故障现象:一台 HA868(Ⅲ)P/TSD 型电话机,不能拨号,也不能送话、受话。分析检修:首先将外线接入该电话机,拿起话筒,测量此输入端电压明显高于正常值,约为40V,说明主输入回路处于断路状态。怀疑叉簧开关的触点氧化,但经用无水酒精清洗后仍无法排除故障。仔细分析该话机电路原理图,依线路 Symptoms: A HA868 (Ⅲ) P / TSD-type phone, can not dial, you can not send and receive calls. Analysis and maintenance: First, the outside access to the phone, pick up the microphone, measuring the input voltage was significantly higher than the normal value of about 40V, indicating the main input circuit is open. Suspected hook switch contact oxidation, but still can not rule out the malfunction after cleaning with anhydrous alcohol. Carefully analyze the phone circuit diagram, according to the line