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Desktop Motherboard Power On But No Display Coming

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There can be a case when you encounter a problem like desktop motherboard power on but no display is coming.
So below we are going to see step by step[solutions for the desktop motherboard power on problem which is the most occurring problem while repairing a desktop motherboard at the chip level.

 

Step 1. Check Physically any capacitor or chip blown

Do a physical inspection to check if any capacitor or chip is blown out. Mostly a capacitor or MOSFET gets burnt out or increased in its shape. These are called faulty capacitor conditions. In that case, replace that capacitor

Step 2. Repalce RAM or CPU and Check

Secondly step is to check the motherboard by replacing RAM or CPU with another RAM or CPU of the same type. In this test, if the motherboard starts and gives output it means your CPU or RAM is faulty.

Step 3. Heat Motherboard And Recheck

In the third step heart your motherboard by a BGA machine or OVEN. After heating let the motherboard cool down. Finally check the motherboard for working. One note though, don’t check the motherboard board while it’s super hot, Let him cool down a bit.

Step 4. Check RST Light / RESET Signal Blink

The fourth step consists of checking the blink in KQCPET6 Debug Card. You should check that blink when you power on the PC. The RESET signal should blink only once.

Step 5. Check CLOCK SIgnal Glow

For the fifth step, you will check after the power button is pressed whether the CLOCK light is glowing or not in debug card. If it’s not glowing then check for a 25 MHz crystal or PCH.

Step 6. Check FRAME LED light

On debug, card check for FRAME LED light blick when you power on. If it’s not blinking then flash bios.

Flashing BIOS should solve your problem. Even if flashing BIOS on your Desktop does not give a display then replace the CPU and recheck.

If even though replacing the CPU the PC does not gives display then finally replace PCH.

Step 7. Whether Run LED Light Is Glowing

Check whether the RUN led light is glowing or not after power on the PC. If it’s not glowing then flash bios.

Flashing BIOS should solve your problem. Even if flashing BIOS your Desktop does not give display then replace CPU and recheck.

If even though replacing the CPU the PC does not give display then finally replace PCH.

Step 8. Refer Code On Debug Card

Chech for what the code is generated according to the BIOS type. Some common codes on debug cards are given below.

  1. NO         –  It means the CPU is not able to access BIOS
  2. 00 / FF  –  It means BIOS is not readable
  3. 01/ 02   –  CPU may be faulty
  4. C1 / D1 –  RAM suspected faulty

 

Desktop Motherboard Power Display Signals & Their Description

The following are Signals and their description for the desktop motherboard to turn on the PC.

Signal Description
ATX PWR OK SMPS sends a power ok signal from Gray wire saying SMPS power stable.
SYS_PWROK VRM chip generates this signal when CPU CORE VOLTAGE stable this signal going to PCH.
PFMRST PCH generates this signal called platform reset. This signal reset the entire motherboard. We can check this signal at PCI EXPRESS slot 3 Volts.
CPURST CPU gets the rest 1 Volt signal.
CPUWROK PCH sends this signal to the CPU saying CORE voltage gets stable.
DRAM_RESET CPU sends this signal to DDR and resets RAM.
CLOCK PCH generates different clock frequencies for the entire motherboard by using a 25MHz crystal.
BIOS CS & RD Pin PCH access BIOS pin no 1 chip select and pin number read pin.
FRAME Communication takes place between CPU and PCH via DMI bus that time frame signal gets generated.
RAM SM BUS Power on self test take place PCH check all devices via SM bus firstly it checks RAM SPD chip via SM BUS clock and data.
RAM CLK CPU starts communicating with RAM sending clock signals.
DMI BUS DMI bus gets active.
DISPLAY SM BUS When everything is done PCH communicates the display RGB port via SM Bus while it checks the display output is preset.
FDI BUS CPU sends graphic information to PCH via the FDI bus.
RGB OUTPUT PCH sends RGB and H sync and V sync signal to monitor.

 

 

More you can get information for basics of desktop repairing and components present with the desktop motherboard.

You can also check for dead desktop motherboards repairing for repair dead desktop motherboards with no signal even though the power button is pressed.

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CPU Fan Spins Then Stops Repeatedly

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Firstly, when we press the power button the SMPS and CPU fan spins and then stops repeatedly. This problem is due to an incomplete power rail. In the motherboard voltages turn on one after another is called a Sequence.

If one of the voltages gives some problem then the cycle is not able to complete. Then the CPU fan spins then the stops repeatedly problem occurs.

 

 

How to solve CPU fan spins then stops repeatedly

Following are steps to solve this problem of CPU fan spins then stops repeatedly :

 

Replace SMPS and recheck

The first thing to do is to change the SMPS and check with another SMPS. The problem might be SMPS.

 

Check any short circuits in the motherboard

Check for any short circuits that occurred in the motherboard. You can check it by doing hot testing and cold testing.

You will also need some tools and information about components to check this.

 

Check DDR Voltage

Thirdly do check for DDR voltage is coming or not. DIfferent DDR RAM has different DDR voltages. If it’s not coming to the check RAM Buck Converter power or if it’s coming then proceed to the next step.

 

1.05 Voltage Is Coming

Check whether a 1.05 voltage is generated or not. If it is not getting generated check for a 1.05V buck convertor. Else proceed to the next step.

 

VTT Voltage Is Ok

Firstly check whether VTT voltage is coming or not. If VTT voltage is not coming then check VTT buck convertor power, else go to the next step.

 

CPU Core Voltage Is Coming?

Check whether CPU core voltage is coming or not. If it is coming then go to the next step else check whether 12V is shorting.

If it’s not shoring then check the VR ON signal and 5V VCC supply. Secondly, If VR ON and VCC are coming then do replace the VRM chip and VRM MOSFET.

 

Check VRM PWRGD Signal Coming

If it’s coming then go to the next step.

 

Is SYS_PWROK Signal Is Going To SIO

If the SYS_PWROK signal is going then go to the next step.

 

Heat PCH And Recheck

Finally, if everything else fails heat the PCH using the SMD station and recheck. It should be working properly.

 

 

You can also check for other desktop repairing information such as a desktop motherboard repair guide, power supply for check for the dead desktop motherboard, and desktop SMPS output information.

 

 

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vinafix.com at displaymonk for Power Sequence

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The power sequence in the desktop motherboard is the exchange of signals between the motherboard Chips that takes place before anything appears on the screen.

The power sequence is the phase in which the motherboard prepares itself to function. This phase consists of sending orders to different voltages and signal generators from some ICs and receiving confirmations. Secondly, It makes sure that the principal Chips of the desktop motherboard are functional.

The Power Sequence In The Desktop Motherboard Is Given Below

The following are steps for power sequence in a desktop motherboard :

1. Standby Voltage 5VSB

Standby Voltage 5 volt sent by SMPS from its purple wire and given to SIO VSB pin.

2 Power Button Press SMPS Turn On

When the power button is pressed then communication takes place between SIO and PCH and then SPMS tuns on. After it, all buck converters turn on one after another.

3. Power Good

Firstly Power Good is a confirmation signal given to PCH.

4. Reset

The reset signal clears any junk value that remains in the chips and all chips resume.

5. Clock

Clock chips provide different clock frequencies (timing) accordingly requirements of the chips.

6. BIOS

CPU read BIOS and run stat up sequence.

7. Post

In this step, BIOS checks power on self test.

8. DIsplay

When the motherboard completes all tests display appears.

The Signal Ladder For The Power Sequence In The Desktop Motherboard

The following are steps for the signal ladder for the power sequence in the desktop motherboard :

Step No Power And Signal Steps Description For Step
1 Stand Voltage 5VSB 5 Volt standby coming from SMPS going to SIO power on. Moreover, It is VSB pin before power on.
2 Power Button Press SMPS Turn On First up all voltages get Turn On. Secondly, power gets supplied to DDR, ICH, MCH, PCH, and CPU core voltages.
3 Power Good Confirmation signal from SMPS and VRM section saying all power ok.
4 Reset All power ok signals get generated after a successful Reset signal. Secondly, PCH generates a reset called FIRST. Lastly, This signal Clear’s motherboards all existed junk values.
5 Clock In this step, the Clock Chip or PCH generates different clock frequencies according to the requirement.
6 BIOS CPU reads BIOS
7 POST Power on self test does checkings for all chips.
8 Display In this step, the motherboard displays output on the screen.

The Signal Names And Description For The Power Sequence In The Desktop Motherboards

The following are signal names and descriptions for the power sequence in the desktop motherboards repair :

Signal Name Direction Description
VSB The purple wire from SMPS Standby voltage purple wire from the power supply.
RSMRST SIO to ICH (PCH) Resume and reset signal from SIO to ICH (PCH).
PSIN(PANSW) Power witch to SIO Power switch
PSOUT(PWRON) SIO to ICH (PCH) SIO asking permission to ICH (PCH) for power on.
SLP3(SUSB) ICH (PCH) to SIO Turn on power
SLP4(SUSC) ICH(PCH) to SIO Turn on power
PSON SIO to SMPS Turn on SMPS green wire 5 volt to zero volt
PLTRST ICH(PCH) Reset the entire motherboard platform reset
CLK_EN ICH to clock chip Clock enable
CPURST MCH to CPU Reset CPU 1 volt
CLK clock Clock signal
CPU_PWRGD ICH(PCH) to CPU CPU voltage ok
PWR OK SMPS to SIO Grey wire from SMPS
VCCORE VRM to CPU CPU core voltage
GFXCORE VRM to CPU(gfx) GRAPHICS supply ok
DRAMPWRGD PCH to CPU RAM power ok
CS PCH to BIOS Chip select signal PCH ready to read BIOS
VTT POWER To CPU Internal CPU voltages
VTT_POWERGD VTT power to CPU VTT power good or it means the VTT power section is in ‘ok’ condition.

When there is no display generated then you have to check all voltages including the CPU core.
Secondly, after the PLTRST signal is generated by ICH. Finally, CPU gets reset and the CPU access’s FSB bus.

The Power Sequence for New Generations Desktop Motherboards

The following are power sequences for new generations of desktop motherboards :

Number Signal Name Description
1 5VSB and 3VDUAL 5 volt coming from purple wire SMPS. This supply is then given to SIO.
2 DPWROK Power confirmation to PCH
3 RSMRST Resume and reset are then sent by SIO to PCH.
4 SIO to ICH (PCH) Power switch signal
5 PWRON In this power switch signal is sent by SIO to PCH
6 SLP_S4, SLP_S3 Wake up the signal sent by PCH to SIO
7 PSON Power on the signal sent by SIO to SMPS
8 H/W MONITOR SIO monitor signals
9 PWROK Power ok signal from SMPS to SIO
10 DDR_EN RAM power enables signal from SIO
11 VCC1_05_EN Enable signal from SIO
12 VCC18_EN Enable signal from SIO
13 VCC1_05_PCH 1.05 volt output
14 VTT_PWRGD VTT power good signal
15 VCORE CPU CORE voltage
16 VR_RDY CPU Core voltage ready signal
17 PWROK1 Power ok signal from SIO to PCH
18 PCH_VRMPWRGD CPU power ok signal
19 PFMRST When all power ok the PCH generates this signal called platform reset.
19 CPURST SIO generates CPU reset when it receives PFMRST

You can also see for laptop chip level repair career guide to kickstart your career.

Difference Between Intel Core i3 i5 and i7 Processors

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The difference between i3, i5, and i7 is depending on various factors such as cores, caches, and threading. Firstly, we will go for checking for the main difference factors between Intel core i3 i5 and i7 Processors:

Cores Number

The more core there are in the CPU the more task can be served at the same time. This task is also known as Thread.

Turbo Boost

In Short, The Intel Turbo Boost Technology allows a processor to dynamically increase its clock speed whenever the need arises.

Cache size

Whenever the CPU finds that it keeps on using the same data over and over, it stores that data in the cache. The cache is just like RAM, only faster – because it’s built into the CPU itself. You can know more about the components of the CPU and the Identification of the CPU and its sockets.

Hyperthreading

Intel has introduced a technology called Hyper-Threading. This enables a single core to serve multiple threads.

 

What are the Changes In CPU By Intel Generation Wise

As generations of intel CPU chips grows there are absolute changes that have been made by the company. Below are changed by the company as the CPU upgraded :

  1. Introduced Nano Technology
  2. CPU core power also increased
  3. Number of cores increases
  4. Integration of graphics chip
  5. Integration of controller chip
  6. Cache memory increases
  7. Clock speed increases

 

What is the difference between Intel Core i3 i5 and i7 processors

i3 i5 i7
Cores 2 4 4
Threads 2 4 8
Turbo No 3.8ghz 4ghx
L3 cache 3MB 4MB 8MB

 

 

Difference between different generations of processors

Intel CPU Generations are code names for Intel CPU. They are given below.

 

Code Name Process Features Generations
Westmere (2010) 32nm 1st Generation CPU which is 20% faster than core 2 duo. Secondly, the memory controller is integrated into the CPU. 1st Generation
Sandy Bridge (2011) 32nm Integrated graphics and increased cache memory. Secondly, it is 10% faster than the 1st generation. 2nd Generation
Ivy Bridge (2012) 22nm Firstly, the basic difference is the DIE shrunk in size compared to Sandy Bridge. Moreover, it male improvement in graphics capability, and is targeted toward mobile applications. 3rd Generation
Haswell (2013) 22nm It has integrated PCH and a graphic chip. 4th Generation
Broadwell (2014) 14nm Firstly the basic difference is the DIE shrunk in size compared to Haswell to 14nm, which made an improvement in Thermal Design Power [TDP] 5th Generation
Skylake (2015) 14 nm This redesign gave better CPU and GPU performance. Secondly, It reduces power consumption. 6th Generation
Kaby Lake (2015) 14 nm Firstly, Kaby Lake is built on an improved 14nm process. Secondly, Kaby Lake features faster CPU clock speeds. Thirdly, the Clock speed get changes. Fourthly, Kaby Lake gets a higher Turbo frequency. Lastly, Kaby Lake is the first core architecture to support hyperthreading for the Pentium-branded desktop CPU SKU. 7th Generation
Coffee Lake 14 nm Coffee Lake has increased the core count. 8th Generation
Ice Lake 10 nm Ice Lake is firstly built on the Sunny Cove microarchitecture. Secondly, It has other features like :

  1. a 50% increase in the size of the L1 data cache,
  2. larger L2 cache,
  3. more microOP cache,
  4. increased 2nd level Thermal Design Power.
  5. Increased core width,
  6. Increment in execution ports (8 to 10),
  7. L1 store bandwidth doubled.
 9th Generation
Comet Lake 10 nm Firstly, it consists of 10th Generation Intel Core processors. They deliver the following features:

  1. improved productivity and stunning entertainment,
  2. Including up to 5.3GHz,
  3. Intel Wiki 6,
  4. Thunderbolt 3 technology,
  5. 4K HDR,
  6. Intelligent System optimization.
 10th Generation

 

You can also look for a laptop chip level repairing guide or desktop chip level repairing guide.

 

 

 

 

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How To Repair A Dead Desktop

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In this section, we will get to have a guide for repair a dead desktop. how to repair a dead desktop? is one of the most asked questions asked by newcomers in the laptop/desktop repair industry.

There are different steps we can check for a guide to repair a dead desktop.

Step 1. Check #VSB Supply Coming On SIO for repairing motherboard

Firstly check whether the 3 VSB supply is getting reached to SIO. If it is not coming then check whether 5volt coming from SMPS purple wire. If not then check SMPS, or there is a possibility is that the 3volt regulator is bad.

Step 2. Check whether the RSMRST signal is coming on SIO for the dead motherboard

Secondly, if the 3VSB supply is coming on SIO Pin then check whether the RSMRST signal is coming on SIO. If it’s not coming then there is SIO of your computer is bad.

Step 3. RTC Clock On PCH on a desktop motherboard

In the third step for dead desktop repair checking and repair check for RTC clock signal is coming on SIO. If it is not coming then replace and check the 32.7khz crystal. IF even if the RTC clock signal is not coming then Replace PCH.

Step 4. Check RTCRST SIgnal

Check there the RTCRST signal is coming as the RTCRST signal is very important in desktop repairing check. RSMRST stands for ResumeReset Signal.

Step 5. SLP_S3 (SUSB) is coming on SIO

SLP_S3 stands for Sleep S3 signal. It is important to signal for the desktop to work. Check where it is coming from on the SIO pin. If it is not coming check the DPWROK signal to PCH. Then, If it is coming then replace PCH. Finally, If it’s not coming then replace SIO.

Step 6. PSON Signal Going To SMPS on a desktop motherboard

Even if the SLP_S3 signal is coming properly and the desktop is not starting then check for the PSON signal. Check whether the PSON signal is going to SMPS. If it is not going to SPMS replace SIO.

Step 7. Replace SMPS

Finally, if nothing works from the previous steps then replace SMPS. This is the final step of repairing a dead desktop repairing.

Learning Further For Chip Level Repairing

There is a basic guide for desktop repairing guide and some schematics diagrams available which you can use to trace the current flow.

Also, you can do repairing for laptop motherboard for basic repair and advance /chip level repair.

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Desktop Motherboard Repair

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This section describes a desktop motherboard repair help guide. There are three main components responsible to turn on the motherboard. In the chip level repair guide for desktops, there are given signal names within the motherboard, also their flow is given in the below steps. All these signals flow come one after another in desktop motherboard repairing. All these signals you can check on SIO pins. So we will see these signals and their descriptions in this desktop chip level repair help guide.

Step 1. 5VSB Signal

Standby 5 volt coming from SMPS on purple wire.

Step 2. 3VSB Signal & VCCDSW3 Signal

3 volt going to Super I/O (SIO) on its VSB pin and PCH VCCDSW3_3.

Step 3. DPWROK Signal

Super I/O (SIO) sends this signal to PCH 3 volt signal.

STEP 4. SLP_SUS Signal

PCH responds after sending this signal and acknowledges the power when received.

Step 5. RSMRST Signal

Resume and reset signal to PCH which is sent by SIO.

Step 6. SLP_S3(SUSB) Signal

PCH sends this signal to SIO resuming power.

Step 7. PANSW Signal

It is a power switch signal in SMPS. It is very important for a signal for SMPS to start.

Step 8. PWRON Signal

Power button informing PCH that power button has been pressed.

Step 9. PSON Signal

Finally, this signal sends zero volts to SMPS to start.

Steps To Check CPU Core Section Working For Desktop Motherboards

The steps are also known as a flow chart. These steps are given below.

CPU Core Voltage Not Coming

Firstly check for the CPU core voltage is coming or not. This voltage consists of a 1volt load and approx 30-ampere current. You can check it on capacitors nearby.

Check VR ON Signal Coming

VR ON signal comes on VRM CHIP. Check whether that VR ON signal is coming or not.

Check NTC Signal And CPU Sense Signal Normal

NTC is a Crystal. It is situated near the CPU. It also sends an NTC signal to the VRM chip. Check whether that reading coming via a Multimeter.

Check VCC 5 Volt and 12 Volt On VRM MOSFET

A MOSFET should be tracked for 5 Volt VCC and 12 volts for properly working. you can use a multimeter to check that.

Check Any MOSFET or Capacitor Is Short Or Open

Check whether any MOSFET Or Capacitor is short or open on the line of CPU power supply line. which means MOSFET or Capacitors are not in workable condition.

Replace VRM Chip  And Recheck CPU Core Voltage

VRM chip is nearest to the SMPS power supply. Check for voltage like VTT_PWRGD 3volt, VCC 5 volt are coming and producing PCH PWRDGD and a Hot Signal. If it’s not producing the signals then firstly replace the CPU and order new chips.  Then check after fitting that new chip whether CPU core voltage is coming or not.

Replace CPU and Recheck

Lastly, if everything fails replace a CPU and check whether all things are working. You can replace it with other second-hand CPUs in stock.

VRM Chip Pinouts For CPU Core Section Working For Desktop Motherboards

Below is the pin’s description of which power signal does what on the VRM chip in a desktop motherboard.

Signals Description
VDD Supply pin 5 volt
VCCP Supply pin 5 volt
VR_ON Enable signal to the chip
PGOOD VRM chip generates this signal when core voltage is ok
LGATE1 Lower MOSFET gate 1
LGATE2 Lowe MOSFET date 2
LGATE1G
ISEN CPU Current sensing pin
NTC Thermistor measures temperature.
VR HOT When the VRM section is hot the timing chip sends out this signal
SVID Voltage identification signal which CPU communicates with VRM chip.

Troubleshooting

Below is a troubleshooting guide for desktop chip level repair

  1. The Desktop Is Dead
  2. Desktop SMPS Not Working
  3. CPU Fan Spins And Stops Repeatedly
  4. Diagnostic Card For Desktop Check
  5. Where To Buy Instrument For Desktop repair

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