How to Troubleshoot a Plasma TV (p50s602) with an Oscilloscope

[Robb]

Re: How to Troubleshoot a Plasma TV (p50s602) with an Oscilloscope

Thank you for confirming and thank you for all the help...Hiatchis are buggers to work on.

[tom66]

Re: How to Troubleshoot a Plasma TV (p50s602) with an Oscilloscope

EXT TRIG can be used with a 3rd signal which is not displayed to trigger off that, can be handy if you need a 3rd channel for triggering but don't care about what waveform is actually there.

[Robb]

Re: How to Troubleshoot a Plasma TV (p50s602) with an Oscilloscope

Back to the more general topic of oscilloscopes. Is the External Trigger Input probe supposed to be connected to a separate signal of which the Ch1 or Ch2 probe is reading? I'm beginning to think that mine might work but I just don't know how to use it yet.

[Robb]

Re: How to Troubleshoot a Plasma TV (p50s602) with an Oscilloscope

It looked like POWER 1, POWER 2, Vcego & Vsago voltages were low. Although the wording is difficult for me to understand the service manual says:

"(3) PoWER_1 : High PSU outputs +5.6V.
and STBY+5V changes from 5.1V to 5.6V.
(4) PoWER_2 : High PSU outputs +17V and Audio+17V.
(5) Vcego : High PSU outputs Vcc+5.1V for PDP Module.
(6) Vsago : High PSU outputs Va and Vs for PDP Module.
(The voltage values of Va and Vs are indicated to the sticker on the PDP Module.)

If any control signal does not rise, PSU cannot output the voltage.
PoWER_1/2 : not rise ----- Main board trouble
Vcego/Vsago : not rise ----- PDP Module (Logic board) trouble
However, Vcego rises when PNLRST/CPUgo (P901 [43] at Main board) is High, and
Vsago rises when PNLoN/PDPgo (P901 [42] at Main board) is also High."

Maybe the above highlighted voltages for are not what I should be finding when I measure with a DMM but they appear to be low. I was reading "If any control signal does not rise, PSU cannot output the voltage" as an indication that the voltages should rise to the highlighted voltages, however, they ARE rising just not to what I am expecting them to be.

In any event, I'm embarrased to say it but I think I fried my XSUS while measuring the voltages on it when my hand slipped and shorted Vs to an unknown point on the XSUS. Now the blue LED is blinking 2 times (instead of 5) and when the screen briefly lights up it is noticably dimmer.

There are no components at the point I shorted and there is no schematic in the service manual. I think this TV may have beaten me. Below are pics of the damage.

Oh the agony of defeat.

[tom66]

Re: How to Troubleshoot a Plasma TV (p50s602) with an Oscilloscope

I'm well past my knowledge point here, but why do you think a problem with "POWER 1, POWER 2, Vcego and Vsago" exists? Help me understand your train of thought.

[Robb]

Re: How to Troubleshoot a Plasma TV (p50s602) with an Oscilloscope

Are we done with the oscilloscope? If so maybe we should return to the original post.

[Robb]

Re: How to Troubleshoot a Plasma TV (p50s602) with an Oscilloscope

The Va signal on the oscilloscope was a DC horizontal line that jumped up and then quickly returned to where it started from. The Va reading from a DMM was 67.0V and held for a little while before slowly diminishing I guess due to the capacitors. The panel says the Va should be 66.8V.

Other voltages:
When off;
STBY = 5.05V
AC CLOCK = 1.1V-1.5V

When on;
Vs = peaks @ 184V
Va = peaks @ 68V
Vcc = peaks @ 5.1V
AUDIO 17V = stays @ 17.2V
+5.6V = stays @ 5.5V
+5.6V = stays @ 5.5V
AC CLOCK = varies from 1.72V-1.27V
STBY = stays @ 5.6V
POWER 1 = stays @ 4.3V
POWER 2 = stays @ 3.2V

Vcc 5.1V = 5.1V
Vra = 1.7V
Vrs = 1.42V
Vcego = 3.0V
Vsago = 3.0V
AC OFF = 0V

(Va) = 67V
Va = 67V
Vcc 5.1V = 5.1V
Vs = 184V
Vs = 184V
Panel says Va = 66.8V & Vs = 184.1V

The service manual say:
*) Power-On control signals for Power Supply Unit
(1) AC power : Supplied
PSU outputs STBY+5V.
(2) Power Switch: ON : or Remote Power button : ON
PoWER_1 rises up.
(3) PoWER_1 : High PSU outputs +5.6V.
and STBY+5V changes from 5.1V to 5.6V.
(4) PoWER_2 : High PSU outputs +17V and Audio+17V.
(5) Vcego : High PSU outputs Vcc+5.1V for PDP Module.
(6) Vsago : High PSU outputs Va and Vs for PDP Module.
(The voltage values of Va and Vs are indicated to the sticker on the PDP Module.)

If any control signal does not rise, PSU cannot output the voltage.
PoWER_1/2 : not rise ----- Main board trouble
Vcego/Vsago : not rise ----- PDP Module (Logic board) trouble
However, Vcego rises when PNLRST/CPUgo (P901 [43] at Main board) is High, and
Vsago rises when PNLoN/PDPgo (P901 [42] at Main board) is also High.


Looks like POWER 1, POWER 2, Vcego and Vsago might be the problem, huh?

[tom66]

Re: How to Troubleshoot a Plasma TV (p50s602) with an Oscilloscope

It looks to me like your SUS waveforms are both more-or-less correct; at least, the major parts are there.

Next step, check your Va voltage is holding steady. I don't know what each of your test points on the ABUS should measure, because Hitachi provide really minimal documentation...

[Robb]

Re: How to Troubleshoot a Plasma TV (p50s602) with an Oscilloscope

Is it normal for the ABUS Test Point signals to vary? The YSUS and XSUS were fairly similar when testing different points but the ABUS produced a variety of signals as shown below. Both the Upper ABUS and the Lower ABUS boards had similar variations.

Oscope Settings: 20mV/Div, 5mSecs/Div & 10X probe

[Robb]

Re: How to Troubleshoot a Plasma TV (p50s602) with an Oscilloscope

Thank you for this invaluable hands on lesson. I lowered the TIME/DIV to 5mS and the position of the vertical scale (maybe a little too much), pulled out the vertical 5X Magnify knob and turned it down, adjusted the FOCUS and partially pushed down on the camera's button before taking the photo below.

[tom66]

Re: How to Troubleshoot a Plasma TV (p50s602) with an Oscilloscope

Zoom in on that spike at the beginning of each pulse if possible and adjust the FOCUS control of the scope.

[Robb]

Re: How to Troubleshoot a Plasma TV (p50s602) with an Oscilloscope

Correction: On the XSUS, I measured where the ribbon connects to the XSUS board & at few other spots on the output side of the board (they all looked about the same).

On the YSUS, I've tested at the YSUS to Y-buffer connection, traces leading to the ICs on the Y-buffer and where the Y-buffers connect to each other and they all produce the same wave as pictured below.

[tom66]

Re: How to Troubleshoot a Plasma TV (p50s602) with an Oscilloscope

Need to figure out the actual sustain board output, probably one of those wide (6+ pins) traces on buffer board. Try one or the other.

[Robb]

Re: How to Troubleshoot a Plasma TV (p50s602) with an Oscilloscope

Yup. Boards are labeled X-SUS & Y-SUS. On the XSUS, I measured where the ribbon connects to the YSUS board & at few other spots on the output side of the board (they all looked about the same). On the YSUS I measured at the TPs that I mentioned earlier, TP80, TP80E, TP85, TP85E, etc.

[tom66]

Re: How to Troubleshoot a Plasma TV (p50s602) with an Oscilloscope

Are you sure you got those the right way around? 1st wave looks like a bad Y-sus wave, 2nd looks like OK X-sus.

[Robb]

Re: How to Troubleshoot a Plasma TV (p50s602) with an Oscilloscope

Was that with a 10X probe?

Yes

[tom66]

Re: How to Troubleshoot a Plasma TV (p50s602) with an Oscilloscope

Was that with a 10X probe?

[Robb]

Re: How to Troubleshoot a Plasma TV (p50s602) with an Oscilloscope

Not sure what your original fault was

The TV powers on and displays maldischarge (deepspace-like static) for 3 seconds then turns off leaving a 5 blinking LED code.

[Robb]

Re: How to Troubleshoot a Plasma TV (p50s602) with an Oscilloscope

The XSUS was set at 10mS/Div & 2V/Div

The YSUS was set at 10mS/Div & 5V/Div

The measurements were taken on Ch1

With a DMM the XSUS measured 35V and the YSUS started at +66V then went to -140V.

The poor focus may have been from the camera.

Not sure if this is relevant but there is a Test Point near the power input to the YSUS that I can't get either a DMM voltage or an oscope reading on.

I must say I'm having alot of fun probing around. Thanks for all the feedback. It wouldn't be as fun without it.

[tom66]

Re: How to Troubleshoot a Plasma TV (p50s602) with an Oscilloscope

You need to adjust the FOCUS control on the scope to improve the sharpness of a trace. What V/DIV are those at?

You only use EXT TRIG IN with the external trigger input; use CH1 trigger and CH1 for main input for now.