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TROUBLESHOOTING
When the power switch is pressed, the Gemstar-4 assembly will attempt to turn ON the set. This is accomplished by placing a high +2.5volts on the Run/standby line to turn on the 12V regulator. Also, the Run Clock & data bus begins to communicate with other ICs within the unit. If these ICs fail to acknowledge the Gemstar-4 at turn On, the unit will shut down and try again. This will be attempted three times. Each time an error code is logged to first three parameters of the EEPROM. These error codes can be read using Chipper Check or by placing the unit into the service mode. If the unit does not pulse at power up, then follow the Dead set troubleshooting guide from the first 'POST published just before this 'Post'.
From standby, try to place the unit in service mode. If the unit will run in this state, then first check error codes. The error codes will give a clue as to which circuit is not acknowledging the Gemstar-4 at power up. In this case, VCC and Clock and Data communications can be check to each IC on the data bus.
J13103 pin 13 monitors the +12V run from U14104. At power up, this pin should read +12Volts. If the +12V supply is missing , check U14014 and associated components.
With the collector of Q14401 unsoldered, monitor J13103 pin 13 for the +12 volts at power up. If this voltage is constant, then the fault with the unit is in Horizontal section. If this is the case the troubleshoot horizontal oscillator and output side circuit. If the +12V still pulses, look for load on Run Clock and Data bus.
Disconnect J13104 to isolate the Run Clock Data Bus. With J13104 disconnected, the voltage on the Run Clock and Data bus should measure +5Volt. This will allow for a load on the Bus to be isolated.
GEMSTAR-4: NO 'OSD' TROUBLESHOOTING
J13104 pin 14 is the +5.2Volts supply for the Gemstar-4 assembly. If this supply is low, the Gemstar-4 assembly may blank out the OSD. U14103 is the 5.2Volts regulator.
J13103 pin 5 is a vertical sync pulse. This is one of two pulses used by Gemstar-4 assembly as a reference for OSD positioning . The Gemstar-4 assembly will use this vertical pulse to position the OSD vertically in the picture. The vertical output IC U14501 supplies this pulse.
J13101 pin 7 supply other pulses used by the Gemstar-4 assembly. The horizontal pulse at pin number 7 will position the OSD horizontally in the picture. A sample of flyback pulse from pin number 7 of T14401 is fed to Q13301 and Q13302, then to Gemstar-4 assembly.
J13103 pins 2,4 & 6 are the OSD outputs from the Gemstar-4 assembly. This signal is outputed from here and fed to the T-Chip, U12101, pins 34,35 & 36. The only time activity will be seen on these pins is when OSD is present.
J13103 pin 8 is the flash switch line. The purpose of the flash switch is to inform the T-Chip,U12101 where is the switch in the OSD.
GEMSTAR-4 TV GUIDE PLUS TROUBLESHOOTING.
When troubleshooting a problem where the Gemstar-4 assembly is suspected, it is important to realize that the problem is most likely not a hardware failure, but could very well be customer operation, hook up or possibly a data download problem. The first step in troubleshooting a TV Guide+ problem is to ensure the customer has the unit set up correctly.
One is the Factory Reset. This will place the module back to the original factory settings. This will clear all set up and any and all channel mapping or program listing data. If performed, a complete setup and download of both the channel map and program listing data will be necessary.
To make a factory reset is discussed in earlier posts here.
