GEMSTAR-4 ASSY'S
SET CONDITION :: DEAD
J13103, pin [18] is the Run/Standby line. At Power Up, this pin should rise to (+2.5V) to run On [Q14105] in the 12V regulator circuit of [U14104]. For this to occur, the Gemstar-4 IC, U26401 VCC and Reset must be present. This also indicates U26401 has acknowledged the EEPROM, [U13102]. Activity on this pin when power is pressed indicates the Gemstar-4 assy's is attempting to turn the unit On.
When the Power is pushed, J13103 pin 18 should rise to (+2.5V). If the pin holds at +2.5Volts, but yet the unit appears to be dead, it is recommended the Horizontal circuit be checked. If pin pulses from '0' to '2.5' volts, then the unit is trying to start. First try to read the Error Codes using Chipper check. Another method is to place the set the Service Mode to read the Error Codes. Using the front panel switches, Press and Hold the Menu Button, then Push and Release Volume Up. If the set stays running, then read the Error Codes. If the set will not stay running, then try to unsolder the collector of Horizontal Output Transistor [Q14401]. Try to turn On the set. If pin 18 stays at +2.5Volts, troubleshoot the Horizontal Output Circuit. If pin 18 still pulsates, then check the Run Clock and Data lines, J13104 pins [13 & 14] for load.
J13103 pin 13 monitors the +12V run from U14104. If this 12V supply is missing, then check U14104 and associated components.
J13104 pins 7 is the +5.2V supply for the Gemstar-4 assy's. U14103 is the 5.2V regulator.
J13104 pin 7 is the reset voltage to the Gemstar ass'y. The reset circuit is located on the main board. Shortly after plug in this pin will rise to +5.2Volts. This circuit is comprised of Q13501 and Q13503.
J13104 pin 10 is the KD/ATE enable. This pin will normally measure at +1.6Volts. The Gemstar-4 IC, U26401 holds this pin low (0v) while acknowledging the EEPROM, U13102. If this pin stays low, but VCC and Reset are present indicates that U26401 cannot communicate properly with U13102. It will then be necessary to check U13102 and associated components.
J13103 pin 15 is the 16-V standby. This allows U26401 to monitor the regulator circuit. Should the voltage of this pin drop. U26401 will run the Batten Down the Hatches routine with the EEPROM to save the current settings and shut down the unit. This pin should measure +16Volts at all times.
J13103 pin number 9 is the IR input to the Gemstar-4 ass'y while J13104 pins 4,6 & 8 will be the key scan inputs from the Front Panel Switches. Under normal conditions these pins will measure +5Volts. If the DC voltage is low on any of these pins of if a scope reveals noise on the IR pin, U26401 my interrupt this as a command and will not perform another command until the pin return to normal.
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