How to repair the reset circuit?
No reset fault is a common phenomenon in mainboard maintenance.
Many maintenance personnel only measure the complex signal of PCT interpolation, no reset and no reset of CPU.
1. There is no reset on the whole board.
The non-reset fault phenomenon of the whole board is that the PCI slot reset signal measurement point voltage is 0 V, the maintenance methods are as follows.
1)Check that the reset switch is high. Replacement of connected components from the reset switch tap line at a voltage of 0 V.
2) Check the main board of memory power supply, bridge power supply, bus power supply CPU power, South Bridge chip the second standby voltage is normal. Repair the power supply circuit according to the maintenance method. AMD chipset should check the CMOS battery power supply.
3) Check whether the clock signal measurement point voltage is normal, or measure the clock chip peripheral resistance voltage 1.6 V and 0.4 V (nVIDIA, AMD,Intel single bridge can skip this step). The clock signal is wrong, check the working conditions of the clock chip or replace the clock chip according to the maintenance method of the clock circuit.
4)Check the bridge PWROK (Intel chipset called PWROK, AMD chipset called PWR_GOOD, nVIDIA chipset called HT VLD) is high level 33V if there is no voltage, according to the principle of PWROK signal generation of each chip, check the generating conditions and conversion circuit.
5) The Intel chipset motherboard also needs to check if the VRMPWRGD of the South Bridge chip is high.
6) Bridge power supply, clock signals, PWROK signals are normal after replacing the South Bridge chip.
2. CPU had no reset.
CPU non-reset means that the reset signal voltage of the CPU is lower than the normal value.
The normal values of reset voltage of Intel 478, Intel 775, Intel13, 15, IV, AMD 754,939 and AMD AM2 are 1.2 V, 1.2 V, 1.5 × 2.5 V and 1.8 V respectively, and the normal value of reset voltage of AMD AM2 is 1.2 V, the normal value of reset voltage of AMD AM2 15 is 1.2V, the normal value of reset voltage of AMD AM2 is 1.2V, the normal value of reset voltage of AMD AM2 is 1.2V. The normal reset voltage of the AMD AM3 is 1.5V.
The CPU reset signal of the main board of the nVIDIA,AMD chip is sent directly by the South Bridge chip. When there is no CPU reset signal, the working conditions of the South Bridge chip are checked according to the maintenance method of the non PCI reset signal. Only the Intel dual bridge motherboard is the North Bridge Chip reset CPU.. In this paper, Intel dual-bridge motherboard, CPU reset-free maintenance methods are as follows.
1)Check the working voltage of the North Bridge chip (memory power supply / video card power supply bus power supply and other power supply small inductors).
2)Check the clock signal of the North Bridge chip.
3)Check the PWROK of the North Bridge chip (generally the same route as the PWROK of the South Bridge chip, since the PCI reset signal is normal, can be ignored.)
4)Check that the North Bridge chip receives a normal PLIRST# (check that all onboard chips and slots have reset signals).
5) Use false load to hit the CPURST# point value to prevent CPU sockets from being welded empty.
6)The above inspection is not a problem, finally replace the North Bridge chip. Note: there is a problem with the line between the North and South Bridge chips of the Intel chipset, and the failure of the South Bridge Chip will lead to no CPURST#.
This article is from Allicdata Electronics Limited. Reprinted need to indicate the source.