RCA GEMSTAR-4 REPAIR HELP. DEAD SET.
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.
RCA TV - GEMSTAR-4 - REPAIR HELP - 2 NO 'OSD'
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.
