Can't Find Standbye Voltage on Toshiba Regza

[lowteq]

Hello.

I've been troubleshooting a Toshiba Regza 42XV545U over the last couple of months and I've run into some problems.

The power supply is a PE0620 V28A000841A1

When I originally received the TV it had no signs of life. I did some troubleshooting and found that a thermal fuse resister R850 was blown, I replaced it. After doing this I noticed I was getting three yellow blinking lights on the power LED, however nothing else. Some more troubleshooting and I found that fuse F820 next to the SMPS chip was blown, I replaced it and it blew again immediately. I replaced the SMPS chip Q860 and now the fuse F820 doesn't blow but I also get no signs of life at all from the TV again.

I know the power supply is at least partially alive. If I measure along the connectors going to the logic board at least some points have voltages on them. AC_DET has around 3.3V for instance, some others have 5V.

I'd like to check the standby voltage going to the main board, but I don't know what points to check, or what the voltages should be. Any assistance would be appreciated.

One thing I did notice. I measured voltage on the POWER_TV point and it sits at zero, if I press and hold the TVs power button nothing happens for a second or two, then it hopes up to 5V and back to zero again.

I've attached some screenshots of the board.

Any assistance or direction would be appreciated.

[budm]

Re: Can't Find Standbye Voltage on Toshiba Regza

We need the pictures of the whole backside of the TV showing all the boards, then we need the straight shot pictures of the whole top side and bottom of this power supply board.
POWER_TV is the same as PS-ON, so something has caused that control signal to drop out.
https://elektrotanya.com/toshiba_42x.../download.html
You will need to install TOSHIBA ZEUS ENGINE VIEWER + JAVA+ Autodesk to be able to open and view the files.

[lowteq]

Re: Can't Find Standbye Voltage on Toshiba Regza

Hello

Here are the requested screenshots.

Is it possible to bridge the gnd and one of the points in order to cause the power supply to start so I can test voltages on the other points?

Thank you.

[budm]

Re: Can't Find Standbye Voltage on Toshiba Regza

Toshiba 75013066 (PE0620C) Power Supply for 42XV545U
http://www.shopjimmy.com/toshiba-750...pply-unit.htm#

I will have to download the service manual and see what test points you will need to test.
The power supply circuits are more likely to use Active High to run on the circuit, but you must remove the wires going back to the main board first before forcing on using resistors otherwise you can damage the circuits on the main board.
BTW, did you see if the cooling fan even try to come on or not?
Pictures provided by shopjimmy

[lowteq]

Re: Can't Find Standbye Voltage on Toshiba Regza

Hello.

I will take a look at the service manual as well, I'll need to install the reader to do that.

The fan doesn't try to turn on at all.

[budm]

Re: Can't Find Standbye Voltage on Toshiba Regza

Power supply pdf.

[lowteq]

Re: Can't Find Standbye Voltage on Toshiba Regza

Hello.

It has been a few weeks since I was able to look at this. I've confirmed that my power supply board is providing the 5V standbye to the main logic board. However there is still no yellow standbye light on the front of the TV. The TV also won't start. I've tried leaving it for a few hours without luck, I also found a note that pushing the power on button for 5 seconds resets the TV, that also hasn't worked.

My suspicion is my main logic board is also dead. I'm not sure there is much I can do to troubleshoot that? Any thoughts?

[Moreno83]

Re: Can't Find Standbye Voltage on Toshiba Regza

Why is the mainboard dead? The leds were blinking in a pattern. The pattern is coming from the mainboard.

The fuses were blown on the ps so a good chance 1 or more transistors/diodes are blown. They are located on the big heatsinks.

Do you have a multimeter? If so , measure those parts for shorts.
Meter in diode mode , red and black prope on outer legs , beep is usually bad. ( Depends on circuit and if it is a transistor or diode ).

[lowteq]

Re: Can't Find Standbye Voltage on Toshiba Regza

I will check the transistors, I do do own a multimeter.

I'm under the impression that if the main logic board is getting 5V of standbye power I should be able to see the steady yellow or even diagnostic flash codes, even if the TV doesn't start.

Is that impression incorrect?

[lowteq]

Re: Can't Find Standbye Voltage on Toshiba Regza

Hello.

I took another look at the power supply in this TV and I've noticed a few oddities.

The 5V1 pin on connector P811A is providing a steady 5V, I've used the schematics that budm posted to determine that is the standbye voltage, however several of the other pins on P811A are acting strangely.

The Power_TV pin has a steady 3.18V on it
Pow_DB is usually 0V put every few seconds it jumps to 4.5V then quickly goes back to 0V.
The 12V pins start at 3.79V and over a few seconds fall to 2.2V before jumping to 3.79V again.

The fact that several of the pins have voltages which are bouncing around suggests to me that something is still very wrong with the power supply but I don't know what.

I tried to take Moreno83's advice and check the voltages on the voltage regulators but found that what I thought were voltage regulars actually aren't, they are schottky diode arrays they have part numbers of RB215T and FMW24L (D870, D871 and D872) on the schematic. I don't see any voltage regulars on this board.

I've attached some screenshots of the diode arrays and P811A again.

Does anybody have any thoughts? I'm enjoying working through this puzzle, and learning lots.

Craig.

[R_J]

Re: Can't Find Standbye Voltage on Toshiba Regza

Check the round red fuses (T*A 250V) *= amperage F871 is for +12 volts
Do you have +18 volts on pin 13 or +24 volts on pin 11 of that connector?

[lowteq]

Re: Can't Find Standbye Voltage on Toshiba Regza

Hello R_J

I checked the two fuses (F870 and F871) and they both appear to be good. They show 0 ohms when measured in both directions. I also took them out of circuit and tested like that with the same result.

Pin 13 and Pin 11 of P811A both show zero volts when the TV is plugged in but not on. I can't start the TV so I can't measure that.

One other odd thing I've noticed now. I disconnected the ribbon cable that goes from P811A to the main logic board. When I did that all of the pins except 5V1 had 0V on them. 5V1 still had 5V on it. When I plug the ribbon cable in I start seeing the voltages I described in my post from yesterday.

[R_J]

Re: Can't Find Standbye Voltage on Toshiba Regza

You say in your post "The 12V pins start at 3.79V and over a few seconds fall to 2.2V before jumping to 3.79V again."
Which 12 volt pins? pins 4,5,6, of P811A or pins 1,2 of P810A (12vlcd)?
The pin Power_tv is the ON signal from the main that turns on the pfc section of the power supply, when you remove that P811a that 3.3 volts is not there to turn on the board, If you wanted to turn on the board with that plug removed you would need about a 1K resistor placed between 5 volts standby and the power_tv pins

I wonder if C870 is ok and not open? It's not a square white cap is it?

[lowteq]

Re: Can't Find Standbye Voltage on Toshiba Regza

Hello.

Sorry for the ambiguity in my last post. The 12V pins I'm referring to are 4,5,6 of P811A.

I will check C870 tonight. It is a large blue boxy one with a rounded top. It's not the usual electrolytic can style.

Thank you for the response.

[lowteq]

Re: Can't Find Standbye Voltage on Toshiba Regza

Hello

I removed C870 and tested it.

It's capacitance is correct according the the schematic. It measured 0.70uF, the schematic said 0.068uF.

However it does appear to be open. I tried to measure it's resistance and it registered as Open Line. Normally I would expect the resistance of a capacitor to be 0 then climb up to infinity, however I've never measured a capacitor like this before. Does this mean that capacitor is bad?

I've attached a picture of it. I know it's 0.068uF and 630V, however I'm not sure what sort of capacitor it is. Does anybody know?

[budm]

Re: Can't Find Standbye Voltage on Toshiba Regza

Cap is fine.
Capacitor should show open circuit, especially the film cap. Ideal cap will have infinite resistance. Capacitor blocks DC but passes AC.

[R_J]

Re: Can't Find Standbye Voltage on Toshiba Regza

It was just a thought, those type are usually fine its those square white ones that usually go bad
So the 12 volts which is trying to come up is the supply from T860 (the ciruit you replaced the ic Q860)
It seems a bit odd that +24 does'nt come up a couple volts also as its from the same supply circuit, thats the same 24 that is used to close the SR81 relay that shorts out R850

[lowteq]

Re: Can't Find Standbye Voltage on Toshiba Regza

Hello.

I finally had time to play with this again and did some more investigating. I pulled the relay SR81 off the board and tested it. I found some weird things.

The data sheet notes two resistance values for the coil, 567 ohm at 12V or 2.3Kohm at 24V. My coil says 12V so I assume the coil resistance should be 567ohm. When I measure I only get around 270ohm (although it does fluctuate a bit around this value).

I also connected the coil side to my bench power supply and started ramping the voltage up from 0V, I could hear the relay operate at around 6V. I put my ohmmeter on the contact side and it always read infinite with the relay in either state.

The fuse resister R850 is sitting on the contact side of this relay and when I started this project that resister was blown. My assumption is the contact side of the relay was also damaged along with that resister.

I suspect I should replace this relay as well. What is the likely hood of there been other damage in the area of R850/SR81?

Any thoughts?

One other odd thing I noticed, which I think is more related to my own lack of knowledge. The relay SR81 says 12VDC on it, but the schematic notes the the input voltage to that area of the circuit is 24VDC. Is there a voltage divider somewhere that knocks the input voltage down to 12VDC?

[dick_barton]

Re: Can't Find Standbye Voltage on Toshiba Regza

If you are getting the relay to operate and the resistance is infinite at the contact side then it looks as though it's time to change the relay. The relay should say on it what the DC voltage it operates at, so apply the stated voltage to test it again.

The relay is in series with a 330 ohm resistor to the 24V line. If the relay resistance was 560 ohms then close to 15V would be applied to the relay.

[lowteq]

Re: Can't Find Standbye Voltage on Toshiba Regza

This is slightly embarrassing.

I went back and tested the relay again and got a different result. When the relay operates it does close and complete the circuit, sort of... I did some checking and a alligator clip I was using to connect to one of the leads on the relay turns out to be broken, that is why I was reading infinite resistance all the time. After fixing that problem I found that when the relay closes the contact side has a resistance of between 2 and 10 ohms, it seems to fluctuate a bit.

The resistance of the coil side is about 300 ohm lower than the spec suggests, and the resistance of the contact side when the contacts are closed is between 2 and 10 ohms. It still seems to me that this relay is bad. Do people here think that is a good assessment?

Thank you in advance
Craig.