What is TX RX? tx rx is type of connection which will help to you to connect your phone with pc for software operation. its just a type of connection name. what is cpu? Central processing unit. A parts of phone. its type a head of phone. all phone have cpu but for china phone cpu is very important. china phone have various type of cpu. why cpu is important for china phone? all phone have cpu, uem. but for china phone cpu is very important because various china phone cpu support various tool/device when it do software operation in phone. so though not know which phone have which cpu face problem when you repair it. How to know cpu type/model? now many of device auto detect cpu type so no problem to know which cpu use in this phone which you want to repair. also you can open the phone and can see what cpu use in phone. MTK Spreadtrum Infineon Sky/Skyworks ADI/AD Philips Agree TI / Power Management VIA SAMSUNG also come new CPU name is SI4904 what is flash chip and RAM? flash chip store phone software in it. and RAM is extra built in memory which give space to phone and flash chip to extract phone software and operating in his memory when phone is open/running. 99% china phone flash chip and RAM include in one chip. so though your flash area or ram area is damage in flash chip, you must need to change total chip. useing many type of companies chip with under various model name, as like Samsung, Toshiba, Intel, ST etc Flash chip name/model is important for china phone as like cpu? must. its important as like cpu because when flash china phone though we not know what flash chip use on it, we can find perfect flash file for it. otherwise with wrong chip flash file phone is going dead. what problem with china phone model name? model name is not a big matter for china phone. because with same name have many many phone with deference pcb, pcb design, cpu, flash chip, gate up, software etc. What need to know about a china phone when we repair? 1. CPU Type 2. Flash Chip model 3. Original software/flash file version. 4. Connector Type 5. How pin have in connector. Flash file version is important for china phone? Must. its very very important for china phone because though you lost your original (when manufacture company published phone) flash version or not know which file have in it first time, you got problem when you flash your phone. for flashing with wrong version/model flash file you got this type of problem- 1. Flash done but phone dead 2. white screen (no incoming/out going call) 3. white screen (with incomeing/outgoing call) 4. Keypad not work 5. Sim not valid 6. Sim blocked 7. Phone hang after power on 8. no network 9. have network but show emergency (this problem also do for power ic or bad connect sim or sim connector problem) 10. phone restart continuously. etc. Which tool or device? many of free tool published in market for mtk, infineon, ad, spreadtrum, sky etc. but alwayes device give you a complete solution.