故障现象:开机后扬声器无任何鸣响,屏幕呈黑色无任何显示,用逻辑笔检测I/O槽中的地址总线和数据总线信号均为恒定电平的错误状态。故障分析及维修:当一个CPU的总线周期开始(ALE信号有效)或一个“高低字节转换周期”开始(CONVALE信号有效)时,U77将ARDY信号置为无效的高电平状态,然后在总线周期结束时,由U87(PAL)芯片发出低电平的ENDCYC将ARDY恢复为低电平。如果ARDY的高电平在80286的“命令状态”TC开始时已经降为低电平,则CPU在本周中不插入等待 Symptom: After powering on the loudspeaker without any sound, the screen is black without any display. The logical pen detects the error status of the address bus and the data bus signal in the I / O slot at a constant level. Fault Analysis and Maintenance: When a CPU bus cycle begins (ALE signal is valid) or a “low byte conversion cycle” start (CONVALE signal is valid), U77 ARDY signal is set to an invalid high state, and then in the bus At the end of the cycle, ARC is deasserted by an ENDCYC asserted low by the U87 (PAL) chip. If ARDY high at the 80286 “Command Status” TC has dropped to the low level at the beginning, the CPU does not insert wait this week