Topfield TF4000FI, Service Manual, Page: 13 / 62

13
5.3. The Advanced Test of Main Board.
5.3.1. Voltages on important point
- Voltage at JP4 in page 8 (of schematic diagram)
Pin
number
Minimum
voltage
Nominal
voltage
Maximum
voltage
Comment
1 +28V +30V +32V
2 +20V +22V +23V
3 +16V +17V +18V
5 +7.6V +8V +8.4V
7 not used not used not used not used
9 +3.15V +3.3V +3.4V In standby mode, it can be higher than maximum
voltage
11 +14V +15V +17V
4,6,8,
10,12
GND GND GND
* important : Be careful not to short the signals while checking the signals. It may damage the other part
of Main Board.
- Check point 1 -
Replace the SMPS. And check it again.
5.3.2. Reset
After power on by the Front Board, reset circuit works.
U8 is a voltage detector. If the voltage of 3.3V is lower than 2.7V its output goes to low.
The ‘nRESETIN’ signal should go high after power up ( when the IRD goes to Normal state from Standby
state.)
The reset signal is delayed and reconstructed in U7(TF301SC15). The reset output of U7.39 is provided to
all the system.
- Check point 1 -
In normal state, the ‘nRESETIN’ signal is about 3.3V. Check voltage at U8.1(VCC). If its value is over
2.7V, but U8.3(OUT) is about 0V, then U8 may have problem. If its voltage (U8.1) is lower than 2.7V, then
check SMPS.
- Check point 2 -
U7.39 and U7.44 should be about 3.3V. If only U7.39 is 3.3V, check the system clock.