High voltage shut down. The high voltage at the final anode of the piclture tube exceeds 33kv (33,000VDC), and the unit goes immediately to safety mode.
The cause for this fault is with the power supply regulator section itself. The secondary [B+] voltage exceeds (135VDC) which in turn supply to pin number 2 of line output transfomer. The main problem to this will always be to loose solder terminals at the power regulator section.
Get a close look to all solder terminals to power supply regulator STR, SMPS trasformer and assiciated components, whichever heats during working. Most of the components in this section will heat up to an extent. Repeated heating and cooling might make the solder terminals to get loose. This is a common fault to most of the Sony TVs.
The detection of loose solder terminals are somewhat difficult to detect, as they will be very samll; usually microscopic to detect with normal sight. Do this as most of the service persons do. Resolder all the suspected solder terminals, by applying a little more solder, without making any solder bridge short in between adjecent solder terminals. It will be best to suck out the solder from the terminals of STR and SMPS transformer, and resolder them with fresh solder.
In most cases, about 90%, the fault will be with these soleder terminals. Check the B+ voltage after resolder process.
To do this, make a temporary break on the B+ track, somewhere after [C630 - 33mfd 160v]. In this set, B+ voltage is connected directly to pin number 11 of line output transformer, without any current limiting resistor. So, if we switch ON the set, while the B+ supply connected to LOT, if the fault hasn't been rectified after resoldering process, the fault will emerge again.
Therefore, we have to make sure that the B+ is within the range of 137 & 133VDC. After making a print break, connect a 100W bulb [FILAMENT TYPE ONLY], across C630, switch ON the set and measure the B+ for normal voltage.
If found abnormal, make sure that there is some component fault. The main fault will be due to faulty STR. Here [STR-F6654] is used as swithing regulator. Compare the voltages of the 5 pins of this IC.
Pin 1 = OCP [back pulse from SMPS transformer]
pin 2 = 0V [Source lead of internal FET]
Pin 3 = 169.8VDC [Drain lead of internal FET]
Pin 4 = 17VDC
Pin 4 = Ground.
If any of these voltages found abnormal, no need to check further. Replace the STR.
Never connect the breaked print line, till you measure the B+ volt normal.
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