CIRCUIT TRACING Component reference numbers are printed on top and bottom of the plug-in circuit board to facilitate circuit tracing. In addition, terminal numbers are also shown and referenced on the chassis schematic diagram in this manual. Transistor elements are identified as follows: E - emitter, B - base, and C - collector. COMPONENT REMOVAL Removing components from the etched board is facilitated by the fact that the circuitry (plating) appears on one side of the board only. It is recommended that a solder extracting gun be used to aid in component removal. An iron with a temperature controlled heating element would be desirable since it would reduce the possibility of damaging the board due to over-heating. The nozzle of the soldering gun is inserted directly over the component lead and when sufficiently heated, the solder is drawn away leaving the lead free from the cop- per plating. This method is particularly suitable in remov- ing multi-terminal components. CRT REPLACEMENT Use extreme care in handling the CRT, as rough handling may cause it to implode due to atmospheric pressure. Do not nick or scratch glass or subject it to any undue pressure in removal or installation. Use goggles and heavy gloves for protection. 1. Discharge CRT by shorting 2nd anode to ground through a 10k Ohm resistor. Remove CRT socket, yoke and 2nd anode lead. 2. Remove CRT from chassis by removing four screws at corners. POWER TRANSISTOR REPLACEMENT When replacing any "Plug-in" transistor, please observe the following precautions: 1. The transistor sockets are not "captive", that is, the transistor mounting screws also secure the socket. When installing the transistor, the socket must be held in its proper location. This location is indicated by flanges on the socket which fit into the heat sink. 2. When replacing the output transistors, silicone grease should be applied evenly to both sides of the mica insulator 3. All transistor mounting screws must be tight before applying power to the display. This insures proper cooling and electrical connections. NOTE: Use caution when tightening transistor mounting screws. (Torque 7 to 10 inch Ibs.) If the screw threads are qtripped by excessive pressure, a poor electrical and mechanical connection will result. |
INDIVIDUAL CIRCUIT ANALYSIS DC voltage measurements, using a meter with a 1 megohm or higher input, is useful in analyzing circuit faults in the H.V. Power Supply and Deflection Amplifier sections. Scope waveforms are useful when checking the deflec- tion amplifier and oscillator circuit. Waveforms can be compared to the scope photos in the service manual. (Refer to page 18) An ohm meter may be used to check for a shorted transistor or diode. In some cases, this can be done without removing the component from the circuit. When using an ohm meter, the AC power must be remov- ed from the display. DEFLECTION AMPLIFIER This board is held in place by mounting screws and a re- taining bracket. There are three spacers and four moun- ting grommets underneath the board to keep board away from shorting it out with side panel. There is sufficient slack in the harness so that service may be performed with the set operating and this board removed from its mounting position. All of the plugs are keyed so improper termination would be difficult. P6OO and P700 are inter- changeable for trouble shooting purposes. Deflection Amplifier Board (P299) contains "X", "Y" and "Z" amplifiers, 90V spot killer, "X" and "Y" spot killers, LED driver and DC low voltage power supply. Before trouble shooting deflection amplifier board, visual inspection of board should be made to check a short cir- cuit, broken lead or component overheating on board. Also observe the following when display is on. 1. D504 LED indicator will be on during a fault in the "X or "Y" amplifier. The above condition will drive the CRT to cut off to prevent a CRT burn. Check "X", "Y" and "Z" signal inputs, before servicing deflection amplifier board. 2. An open 90V supply will drive the CRT into cut off. Check H.V. board for 90V supply, before troubleshooting Deflection Amplifier Board. Should the sense resistors R720, R62O need replacement they must be replaced only with non-inductive resistors of the same value or display performance will be degraded. Both output channels are fused. There must be replace- ment with similar fuses for continued protection of yoke and the TO-3 output devices. The linearity controls R700, X channel, and R6OO, Y chan- nel are factory set and do not normally require adjust- ment. These controls should not be used for Gain Con- trols. They are adjusted for best linearity. Before making any adjustment on linearity controls, "X" and "Y" input signals should be checked for ±10V PIP and ± 7.5 PIP respectively while H.V. should be checked for 14.5 Ky ± 500V @ zero beam current. To check operation of the brightness and contrast con- trols, turn the contrast control (R514 green) to maximum. Adjust the brightness control (R517 grey) for a medium brightness display. Avoid high brightness levels which display retrace lines and a center spot. |