The signal processor IC7015 (STV2246 or STV2248) is fully controlled by I2C for the μC IC7600, so that the most of adjustments of the set can be made by service menu.
- Enter in Service mode: There are 2 ways to enter in Service mode - By a short circuit between pin 7 of microcontroller ( IC7600 ) and ground while the set is starting up. In this case all controls (volume, contrast, brightness and saturation) are pre-adjusted to the mid position.
- When the set is in program 75, by pressing at the same time OSD key (+) on RC and MENU key on local key board during 4 seconds.
Service mode is indicated by a S symbol on the down left corner of the screen.
- Display Service Menu : When the set is in service mode it is possible to display Service Menu by OSD key (+) on RC. Using P+, P- keys of remote control the different items can be displayed, see table bellow:
- Pre setting values: When E2PROM is replaced, pre-setting values indicated on table 8.1 are stored by the μC.
- Adjust by Service Mode: When a item is selected, using V+, V- keys of remote control it can be adjusted. Items 5, 16 and 17 have fixed values = pre setting values, rest of items.- Remove service menu: There are 2 ways to remove service menu
- Saving the new settings: Using OSD (+), MENU or INSTALL keys on RC.
- Keeping the old settings: Switching the TV to stand by. Service mode continues active.
- Remove Service Mode: Switching off the TV (be careful to disconnect pin 7 of microcontroller of ground)
Power supply and focusing:
- Power supply voltage:
- Adjust brightness and contrast controls at minimum.
- Connect a DC voltmeter across C2530 (Diagram D).
- Adjust R3518 for a required voltage depending on the model and the TRC used.
- Adjust with the potentiometer placed on the line output transformer.
SIERA SG1420 TV Service mode AFC
IF Carrier frequency can be adjusted in automatic or manual way. It is recommended the automatic way. There is an adjusting symbol for AFC on the top of the service menu consisting of a double arrow (><). If only one arrow
appears (<) or (>) AFC should be readjusted to reach double arrow (><).
Automatic AFC adjustment
- Insert a 38.9MHz 106dB/μV signal in pin11 of the tuner (1001 diagram C) across the following network:
Note: For Pal I sets, frequency is 38.9MHz only if saw filter (1015 diagram A) used is J1952.
If saw filter is J1951 frequency of the inserted signal should be 39.5MHz.
- Select AFC Adjust (item 23 of Service menu) and press V+ on RC.
- Press OSD key to save adjustment.
- Enter in Service menu again and check that adjusting symbol is correct (><). If not, readjust AFC Fine (item 2 of Service menu) till symbol is (><).
Multistandard sets A second adjustment for L’ system is necessary when the set is multistandard, to do it TV should be tuned in the first half of BI (L’ channel).
- Repeat the same automatic AFC adjustment procedure, inserting a signal of 33.9MHz instead of 38.9MHz
and using AFC LP Adj. (item 24 of Service menu) and AFC Fine LP (item 4 of Service menu).
8.3.2 Manual AFC adjustment:
- Insert the frequency signal defined in
- Adjust the value of AFC coarse (item 1 of Service menu) to 00 and the item value of AFC fine (item of Service menu) to 40.
- Increase the AFC coarse value just till adjusting symbol is (><) or (<) and adjust AFC Fine to fine a value just in the middle of the range fulfilling the correct symbol (><).
Multistandard sets TV should be tuned in the first half of BI (L’ channel)
- Repeat the AFC Manual AFC adjustment procedure inserting a signal of 33.9MHz instead of 38.9MHz and using
AFC coarse LP (item 3 of Service menu) and AFC fine LP (item 4 of Service menu).
AGC Adjustment SIERA SG1420 TV Service mode
- Connect a pattern generator to the aerial input with RF signal amplitude = 1mV.
- Adjust the value of AGC start (item 6 of Service menu) so that voltage at pin 1 of the Tuner (1001) is 3.7V.
White D SIERA SG1420 TV
Manual cut-off: Item 8 of adjusting values should be 00 (see table 8.1), that means set is in automatic cut-off. However it is possible that RGB do not start (black picture), due to grid 2 is not adjusted. In this case we recommend to change to Manual cut-off ( Item 8 = 01), pre-adjust grid 2 to have a good picture and change to automatic cut-off ( Item 8 = 0) before continue adjusting (see warm-up detection circuit in 7.1.5)
- Connect a white pattern generator.
- Adjust contrast at 07 and brightness at 22.
- Adjust VG2 potentiometer ( in line transformer ) till voltage in collector of transistor 7213 is 142V in 20"/21" or 134V in 14" (measured with a DC voltmeter).
SIERA SG1420 TV Service mode White checking:
- Connect pattern generator containing grey scale
- Adjust the set to normal operation and reduce the saturation control to minimum.
- Allow the set to warm up about 10 minutes and check visually if the grey scale has correct colour.
- If not, enter to Service menu and adjust G and B gain (items 14 and 15) until a desired grey is obtained. In the case that adjusting is difficult, start again with the setting values of table 8.1 (items 9, 10, 13, 14, 15).
Geometry SIERA SG1420 TV Service mode
- Connect a circle pattern generator with the controls at nominal conditions and enter to service menu.
- Horizontal shift: Adjust to have picture centred in horizontal position by service menu item 18.
- Vertical amplitude: Adjust picture height to cover the screen by service menu item 19.
- Vertical centring: Occasionally it is possible to correct the vertical centring cutting resistors R3400 or R3401
- TXT Shift: Horizontal shift of OSD or TXT can be adjusted by item 20 of service menu.