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例1 [机型] AST286兼容机 [故障现象]开机屏幕无显示,BIOS的ROM不自检。 [分析与检查]系统不自检,故障一般在电源、CPU、BIOS、CMOS RAM及其外围电路,按照先易后难的原则,首先检查电源插座上的±5V、±12V、Power Good信号均正常,然后检查CMOS RAM电路。该机的CMOS RAM电路为摩托罗拉公司生产的MC146818,除了贮存设备的配置、硬件的参数外,还贮存有供电状态信息。开机后测量MC146818(24)+5V电压正常,(13)接地良好,(20)CKFS、(22)PS、(18)RESET均为正常的+5V高电平,用示波器测量②OSC1时钟信号亦正常,当测量(13)(片选)引脚时,发现该引脚为高电平,而正常时应为低电平。该片选信号由
Example 1 [Model] AST286 compatible [Symptom] The boot screen is not displayed, and the BIOS ROM is not self-tested. The system is not self-test, the fault is generally in power, CPU, BIOS, CMOS RAM and its peripheral circuits, in accordance with the principle of easy first, first check the power outlet on the ± 5V, ± 12V, Power Good signal Normal, then check the CMOS RAM circuit. The machine’s CMOS RAM circuit MC146818 produced by Motorola, in addition to the storage device configuration, hardware parameters, but also stores the power supply status information. Measure the voltage of MC146818 (24) + 5V at power-on, (13) Ground well, (20) CKFS, (22) PS, (18) RESET are normal + 5V high level, , When measuring (13) (chip select) pin, found that the pin is high, but should be low when normal. The chip select signal from