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
- The Desktop Is Dead
- Desktop SMPS Not Working
- CPU Fan Spins And Stops Repeatedly
- Diagnostic Card For Desktop Check
- Where To Buy Instrument For Desktop repair
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