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

[gopro25]

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

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.)

I'm in Tucson, az, US

...

Just so I have something to try to work out before I get the scope, which boards, would you say, are the most likely culprits, in order, to be causing the lack of screen display?

Thanks very much for your help so far.

[tom66]

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

Y-sustain followed by Z-sustain followed by power supply followed by everything else.

[gopro25]

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

Until I get the scope, is there any way that I can narrow down the options with just my multimeter?

[tom66]

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

Until I get the scope, is there any way that I can narrow down the options with just my multimeter?

Check the voltage between these pins, should be close to 5V.

[gopro25]

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

Check the voltage between these pins, should be close to 5V.

Yup. It varies slowly between 4.98 and 5.01 according to my tester.


Also, here are some admittedly bad pictures of the Z-sustain and main boards.
If clearer images are needed, I can try tomorrow in the sunlight.

I circled the two fuses I found on each board. All tested good.



On the main board, the wires that lead to the Y-sustain and Z-sustain tested as follows while unplugged:
Vs:193.6V
N. C: Goes from 0-197V increasing at a rate about 20-30V per second
Va: 59.6V
M5v: 5.06V

On the main board, the wires that lead to the input board tested as follows:
16v: 16.41V
12v: 12.07V
5v: 5.09V
AC_DET: 5.07V
5V_DET: 5.07V
VS_ON: 3.27V
RL_ON: 4.57V
AUTO: 0
M5V_ON 3.27V

On the Z-sustain board, I don't see much to measure.
I did see a little green resistor marked VZb+.
That measured 98.3V.

[gopro25]

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

Also before you mention it, I found the 3rd fuse on the Z-sustain board. It's good too.

[tom66]

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

Okay, so it looks like the supply voltages are okay. Do you hear any buzzing from either sustain board? Unplug one to confirm. It will be faint, high pitched whining, if the board is working.

[rpgruss]

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

You can also touch the heatsinks on the y and z sustain boards. They will be warm if the board is working.

[tom66]

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

You can also touch the heatsinks on the y and z sustain boards. They will be warm if the board is working.

I would avoid this while it is running - you cannot be sure if the heatsinks are connected to any part of the sustain board electrically. If it's off (unplugged), that's fine.

[gopro25]

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

Upon powering on Y-sustain starts off sounding like a very quiet scanner for half a second then goes to the high pitched ringing seemingly coming from the yellow transformer.

Z-sustain groans. Deep, Higher, Deep, Distorted.

Does this mean Z sustain is the problem?

[tom66]

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

Upon powering on Y-sustain starts off sounding like a very quiet scanner for half a second then goes to the high pitched ringing.

Z-sustain groans. Deep, Higher, Deep, Distorted.

That suggests a faulty Z-sustain. Is that with Y-sustain unplugged?

[gopro25]

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

That suggests a faulty Z-sustain. Is that with Y-sustain unplugged?

Ah, right.
With Y-sustain unplugged, the Z-sustain growling falls silent.

[tom66]

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

Ah, right.
With Y-sustain unplugged, the Z-sustain growling falls silent.

That suggests that the boards are synchronised in some way, I suspect the Z-sustain to be failed, but they usually go silent when faulty.

If you unplug the Z-sustain you should get a very faint, but visible image. It might only be visible in the corner of the screen, and it will likely be very motion blurred.

Also, check any diodes and MOSFETs that are visible on the board, if you can. You can use your multimeter's diode check. Check all combinations of pins. Diodes should conduct one way (dropping 200 - 800mV) and not the other. MOSFETs should appear completely open circuit.

[gopro25]

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

That suggests that the boards are synchronised in some way, I suspect the Z-sustain to be failed, but they usually go silent when faulty.

If you unplug the Z-sustain you should get a very faint, but visible image. It might only be visible in the corner of the screen, and it will likely be very motion blurred.

Also, check any diodes and MOSFETs that are visible on the board, if you can. You can use your multimeter's diode check. Check all combinations of pins. Diodes should conduct one way (dropping 200 - 800mV) and not the other. MOSFETs should appear completely open circuit.

I am confused.
I unplug the Z-sustain board, but I get no image change on the screen. It remains unlit and without picture.

Also, I just noticed, the main power board makes a deeper humming sound too.

I am confused testing the MOSFETS...

This page gives relatively clear instructions...
http://www.sentex.ca/~mec1995/gadgets/mostest.htm

It also says that I need to have a multimeter with a diode test voltage of 3.3V or more... Looked mine up, it's 1.5.

Does this mean I can't test?

Each one seems to do something different.
Between source and gate on the ones I see:
.551
.613
.000
.830 big one
.830 big one
.559 big one
.559 big one
.000

When I switch the positive to the drain pin I get no connection sometimes and other times wonky numbers again.

Also, I don't see anything that looks like a diode.



help...

[gopro25]

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

bump

[tom66]

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

Sorry, I missed your post - if you're getting zero between source and gate that signifies a problem with the MOSFET. Check between source and drain too.

[LeeElectrode]

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

Hi,
My name is Lee and I'm new to this forum. I picked up a Z50PG10 free off of Craigslist and thought I would give the repair a shot. I've been in electronics and computers all my life so I'm pretty at home around components. I have a scope an am ready to dive into this beauty. This thread seems to have just dropped off and I'm wondering if Tom66 ever got the unit fixed and what was the solution. Anyone have any news?

Lee

[tom66]

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

Hi,
My name is Lee and I'm new to this forum. I picked up a Z50PG10 free off of Craigslist and thought I would give the repair a shot. I've been in electronics and computers all my life so I'm pretty at home around components. I have a scope an am ready to dive into this beauty. This thread seems to have just dropped off and I'm wondering if Tom66 ever got the unit fixed and what was the solution. Anyone have any news?

Lee

Not my unit - no idea if it got fixed - OP just stopped posting.

I would suggest you start a new thread, and take some nice, clear pictures of the boards. Also, are your symptoms the same (no picture?) Any sound? Does the screen glow, even slightly? etc.

With a scope, it is much easier to debug a plasma.

[electronicsurplus]

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

Has anyone ever seen a YSUS with ONLY the top being defective? I have tried several Upper Buffers and the same result. (With the upper removed I have bottom but, no top

When Upper Buffer is installed there is no backlight nor video

Any ideas?

[newtothis]

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

All buffers received free from shorts on check?