Service manual

Explanation for circuit operation

No. Position Kind Purpose Current Remark

1 T802 200V CRT AMP B+ 80mA

2 T802 135V HIGH VOLTAGE B+ 900mA F/B LINE

3 T802 12V GENERAL PURPOSE 600mA

4 T802 9V GENERAL PURPOSE 1000mA

5 T802 5V GENERAL PURPOSE 400mA

6 T802 5V GENERAL PURPOSE 750mA

7 T802 6.3V HEATER B+ 650mA

8 T803 +25V SUB-DY AMP B+ 900mA F/B LINE

9 T803 -25V SUB-DY AMP B+ 900mA

10 T803 30V GENERAL PURPOSE 100mA

11 T803 +7.5V GENERAL PURPOSE 100mA

12 T803 -12V GENERAL PURPOSE 300mA

13 T803 +15V AUDIO AMP B+ 2000mA

14 T803 -15V AUDIO AMP B+ 2000mA

15 T801 5V STAND-BY B+ 500mA

No. Position Kind Purpose Current Remark

<Table 1-1> The second power supply

< TABLE 1-1 > The second power supply

2-4 Explanation for power supply operation

1) Power supply and STAND-BY power

The voltage via a bipolarity power code (PC801) goes through a line filter area composed of

EMI filter (L801, L802, L827), X-capacitor (C801, C802, C803) and Y-capacitor (C804,

C805), is rectified and smoothed (C-806) in bridge diode (D801 -D804).

This voltage provides a power for STAND-BY trans (T-801) and TOP232P of STAND-BY

power IC (I801) and the second TRANS supplies a STAND-BY power for U-COM.

2) Main power start

When the U-COM supplies a PWR SWITCH ON signal for Q801 base via PA802 connector, a

positive terminal relay (RLY1) starts and AC power is rectified and smoothed (C809, C816) in

a bridge diode (D-808) via a Y-capacitor (C-811, C812).

The voltage before smoothing supplies a starting voltage for No.4 terminal of STR-F6656

(I802, I803) via (R809+R817) and (R823+R824).

When STR-F6656 starts, the voltage via a coil bead (L825, L826) goes to coil P of trans and

then to drain (Pin No.3) of internal power MOSFET of STR-F6655. The voltage flowing in coil

D supplies a power for terminal No.4 of trans STR-F6656.

Then, a current flows via R813 and R818 without going through (R809+R817) and

(R823+R824). That is, (R809+R817) and (R823+R824) supplies a current only at starting.

3) Specification of STR-F6656

The STR-F6656 is a power MOSFET and control IC built-in Fly-back type of Hybrid IC for

switching power.

The feature of this IC is a Quasi-Resonance associated operation IC that the number of parts

added to external is small, various protection functions (protection from overcurrent,

overvoltage and overheat) are offered and a power loss decreases by lowering an originating

frequency at STABD-BY.