Toshiba 50HP66 - never turns on, clicks off when relay does

[vince_o]

My apologies for a newbie post but I'll endure some flak if I learn a bit about fixing TVs--well, okay, just this one TV. Someone gave me a 2006 Toshiba 50HP66 that "didn't work". Its PSU was replaced as the only repair attempt which didn't fix it. The owner got a new TV, I took this one.

I've read various posts (here and elsewhere) and, although I can fix various things, electronics at this level is sometimes a bit beyond my skill level. So, please bear with me as I stumble through the basics to get to where you can help (if possible).

What I have - Toshiba 50HP66
What it does

red LED on front glows when A/C is applied, goes dark when relay on PSU clicks (in about 3-5 seconds). LED may go green for a brief second if I press Power before the relay clicks but, once it clicks, it's dark for good.

What I've done

Unplugged x-sus = same thing
Unplugged y-sus = same thing
Tested three fuses = all good
Tested Va, Vs - got some numbers but, because of the relay click, am not sure if I checked them right

I've attached photos of the PSU, the x-sus, the y-sus, and a closeup of B45 on the y-sus because that's the only burn mark I can see.

Thanks.

[mmartell]

Re: Toshiba 50HP66 - never turns on, clicks off when relay does

This set is essentially an LG 50PC1D I think. There should be lots of info on that so do a search for that model and see what you can dig up.

[vince_o]

Re: Toshiba 50HP66 - never turns on, clicks off when relay does

Thanks for the reply and directing me to the possible cause. If it is that simple (the AC detect pin is unstable) and it can be fixed with a bit of solder, I will be very impressed. I'll let you know what I find.

Thanks again.

[freakaftr8]

Re: Toshiba 50HP66 - never turns on, clicks off when relay does

I can verify that that power supply us made by sony and also it will not stay powered up if one or more sustain boards are disconnected. Check IPM modules on y and zsus. If o e is shorted and didn't blow a fuse on the ysus then it's deaf short putting the power supply in protect mode. Do a ohm check from vs to ground in both sustain boards. If one is shorted to ground there's your problem. These sets are so prone to IPM failures it's amazing. I've had hands on experience with this model in my earlier years when I was leaning about plasmas. Then I have pickled with almost every rebranded lg pc1d there is. Lol.

[vince_o]

Re: Toshiba 50HP66 - never turns on, clicks off when relay does

Since the PSU was acting the same (relay shutting off the power downstream) whether or not anything was plugged into it, I was thinking it was the PSU. But, like I said, I'm learning.

Taking your suggestion, I tested continuity between Vs and chassis on both y-sus and z-sus boards but it didn't act as expected. To wit, if I test continuity between chassis and:

• chassis, my DMM beeps.
• GND, my DMM beeps.
• Vs, the DMM beeps briefly and then resistance goes back to 1.
• Vs again, no continuity.

This happened on both boards so I'm not sure what is happening. If there was a short, shouldn't it stay a short (ignoring the loose or broken wire scenario)? I considered that my DMM was holding some type of charge and the short beep was the Vs discharging but that seemed too much of a wild guess.


I'll try any other suggestions but it looks as if the boards will be going to rehab next week. Still cheaper than a new TV.



Thanks again.

[mmartell]

Re: Toshiba 50HP66 - never turns on, clicks off when relay does

Not sure where you found Va and Vs, you should use the pins on the backside of the ipm modules under the board. The should be labelled. Did you check the fuses ?

[vince_o]

Re: Toshiba 50HP66 - never turns on, clicks off when relay does

Fuses were checked several times and all found good.

I found Vs on the top side where the plug either comes in (z-sus) or goes out (y-sus) on that connector. I never figured there'd be another way. To test the underside, I'd have to remove the board and that seems add complexity to what should be a simple test. Then again, testing at the source does eliminate the link between the IPM and the connector...hmm.

Not to sound ignorant (too much) but what's the downside to testing at the connector? Because I am presuming that the link between the IPM/connector is good?

[mmartell]

Re: Toshiba 50HP66 - never turns on, clicks off when relay does

The fuse is in between, which is why I was asking if it was checked. Sounds like at worst you would have only an "open" ipm (they can fail open) which shouldn't prevent the set from starting.

You could try running the auto-gen (test patterns) to remove any main board fault from the equation. Short pins 1-2 on the control board connector P1 (?) And disconnect the lvds cable going to the main board and plug it in.

[vince_o]

Re: Toshiba 50HP66 - never turns on, clicks off when relay does

Testing the fuse before assuming a result makes sense. Thanks for the clarification.

I had to decipher the second paragraph but, after I disconnected the LVDS cable, shorted pins 1-2 on P1, and applied power, the relay still trips in less than 3 seconds. Power (110V) still exists in places but DC voltage fades faster than I can find and measure it.

[mmartell]

Re: Toshiba 50HP66 - never turns on, clicks off when relay does

I would test all fets on ysus and zsus for shorts. They can short without popping the fuse.

[vince_o]

Re: Toshiba 50HP66 - never turns on, clicks off when relay does

Thanks for the suggestion. I checked everything that looked like a FET and found two on the z-sus board (D203, D204) and one on the y-sus (Q12). Although the next step is probably replacing these FETs (which I could do), it would be faster to send these boards to rehab in case there's something else to be fixed.

Thanks.

[mmartell]

Re: Toshiba 50HP66 - never turns on, clicks off when relay does

There are three fets each on the upper and lower buffer boards, make sure you check those as well. I'm about to dive back into this exact set (suspected ipm failure) so if you want to tackle any repairs just let me know if you need any measurements.

[vince_o]

Re: Toshiba 50HP66 - never turns on, clicks off when relay does

Before I continue, let me verify my FET test method. I'm familiar with electrical work (low-voltage and 110 stuff) but circuit boards are not my cup of tea.

When you said test the FETs for shorts, I put one probe of my DMM on the frame and the other on one of the three legs of the FET. If I heard a tone, that's what I considered a short. If that's not right, let me know the proper way to test a FET.

My dilemma for continuing is the repair shop says they won't touch a board if they see evidence of a previous repair attempt. So, I can spend the $$ for them to fix it but I'm sure I'd be much happier if I could do it with this board's help for a few dollars.

Being the cheapskate I am , I think I know my answer but wanted to see if you all are willing to put up with a noob's learning curve.

Thanks.

[freakaftr8]

Re: Toshiba 50HP66 - never turns on, clicks off when relay does

normally I take the black probe put it on the middle pin and then the red probe on each side of the MOSFET. when you get a beep its most likely shorted. however a lot of boards are set up with MOSFETs in series so what I do is look for the MOSFET and the bank of shorted MOSFETs to have the lowest reading on either pin and usually you will find that one is the shorted one

[mmartell]

Re: Toshiba 50HP66 - never turns on, clicks off when relay does

Freak, i think you meant parallel ? Also, vince, keep in mind a beep is not necessarily a short as your meter will beep below a certain resistance reading - maybe 100 ohms even. There are some resistors <1 ohm. If you touch your two probes together you will see what your meter registers as a dead short.

That being said any beeping while testing a mosfet would likely be a short or at least warrant further investigation. At least that is my understanding of it.

[retiredcaps]

Re: Toshiba 50HP66 - never turns on, clicks off when relay does

Also, vince, keep in mind a beep is not necessarily a short as your meter will beep below a certain resistance reading - maybe 100 ohms even.

Let me expand on the above point. I know a lot of people (probably 98%) use continuity to test for shorts. That is okay, if and only if, you know what the continuity threshold of your meter is. The same 98% will have no clue as to what this value is.

One Mastech multimeter, I know from reading the manual, considers something continuous and beeps if the resistance reading is less than 1800 ohms. If you are using this particular meter to check a fuse and hear a beep, you might be fooled into thinking the fuse is good. A good fuse should be less than 1.0 ohms.

Some multimeters consider something continuous and beeps if the resistance reading is less than 20 ohms. If you are using these meters to check for shorts and assume something is not shorted because you don't hear a beep, you can be misled as well. I would argue that a mosfet, if it read 30 ohms, between any two pins, you likely have a bad mosfet.

You should always report your actual readings and not "it tested good". That is, I got 22 ohms.

[mmartell]

Re: Toshiba 50HP66 - never turns on, clicks off when relay does

This actually fooled me for a time when I started out. Heard the beep and thought "short!" before my deductive reasoning kicked in

[vince_o]

Re: Toshiba 50HP66 - never turns on, clicks off when relay does

Thanks for the clarification on how to test for shorts. My DMM's threshold is somewhere about 200 and, you're right, I was presuming a short just because of a beep.

When I retested the FETs last night, they seemed to be consistent. Either the two legs matched (lowest was mid-300's) or one was 3-400 and the other had much higher resistance. So, I guess I don't have FETs shorting like I thought.

The PO says he has the original power supply board so I may put that back in and see if it acts the same.

Thanks.

[vince_o]

Re: Toshiba 50HP66 - never turns on, clicks off when relay does

Oh boy, I get to hijack my own thread!

Put the original PSU back in last night. Powered it up, a few seconds later, I heard a loud "pop!". Oh well, at least it's acting differently.

Unplugged it, waited a minute, tried again--it stayed on! Pressed Power, the front LED turned green--and stayed on. Three LEDs and one under the LVDS cable lit up on the CTRL board. Great! It's acting "normal". Pressed Power several more times and the TV responded properly. (Guess the PO bought a bum PSU.) On to the front.

When I turn it on, I get about a dozen vertical white/reddish bars, first on the left and then in the center. I also hear some slight buzzing from the y-sus's lower IPM (the board is loose because I removed most of the screws and the buzz goes away if I press down). I have not left it on long enough to see if any IPM has a different temperature from the others.

Since it stays on, I measured Vs (199) and Va (~62). (FYI, I backprobed the GND and Vs/Va pins to get my reading.)

Now that my problem has now changed to something I think I've read about in the forums, I'll redo my search. If I should cancel this thread or change the subject, let me know.

Thanks.

[mmartell]

Re: Toshiba 50HP66 - never turns on, clicks off when relay does

Thanks for the clarification on how to test for shorts. My DMM's threshold is somewhere about 200 and, you're right, I was presuming a short just because of a beep.

When I retested the FETs last night, they seemed to be consistent. Either the two legs matched (lowest was mid-300's) or one was 3-400 and the other had much higher resistance. So, I guess I don't have FETs shorting like I thought.

The PO says he has the original power supply board so I may put that back in and see if it acts the same.

Thanks.

Are both buffer boards testing the same ? Sounds to me like you DO have a short. Try one buffer at a time and see if you get a proper half screen picture.