Toshiba 52XV645U shuts off when signal is connected.

[johnboy1313]

Re: Toshiba 52XV645U shuts off when signal is connected.

I went home at lunch and checked the voltages from the PSU. When the set is powered on with no source connected...

PJ90 (First Pic)
5V1 = 5V
12V = 12V
18V_AUDIO = 24V
15_24V(printed on opposite side of connector with 18V_AUDIO) = 24V
I didn't notice POW_TV until just now. I'll measure it and report back later.

PJ91 (second Pic)
POW_PRT, POW_SIG, AC_DET, and POW_LCD all show roughly 3.0V
12VLCD = 12V

P860 (Third Pic)
24VINV = 24V

When a source is connected and the TV shuts off...
PJ90 (First Pic)
5V1 = 5V
12V = 0
18V_AUDIO = 0
15_24V(printed on opposite side of connector with 18V_AUDIO) = 0
I didn't notice POW_TV until just now. I'll measure it and report back later.

PJ91 (second Pic)
POW_PRT = 3V
POW_SIG, AC_DET, and POW_LCD all = 0V
12VLCD = 0V

P860 (Third Pic)
24VINV = 24V (It doesn't drop at all)

Like I said, I'll check on POW_TV when I get home this evening. Thanks again.

[johnboy1313]

Re: Toshiba 52XV645U shuts off when signal is connected.

Ok, it's not 15_24, it's S_24 and it still measures 24v when on and 0 when the set powers off. The pin marked POW_TV, measures 3.2V when on and when the set turns off.

[dkneyle]

Re: Toshiba 52XV645U shuts off when signal is connected.

Regarding your post about the fuse size, I don't think you can read too much into that. Fuses are usually there to deal with significant overload (even short circuits) and to prevent major catastrophe like fires. Will it magically be in-tact at 6.9 amps and go open circuit at 7.1 amps? Unlikely. The old joke is that the expensive semiconductor will go open circuit in order to protect the 5 cent fuse.
I need to spend time looking at all your figures. There's something on-board the PSU that is detecting a fail state and shutting down those 12 and 24 volt rails. Ordinarily your description would fit with a mainboard failure, but the fact that it is OK with the other PSU tends to suggest that all is OK with the mainboard. Your last post says that the POW_TV signal remains at 3.2V in the fail state so it's getting that ON signal all OK.
Have you considered recapping it all the same? Even though they look OK they can be problematic.
If you call up the MENU screen does it power down as well? I can't make the logical connection between plugging in a source and it powering down. What about if the source is connected and you try to power up. Does it remain in the power down state?
Just looked closer at your voltage measurements. That audio supply is wrong isn't it? I wouldn't expect an 18 volt rail to read 24 volts. Measure the AC ripple on that line as well. Now it makes some sort of sense. You plug in a source that has an audio signal. Current is now drawn from that supply line. Some sort of detection circuit kicks in to say that there's a problem. See if you can analyse how the 18 volts is being derived? I'm not familar with that part of a typical PSU, but I wouldn't expect it to be particularly complicated. Again, I'd be looking hard at those caps. The AC ripple should give you an idea.

[johnboy1313]

Re: Toshiba 52XV645U shuts off when signal is connected.

The AC ripple should give you an idea.

I'll have to see if I can borrow the scope from work tomorrow. I bought one at a garage sale and it turned out to be garbage.

Thanks once again.

[dkneyle]

Re: Toshiba 52XV645U shuts off when signal is connected.

It would be worthwhile to swap back the smaller PSU and measure that Audio supply rail and see if it's closer to the stated 18 volts rather than 24 volts. I'd reckon the circuitry will be basically the same in that section.

[budm]

Re: Toshiba 52XV645U shuts off when signal is connected.

OK, so if the source is not connected the "The pin marked POW_TV, measures 3.2V when on and when the set turns off." does not toggle when you hit the power button on and off?

[johnboy1313]

Re: Toshiba 52XV645U shuts off when signal is connected.

I just pulled the two "18V_AUDIO" wires out of the harness and tried to power up. I was hoping that if that was the rail pulling everything else down, that removing that rail from the equation would allow the set to stay on. No dice. It still shits down. To answer your question, if the source is connected before power on, the set never comes on.

[johnboy1313]

Re: Toshiba 52XV645U shuts off when signal is connected.

OK, so if the source is not connected the "The pin marked POW_TV, measures 3.2V when on and when the set turns off." does not toggle when you hit the power button on and off?

It's gonna take a little while before it'll power back on Bud. I'll report back as soon as I have an answer.

[johnboy1313]

Re: Toshiba 52XV645U shuts off when signal is connected.

With the set powered on without a source connected and then shut down, POW_TV drops to 0V, as does POW_SIG, AC_DET, and POW_LCD. POW_PRT stays high at 3.2V.

[dkneyle]

Re: Toshiba 52XV645U shuts off when signal is connected.

I looked at another Toshiba PSU schematic (assuming they use a similar design) and I see that the audio power rail is a very simple full wave rectifier with a filter cap. I suppose it's possible that a rail like that could float as high as 24 volts unloaded. So maybe it was a false lead after all, especially as you pulled the output and it made no difference. The schematic I looked at used a jungle chip that did lots of monitoring and detecting and switching different parts of the supply on. They can also be tempremental at times. I running out of suggestions for this mystery!

[johnboy1313]

Re: Toshiba 52XV645U shuts off when signal is connected.

Well, thank you again for your help.

[johnboy1313]

Re: Toshiba 52XV645U shuts off when signal is connected.

Just a thought, if the PSU needs POW_SIG, AC_DET, and POW_LCD to fully power on, can I check for continuity to ground when the set shuts off and try to jumper from POW_PRT if there's no signs of a short, or will it likely fry my meter if I'm checking for continuity on a powered rail?

I'm trying to think of a way to identify which part of the PSU is failing.

[tom66]

Re: Toshiba 52XV645U shuts off when signal is connected.

You won't damage your meter but it won't give a sensible result on a powered rail

[johnboy1313]

Re: Toshiba 52XV645U shuts off when signal is connected.

Thanks Tom. Do you have any other ideas? I'm only speculating, but it seems like something is going open under load. Taking the load off causes it to work again. I'm not sure how to even trace it.

[Ltank]

Re: Toshiba 52XV645U shuts off when signal is connected.

I had on do this. The problem was the main board had HDMI problems. Plugging in a HDMI signal caused some type of a ground loop withe power to the HDMI chip, causing the protection circuits to shut it down. I had to replace the main board. I did not have a schematic to board level troubleshoot.

[johnboy1313]

Re: Toshiba 52XV645U shuts off when signal is connected.

Have you read through the thread at all Ltank? My PSU is the problem.

[budm]

Re: Toshiba 52XV645U shuts off when signal is connected.

I would disconnect the POW_TV wire from the power supply connector and use 1K resistor between the POW_TV pin on the power supply board and the standby power supply pin to force on the power supply and see if the TV will stay on with source connected.

[johnboy1313]

Re: Toshiba 52XV645U shuts off when signal is connected.

Which pin is the standby pin?

[budm]

Re: Toshiba 52XV645U shuts off when signal is connected.

It looks like the 5V1 is the standby power supply, that 5V1 should be present the minute TV is plugged into an AC outlet.

[johnboy1313]

Re: Toshiba 52XV645U shuts off when signal is connected.

Both of those pins stay high when the set shuts down on its own.