United-Motors-Service-Delco-987575 电路原理图.pdf

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1、157 收音机爱 好者资料库 RadioFans.CN VOLUME R 17, MOST-OFTEN-NEEDED 1957 RADIO SERVICING INFORMATION UNITED MOTORS Chevrolet 987575 (Continued from page 157) TROUBLE SHOOTING THE OUTPUT STAGE A quick way to determine that the 2N173 is conducting can be made by checking the collector voltage, from tran sistor

2、 case to the radio case. If no voltage is present the transistor is not conducting or the transistor heat radiator is grounded to the radio case. If the voltage at the col lector is higher than listed the transistor is conducting too heavily (check with milliammeter) or the output trans former is op

3、en. The amount of current the transistor conducts is determined by the voltages at each element, the resistor in the base and emitter circuits, the input transformer secondary resistance, and the transistor itself. The most common defect in the transistor is an internal short between emitter and col

4、lector. To check for this, use the following procedure: 1. Unsolder base and emitter leads from the circuit. 2. Set ohmmeter on the R x 1” scale (no other scale should be used). 3 Place negative lead of ohmmeter (polarity refers to internal ohmmeter battery) on collector, and positive lead on the em

5、itter. 4. The transistor is shorted if reading is O If a transistor is replaced, the bias* adjustment should be made for the new transistor. Insert a milliammeter in the collector lead and adjust the bias control for a col lector current of 930 ma. HOD, ICO cun COLLECTOR STUD B SI O w H e I B, a PAR

6、TS LAYOUTTUBE VIEW ALIGNMENT PROCEDURE Series Capacitor or Dummy Antenna 0.000068 Mfd. 0.000068 Mfd. 0.000068 Mfd. 0.000068 Mfd. Connect Signal Generator to 12AD6 Grid (Pin #7) Antenna Connector Antenna Connector Antenna Connector Antenna Connector Signal Generator Frequency 1615 KC Tune Receiver to

7、 High Frequency Stop High Frequency Stop Signal Generator Signal High Frequency Stop Signal Generator Signal Adjust in Sequence For Max. Output A, B, C, D *E, F, G J, K F, G Before making this adjustment check mechanical setting of oscillator core H. The rear of the core should be 1%* from the mount

8、ing end of the coil form (This measurement is readily made by inserting a suitable plug in the mounting end of the coil form.) Core adjustment should be made with a non-metallic screw driver. *L is the pointer adjustment which is on the connecting link, between the pointer assembly and core guide ba

9、r. It should be adjusted so that when looking directly at the dial the pointer is on the 1100 KC mark. This setting is to give the correct relationship between the pointer and the dial when the radio is installed in a car. With the radio installed and the car antenna plugged in adjust the antenna trimmer G for maximum volume with the radio tuned to a weak station between 600 and 1000 KC (see sticker on case.) 158 收音机爱 好者资料库 RadioFans.CN