solution :- This is really straightforward and there’s only one course of action to take. If you’re unhappy with the build quality of your HTC One, you should return it. Contact the retailer where you bought it, explain the problem, and you’ll get a replacement handset.

3. Proximity sensors not working.
Solution:- If they aren’t working then it’s a hardware fault and you’ll have to return the phone and get a replacement.

4. Unresponsive Home or Back buttons.
Solution :- If you tap lock and then unlock, or tap on the touchscreen and then try the buttons again, you might find that they are more responsive.

Go to Settings > Language & keyboard > HTC Sense input > Advanced > Calibration tool and just use a very light touch to calibrate. You should now find that the Home and Back keys are a little more responsive.

You could turn on Vibrate feedback in Settings > Sound to make sure that you are touching the button correctly.

5. Dead or stuck pixels.
Solution :- You can try an app like Dead Pixel Detect and Fix and see if it helps.

You can return the handset and get a replacement.

6. Takes a long time to charge.
Solution :- Use HTC original charger that ship together with the phone.

If charger is faulty then get a new replacement unit meanwhile use other charger to charge your HTC One.

1) Use any File Explorer in Android (Eg. ES File Explorer/ Root Explorer)
2) Locate to /proc/last_kmsg
3) Open with any text editor or copy to your computer
4) Search for "PANEL type"
5) It should show something like this "PANEL type = PANEL_ID_M7_JDI_SAMSUNG_C2_2"

For more information of panel, read from the source embeded below.
XDA Developer Source

1) Go Setting -> Language & Keyboard
2) Change System Language to "English (Singapore)"
3) Long press home button & it should work now

to redeem the free credit: register your phone via http://us.htc.com/googleplay/

Wait for 2-3 week until you get the email with the code. Proceed with either a) or b)

a) As you havent register the google wallet, here is what I did:

1) go into google play, login ur gmail or ur acc that you register under ur phone
2) click redeem at bottom middle of the page...use PC better
3) you will brought to google wallet page
4) select US country n payment method later
5) find a US postcode(any also can) and activate/register
6) connect the US VPN (http://www.getusvpn.com/ as provided by @coldfission)
7) then close the google sites
8) open the play store website again and click on redeem at the bottom of the page again
9) put in the code and volla
10) you can buy without VPN, disconnect it

b) If you have add local credit/debit card to Google Wallet before and add MY as country,

1) Change the address in Google Wallet to US address/postcode
2) connect the US VPN (http://www.getusvpn.com/ as provided by @coldfission)
3) then close the google sites
4) open the play store website again and click on redeem at the bottom of the page again
5) put in the code and volla
6) you can buy without VPN, disconnect it

*Just a reminder, users who redeemed the code won't be able to change country back after redeemed that 25 bucks, even if your Play balance is finally 0.00. Supposedly, there's some kind of "expiration date" (although unmentioned) for that Play credits, before it disappears from Wallet. But no biggie, cards should work normal-provided by EatMe

Silver :-
1. dualshock
2. Lazyboy
3. silencer5089
4. alfredtwl
5. shdin271
6. chuafc2006
7. WhitE LighteR
8. avanray
9. stephen2282
10. his
11. bayrock
12. jwrx
13. silencer
14. Eirena
15. Tr1Angel
16. edthrax
17. jb102213
18. grabulasa
19. silrave
20. rayfoo
21. chuaz
22. whistleon
23. idesmond
24. jason111785
25. uncle_toufu
26. hussain
27. eusioxn
28. sweesin82
29. cwk88
30. chriseunos
31. slashie
32. DannyOP
33. douglas_tong
34. ndom
35. cedyy
36. tenjin95
37. chester2007
38. Mukessh22
39. yayiyu99
40. vanillazai
41. adam_x
42. Bus Driver
43. AmyDazz
44. wkchard
45. Blast_Cyrus
46. sebastianX11
47. evofantasy
48. ronint
49. ccs8teen
50. kimhoong
51. jin666
52. jcksn81
53. aqemmy
54. ltw2004
55. K1d0
56. nuttyking91
57. ddevil
58. AnnaHui
59. Gigalixir
60. Seng89
61. garycheow
62. sonicbull
63. ben-w
64. DonkeyBuns
65. samsung1234
66. en_mizi
67. Enilyks34
68. dd9393
69. Vesto
70. un_id
71. FrostLance
72. PlShelpME1993
73. JulianOne
74. Satoshi3010
75. jeffreyp
76. ameer88
77. mikelim89
78. NearN
79. Witchblade
80. ppfoong
81. danes007
82. winniechen
83. cleoleeps
84. flumx91
85. 1133
86. noramin
87. ArmedandDangerous
88. lockie
89. burnst3in
90. xuldigiorgio
91. coldfission
92. lordofvirtue
93. emiwy (64gb)
94. fjive
95. davidbilly87 (64gb)
96. lengkhang
97. jacky.toh
98. gahkin
99. fighteden
100. dotn3t
101. qinshun87 (64gb)
102. Amierslims
103. Acethriller
104. bluraypirate (64gb)
105. linuss
106. deff (64gb)
107. edwfsm (64gb)
108. smokey78 (64gb)
109. jackjuan
110. tom_k3nt
111. SnapdragonS4 - dunno what color
112. lockie
113. 4eversayangu (64gb)
114. zaxxshoxx
115. Ripx2000
116. sidq
117. metalgearash1987 - dunno what color
118. dopamine
119. seanggc - China version
120. HeiShou
121. manypplwan
122. sniper on the roof - Taiwan version
123. LuffyPSP (64gb)
124. smiley.kambing (64gb)
125. GeminiGeek
126. hanny562
127. titi123 (64gb)
128. jimmy2677
129. madlocke (64gb)
130. Jason
131. zyulander
132. MikeX (64gb)
133. Choonwai11 (64gb)
134. bluetomsguy
135. EncikNazri
136. Ichi3914
137. genesyx
138. zixian96
139. CKMLY
140. ichigo89
141. ace-user
142. livinginsin
143. anthonyhee86
144. lord14383
145. cakciborEleven
146. hilmiangah
147. dreamchaser86
148. nakahee
149. alvin8866
150. tineagle
151. Scholomance
152. lyekit
153. r_p
154. bladekiller
155. Xirality
156. ameeyn
157. goldfries
158. jayro_88
159. simmy94
160. owentan328
161. vetkin_gray

Black :-
1. lunar
2. jloi
3. kingsora
4. unknowmaster
5. Agito666
6. Macrusin
7. lollygal
8. jay1220
9. Azwraith7788
10. istillmyself
11. MatShadow
12. ss1st
13. canon610
14. realmcord80
15. h11g
16. kingston5
17. Miux
18. cs_war3
19. NearN
20. chaostan
21. shreaker
22. toroy
23. ttzew
24. DCF Accessories
25. Pok Leh
26. aloy88
27. reiki_longtime
28. draex3
29. toughguy88
30. phelix
31. vincent_lms_3366
32. Aquanox28
33. i.Ken
34. darkjordan
35. jaycz8
36. mavericksam
37. solidsnake_84
38. ecitenoid
39. rhymeregim
40. anfernee10
41. nkdin_rulez
42. jeejeewong
43. hypnokey
44. devil94
45. natzakaria
46. RyoKenzaki
47. crazeed
48. ultra_nyamuk
49. miszxmaryx
50. moonsunlala
51. jamallj
52. zumapuma
53. schizo_kid
54. jepunnye (64gb)
55. snowcrash
56. Boka
57. dopamine
58. darksin_90
59. kaizor11
60. kintsuchi
61. ben5639
62. HOXVesper
63. andylow4421 (64gb)
64. mivecracers (64gb)
65. ZenXL
66. shauqimao
67. jhchong
68. boxer freak
69. Emanyshie
70. samson1618 (64gb)
71. Wan.Him
72. d2z
73. pupp82
74. DunkyKung
75. aliazx
76. amrhmzn
77. TakanoKyohei
78. epsilonphi
79. kaisertan
80. Khewzx
81. IceFlame21
82. kimjs90
83. mans

Red :-

1. catacana
2. corez
3. Macrusin
4. angkhian
5. crazee86
6. yewfatt
7. mrsyawal
8. liewdaniel
9. mansooriqbal
10. cwleong59