Zenith Z50PG10 - Voltage Discrepancy 60V vs 5V ?!

[gopro25]

Hi there guys. I am a beginner hoping to become a professional.
I recently got a Z50PG10 for really cheap on craigslist.

When powered on, there is no blink or anything. The screen stays black.
If I turn up the volume, I hear static.

I have checked the voltages coming off of the main board with my plain old volt tester and everything seems fine.
Some of the voltages change constantly. I wish I had an oscilloscope.

Anyways, the only issue I can find with the voltages anywhere in the TV is on the buffer boards attached to the Y-sus board.

On both the top and bottom left side buffer boards, the circuits marked as being 5V read 60V.

I have marked in the pictures where the measurement was taken as 60V.






So this means my Y-sus board is putting out the wrong voltage, right?

So my Y-sus is bad?

Did this extra high voltage ruin my buffer boards? What about the display panel?

Am I on the right track?

Any other tips are more than welcome and very much appreciated.

After reading some other posts in this forum, I must say I am impressed with the people here. That is why I chose to come here.

Thank you in advance for your help!

-gopro25

[retiredcaps]

Re: Zenith Z50PG10 - Voltage Discrepancy 60V vs 5V ?!

Any other tips are more than welcome and very much appreciated.

After reading some other posts in this forum, I must say I am impressed with the people here. That is why I chose to come here.

If you are going to be a regular here, please follow the instructions below for uploading your pictures in the future. The people who are most likely to help you prefer NO inline images.

Composition also matters as per PlainBill

https://www.badcaps.net/forum/showpo...7&postcount=17

[gopro25]

Re: Zenith Z50PG10 - Voltage Discrepancy 60V vs 5V ?!

I would edit my post to follow your guidelines, but I don't seem to be able to find a button to edit my post....

Am I blind?

[tom66]

Re: Zenith Z50PG10 - Voltage Discrepancy 60V vs 5V ?!

The strange 5V is correct; the buffers have a floating ground of around 50 to 65V. If you measured it relative to the "-" connection near the buffers, you should measure 5V. If it were truly 60V, copious smoke would be emitted from the buffer ICs...

[gopro25]

Re: Zenith Z50PG10 - Voltage Discrepancy 60V vs 5V ?!

Okay, thank you Tom for the response.

I am confused by some of what you said though.

"floating ground of around 50 to 65V"
I looked it up, but I don't understand why it would read differently from another ground point.


"If you measured it relative to the "-" connection near the buffers, you should measure 5V."
What "-" (ground?) connection are you referring to?
All the grounds anywhere in the TV tell me 60V is coming out of the points I tested.


Lastly, If this is really not the problem, what ideas do you have for this TV?

Nothing I can see looks wrong, no blown or burnt looking parts or smells.

Every voltage I checked on each board came back fine as well.
The only discrepancy was mentioned originally.

I attached a picture, the yellow colored transformer I circled is buzzing on the main board.


When the TV is plugged in, I hear a click and a red light comes on on the front of the TV and inside on the input board.
When powered on. I hear another click, a green light shows up on the logic board, the red light on the input turns yellow, a green light shows on the input board, and the blue light on the front of the TV comes on.

The screen does not blink at all. It stays totally black.

Any ideas? Any questions? I can test voltages and Ohms.

Thank you.

[tom66]

Re: Zenith Z50PG10 - Voltage Discrepancy 60V vs 5V ?!

On one of your pictures, there is a "-" sign next to a set of holes in the board. This is your floating ground.

A ground is just a point at which voltages are measured relative to. Like a battery powered wrist watch has a ground, but it is separate from the mains circuit ground because it is not connected. Same principle but different implementation. I couldn't explain -why- they do it, though.

If you turn all the lights out with the TV on, do you see a slight glow on the screen? (It might just be in the corners for some plasma displays. And it can be really faint. Look carefully.)

If you plug in a video source with audio, do you hear the sound from the source? You might need to switch between sources using the buttons.

Once switched on, can you turn it off using the normal power button, or does the set need to be unplugged?

[gopro25]

Re: Zenith Z50PG10 - Voltage Discrepancy 60V vs 5V ?!

Looking very closely in a very dark room, no there is NO glow.

Plugged in a DVD player and YES I hear audio from it.

The set is able to switched off with the power switch both on the TV and the remote.

What now?

Oh, and thank you for your interest.

[tom66]

Re: Zenith Z50PG10 - Voltage Discrepancy 60V vs 5V ?!

Looking very closely in a very dark room, no there is NO glow.

Plugged in a DVD player and YES I hear audio from it.

The set is able to switched off with the power switch both on the TV and the remote.

What now?

Oh, and thank you for your interest.

Does the Y-sustain board have any fuses on it?

[gopro25]

Re: Zenith Z50PG10 - Voltage Discrepancy 60V vs 5V ?!

Does the Y-sustain board have any fuses on it?

Yes, just one fuse. It tests good.

[tom66]

Re: Zenith Z50PG10 - Voltage Discrepancy 60V vs 5V ?!

Yes, just one fuse. It tests good.

There is also going to be a tiny fuse for the 5V. Does this fuse test good as well?

[gopro25]

Re: Zenith Z50PG10 - Voltage Discrepancy 60V vs 5V ?!

There is also going to be a tiny fuse for the 5V. Does this fuse test good as well?

I looked all over the Y board and at the risk of sounding like a moron, I'm going to say that I don't see another fuse... How tiny are we talking? I REALLY can't find one...


Care have take a look yourself?

Sorry the picture isn't more focused....
You can see Fuse #1 in the top left corner.

Maybe this is a different looking fuse?

[PlainBill]

Re: Zenith Z50PG10 - Voltage Discrepancy 60V vs 5V ?!

LG is fond of using both 'snap in' fuses and SMT fuses on their Sustain boards. And I wouldn't be shocked if they use a pico fuse on some. Look for an object 1/4" long x 1/8" wide with gold end caps and a white body.

PlainBill

[tom66]

Re: Zenith Z50PG10 - Voltage Discrepancy 60V vs 5V ?!

It's going to be near the main fuse. Trace the 5V line from the connector.

[tom66]

Re: Zenith Z50PG10 - Voltage Discrepancy 60V vs 5V ?!

Actually, this might be a fuse.

[gopro25]

Re: Zenith Z50PG10 - Voltage Discrepancy 60V vs 5V ?!

Okay, sweet. I found 3 of the little white ones. 2 are 10 amp and one is 5 amp.

All 3 have connectivity...

Actually, this might be a fuse.

lol, good eye!

[retiredcaps]

Re: Zenith Z50PG10 - Voltage Discrepancy 60V vs 5V ?!

All 3 have connectivity...

I never suggest using continuity to check a fuse. Multimeters vary greatly in their continuity threshold. Some consider "continuous" to be 30 ohms or less. Others have a threshold as high as 1800 ohms.

So if you are relying on the beep as "continuous" and don't look at the actual reading or the multimeter doesn't report a reading, then I will argue that no fuse is good if the resistance measurement is 1700 ohms.

Instead, use ohms on the 200 scale (if manual meter). A good fuse should measure less than 1.0 ohms.

PS. This is from experience. I had a picofuse beep "good" on my Amprobe 15XP. The Amprobe has a threshold of 30 ohms +/- 10 ohms for its continuity threshold. I thought the fuse was good when in fact it was bad and measured 18 ohms.

[gopro25]

Re: Zenith Z50PG10 - Voltage Discrepancy 60V vs 5V ?!

all the fuses measured between .1 and .4 ohms....

Does this mean that the issue is not on this board?

Where else would be likely?

Any suggestions or picture requests are very very welcome.

I need to get this TV fixed...

[tom66]

Re: Zenith Z50PG10 - Voltage Discrepancy 60V vs 5V ?!

all the fuses measured between .1 and .4 ohms....

Does this mean that the issue is not on this board?

Where else would be likely?

Any suggestions or picture requests are very very welcome.

I need to get this TV fixed...

These boards are really only easy to fix with a scope. You can do basic fuse and shorting tests with a multimeter.

[gopro25]

Re: Zenith Z50PG10 - Voltage Discrepancy 60V vs 5V ?!

These boards are really only easy to fix with a scope. You can do basic fuse and shorting tests with a multimeter.

Okay. So, does anybody have a scope they would care to recommend?

[tom66]

Re: Zenith Z50PG10 - Voltage Discrepancy 60V vs 5V ?!

Okay. So, does anybody have a scope they would care to recommend?

Where are you? I picked up a good 20 MHz analog scope for £60 including one 10X probe. I use that for all my plasma TV repairs because it has a 400V rated input. (I have a second scope for bench stuff only.)