TOSHIBA 46G310U 5V power only

[budm]

Re: TOSHIBA 46G310U 5V power only

sorry that was a typo it's L6571B..
I just replaced Q101 & Q102 (12N50E), The voltage on the main cap jumps to over 370V with PS ON. then falls back to 170. Still no 12 or 24V only 5V.

OK the so the PFC circuit is working but something caused it to shutdown, we need to get that 370Vdc to be there all the time when the PS-ON is applied.
So right now the fuse has blown?
The PFC may have gone into shut down due to over current draw.

[102mm]

Re: TOSHIBA 46G310U 5V power only

OK the so the PFC circuit is working but something caused it to shutdown, we need to get that 370Vdc to be there all the time when the PS-ON is applied.
So right now the fuse has blown?
The PFC may have gone into shut down due to over current draw.

The Fuse is good. Right now as it stands I have .5V at the VCC FAN6961, it goes to Q801 and I have the voltages are below.. I used the filter cap Negative for the measurements. If i let it sit for a while the VCC will go up to about 2 volts but as soon as i connect the PS ON that will jump to about 7V then drop to about .2V and the filter fap jumps to over 370 for a moment then goes back to 170V. I thought it was Q801 so i replaced that with no success.

Q801 -2N5551
1 .5
2 1.1
3 15

U3 FAN6961
1 1.1
2 0
3 0
4 0
5 0
6 0
7 0
8 .34

U1 L6571B
1 1.1
2 0
3 0
4 0
5 0
6 0
7 0
8 .171

[budm]

Re: TOSHIBA 46G310U 5V power only

Is the VCC of FAN6961 connected to the Emitter or the Collector of Q801?
Can I get good clear closed up pictures to see how the Q801 is connected to the IC?

[102mm]

Re: TOSHIBA 46G310U 5V power only

Is the VCC of FAN6961 connected to the Emitter or the Collector of Q801?
Can I get good clear closed up pictures to see how the Q801 is connected to the IC?

It's connected to the emitter. hope the pic is better..

[budm]

Re: TOSHIBA 46G310U 5V power only

So the Collector pin 3 always has that 15VDC?
That Q801 is turned on when Optoisolator IC PC902 is turned ON (PS-ON applied, LED in side of the opto is turned on) so the photo-transistor inside the opto pin 3 and 4 will be saturated causing the bias current to flow through the resistor R810 to the BASE of Q801 which turns on Q801 to pass the current to the Emitter to the PFC IC VCC pin.
So you should have 0.6~0.7VDC between the Emitter and Base of Q801 when it is working.
This is going t o be easy troubleshooting this board without the diagram.

[102mm]

Re: TOSHIBA 46G310U 5V power only

So the Collector pin 3 always has that 15VDC?

15V at the Collector at standby, at PS ON it jumps to 18

So you should have 0.6~0.7VDC between the Emitter and Base of Q801 when it is working.

1.4V at at STBY then drops to 1.3V at PS ON and fluctuates slightly. by what you said I'll assume that is part of the problem correct? i should get the same 15 volts at the Emitter at PS ON?

That Q801 is turned on when Optoisolator IC PC902 is turned ON (PS-ON applied, LED in side of the opto is turned on) so the photo-transistor inside the opto pin 3 and 4 will be saturated causing the bias current to flow through the resistor R810 to the BASE of Q801 which turns on Q801 to pass the current to the Emitter to the PFC IC VCC pin.

when i measure the Optoisolator IC PC902 I get 15V using the filter cap GND. Measuring the voltage with both leads on it i get 6.3V at STBY and 8.5 at PS ON.

[budm]

Re: TOSHIBA 46G310U 5V power only

"1.4V at at STBY then drops to 1.3V at PS ON and fluctuates slightly. by what you said I'll assume that is part of the problem correct? i should get the same 15 volts at the Emitter at PS ON?" That cannot be right to get 1.4V, Vbe junction shoudlbe between 0.6~0.7 about the same as Diode junction diode. If it works then you should have about 15vdc at the Emitter unless there is something that loaded down so much.

[102mm]

Re: TOSHIBA 46G310U 5V power only

Update...
the low side of the Optoisolator IC PC902 holds steady at 5V at STBY. At PS ON it drops to .5V





This thing is so complicated.

[budm]

Re: TOSHIBA 46G310U 5V power only

That is about right, 0.5VDC measured between pin 3 and pin 4 of that opto pc902, the Photo transistor is fully turned on to give to allow current to flow through that R810 to the BASE of Q801 which should be fully on to pass that 15V to the Emitter. You can see that connector of the BASE of that transistor.

[budm]

Re: TOSHIBA 46G310U 5V power only

I forget to ask, did you replace the two caps C11 and C802?

[102mm]

Re: TOSHIBA 46G310U 5V power only

I forget to ask, did you replace the two caps C11 and C802?

I hadn't, but i just did and no change. It sounds crazy but i just tried to short the collector and emitter of Q801. the Filter cap jumped to 398V. but The problem getting the voltage to U3, isn't it..

[budm]

Re: TOSHIBA 46G310U 5V power only

Q801 is for feeding the VCC to the PFC IC U3 and now you know the PFC circuit is OK since now you are getting the 398VDC, so you need to find out why Q801 is not turned on by the Opto, then you need to see if you need to find out how U1 the SMPS IC for the 12V/24V gets the VCC from to run.