Toshiba 26AV600A

[Markus1]

Hi everyone,
I would like to ask you for some help in identifying the problem with this LCD TV.
It is Toshiba, Model 26AV600A. Its Power Supply board is marked 715G3370-1.
I did try to locate the circuit diagram for the PSU but no luck, and without the schematics I am a bit blind in diagnostic.
The symptoms are:
-at powering the set the front LED shows Green
-one or two seconds later it turns to Red
-no response from the remote control or the side buttons
-voltage at the main filter cap 340V
-STBY 5V OK
-no 24V, no 12V

Power IC (designated on the board as IC950) is an 8-pin chip A6069H. I took some voltage measurements there, and they are:
-pin 1 0V
-pin2 about 6V
-pin 3 GND
-pin4 0.8V
-pin 5 around 14V but varies
-pin 6 not connected
-pin 7 and 8 340V

Attached below: picture of the Power Supply board and datasheet of the Power IC.

I would be very grateful for your guidance here.

Regards
Markus1

[budm]

Re: Toshiba 26AV600A

Please give the dc Voltage readings on that white connector (bottom right of your picture) that goes to the the main board, each pin has label on so report the reading on each pin when TV is OFF and when power switch is activated.
BTW, this power supply has PFC Voltage booster so the DC Voltage at the two legs of the main filter cap should jump up TO >360VDC when power switch is activated and it gets PS_ON signal from the Main board.

[Markus1]

Re: Toshiba 26AV600A

Thanks budm for your reply.
I took the measurements as suggested.
Please note that the set, when plugged into the wall power outlet, immediately shows green light and in 1-2 sec it turns to red and stays red. Does not respond to any commands from the remote or side buttons.

Here are the readings on 13-pin connector when the indicator light shows Red:
pin 1 (ON/OFF) 0V
pin 2 (DIM) 0V
pin 3 to 4 (12V) 0V
pin 5 to 7 (GND) 0V
pin 8 to 9 (24V) 0V
pin 10 (PS-ON) 0V
pin 11 to 12 (5V) 5.1V
pin 13 (ACD) 0V

It was practically impossible to take any readings during a very brief period of Green light, but I could notice some variation on pin 3-4 at about 1.4V, not reliable though.

Voltage on the main filter cap is 347V.

[budm]

Re: Toshiba 26AV600A

Well, the main board is not sending out any signal to turn on the power supply, so the PFC, the 12V, the 24V power supplies are not turned on.
You will need the diagram to troubleshoot the main board. You can try disconnecting the cable to the T-CON board and to the inverter board just to see if you will get any response from the main board.

[Markus1]

Re: Toshiba 26AV600A

There is no difference with the T-con and Inverter boards disconnected.
So, you say it may be a Main board problem. What can be checked there?

The Main has the following markings:
715G3388-1 and on the bar code CBPF92JLA2, 72JLA23230619.
Any chance for a schematic diagram? I did some searching on the internet but nothing yet.

Appreciate any further advice.

[budm]

Re: Toshiba 26AV600A

Main board can be real difficult to fix, especially without the diagram. You can do simple thing such as checking the voltage regulator ICs, fuses, caps, or look real close to see if you can spot burnt component, etc.

[Markus1]

Re: Toshiba 26AV600A

It appears that this particular model is kind of rare. It probably also comes in 32 and 37 inch panels. However, my searches for a Service Manual or any schematics did not resulted in anything useful. Found some limited info on models 26AV500U and 32Av615D,B but they do not seem to be from the same family.
Unless somebody from the forum can help with the documentation I will not be able to do much more but to look for the Main board replacement.

Budm, are you absolutely positive about the problem being on the Main? Sorry, I do not intend to question your knowledge here, just trying to be certain before ordering the new board.
I am also keen to learn and get a better understanding of the circuitry and the signal flow. It is rather hard without the schematics.
So, can we verify that the PSU is OK by perhaps putting STBY 5V on the PS-ON pin to see if the 12V and 24V come up alright? Will it be save?
What are the pins On/Off and ACD? Can we simulate the signals there as well?
I would love your explanation for that.

[budm]

Re: Toshiba 26AV600A

Well, if you read my basic troubleshooting guide, you will see what those signals are for and where they are generated from.
Based on what you have reported:
Here are the readings on 13-pin connector when the indicator light shows Red:
pin 1 (ON/OFF) 0V
pin 2 (DIM) 0V
pin 3 to 4 (12V) 0V
pin 5 to 7 (GND) 0V
pin 8 to 9 (24V) 0V
pin 10 (PS-ON) 0V
pin 11 to 12 (5V) 5.1V
pin 13 (ACD) 0V
You can simulate PS_ON signal using 500~1K resistor between 5VSTBY and the PS_ON pin (but you must disconnect this signal line that goes back to the main board first).

[Markus1]

Re: Toshiba 26AV600A

Thank you Bud for staying with me. I much appreciate your guidance here.
I did notice your basic troubleshooting guide, read it too and even copied to my folder, some time ago. I guess I needed to re-visit it again, and I did.
I think I understand now the signals flow a little bit better, although far from completely.
OK for On/Off, Dim and PS-On, but still I am not quite clear about the ACD (AC Detect). Why does the Main Board need to sense AC, it already gets DC 5VSTBY? And, where is the AC signal originating from on the PS board?

Anyway, I did some additional testing on the PS. With all the connectors in place I only disconnected the PS-On line between PS and the Main board. Then bridged 5V pin, via 1k resistor, to pin PS-On. On powering the set on (just by plugging into a wall outlet, without even touching the Power On button on the side) Green front line comes on for 1-2 sec and turns to Red.
During the Green period 12v pin comes to about 1.5V, 24V pin shows nothing.
During the Red period both 12V and 24V are nil.
So it is the same behavior as previously and the PS-ON simulation did not awake the 12 and 24V lines.
How do you see it.

[budm]

Re: Toshiba 26AV600A

OK, do one more voltage checking on that main filter cap (450V cap laying on its side) to see if it does goes up to > 360VDC (PFC Voltage booster kicks on) when you force on the power supply, no need to hit power switch since we're forcing it on.

[budm]

Re: Toshiba 26AV600A

BTW, can you please provide good clear pictures of the bottom side of the power supply board?

[Markus1]

Re: Toshiba 26AV600A

Thanks for your patience Bud.
Here are further tests:
-voltage reading on the main capacitor with the force on the power supply (5V via 1k resistor to PS-On pin) is 396V DC.
-the results are the same whether its forced via the resistor or when the PS-On line is connected as normal from the Main bd.

I have reported previously reading of 347V on the filter cap. Perhaps that was incorrect, not sure about it now. I am surprised by this discrepancy.

I also would like to emphasize that the behavior of the front LED (green on AC powering from the wall outlet then red after 2 sec) is always the same in both forced or non-forced operation of the power supply. The Power On button is not being activated. It does not make any difference.

Picture of the bottom side of the power supply board attached as well.

[budm]

Re: Toshiba 26AV600A

OK, the PFC Voltage is working using force-on, but the 12V/24V is still dead even though the 12V/24V boosted voltage to run, so now we can try to fix the 12V/24V section next.
Am I correct that you still do not have 12V or 24V?
I may need the pictures of the bottom side of the power supply board but they have to be taken in section so I can clearly see the traces.

[budm]

Re: Toshiba 26AV600A

Please check the fusible resistor R925 to see if it is ope, this is used for feeding the voltage to the 12V/24V SMPS section.

[Markus1]

Re: Toshiba 26AV600A

Yes, the 24V and 12V are missing.
I checked the fusible resistor R925, and all other low ohm resistors in the vicinity R955, R958, R914, R930. All appear to be close to 0 ohms when tested in-circuit.
Attached are pictures of the underside of the power supply board, in sections.
Hope it helps.

[budm]

Re: Toshiba 26AV600A

Thanks for good pictures.
https://www.badcaps.net/forum/attach...6&d=1415673799
Can you read the P/N of that SMD IC? We need to get the spec sheet to get the pinout so we can test the voltage on the pins.

[Markus1]

Re: Toshiba 26AV600A

It is IC970, part number L6599D. As per the datasheet it is High Voltage Resonant Controller, see attached.
I will have the voltage readings on the pins tomorrow.

[Markus1]

Re: Toshiba 26AV600A

Voltage measurements on IC970 (L6599D):
pin 1 (Css) 0V
pin 2 (Del) 0V
pin 3 (CF) 0.47V
pin 4 (RFmin) 0V
pin 5 (STBY) 0V
pin 6 (Isen) 0V
pin 7 (Line) 5.87V
pin 8 (DIS) 0V
pin 9 (PFC-Stop) 0.17V
pin 10 (Gnd) 0V
pin 11 (LVG) 0V
pin 12 (Vcc) 0V
pin 13 n.c
pin 14 (Out) 0.37V
pin 15 (HVG) 0.37V
pin 16 (Vboot) 0.37V
I can see that the problem could be with pin 12 Vcc at 0V.
Again, without the circuit diagram it's hard to trace that line, so I am waiting for further instructions.

[Markus1]

Re: Toshiba 26AV600A

I should add that because the IC was located on the underside of the PS board I had to perform the voltage measurements with the board on the bench. All other connectors were off and I did not use the force-on resistor.

[budm]

Re: Toshiba 26AV600A

Yes that is going to be lots of tracing on the board to locate the switched transistor that supplies the VCC to this IC, that transistor is turned on by the same PS_ON signal which turns on another switched transistor that supplies the VCC for the PFC circuits which is working.
I will really have to look at the bottom side of the board real close to draw out the circuits so it take awhile.