Panasonic TNPA5081 rebuilt, poor image

[Alastair E]

Re: Panasonic TNPA5081 rebuilt, poor image

Tom, are you saying the "shorter oscillations" (which progressively increase in width) should be the same height as the tallest one? The scope is set at 5V/div and my probe says 10x, so it is really 50V per div. So the tallest spike is above 400V. If that is the case, the shorter one may be about 300V. Are you saying this need to be 400 as well? Making sure this is what you mean by stunted.

True--Your scope is showing 400 odd V --P-P.

Meaning that you're showing a signal going Minus 200 odd volts to 200V Positive--ish.
As Tom says, the signal is swinging around the 0V point, both positive peaks and negative troughs....

Therefore, the '0' Volts point on the screen is approx halfway down,--the middle, (actually by the look, 1 large graticule division below middle, giving your sub-fields about 50V amplitude, and not enough........

Give you an idea--Where on the Scope-screen is the trace when you remove the signal from the scope....? I'll bet is approx halfway down screen, (actually 1 div below centre-line--ish.)

The voltages across the panel, from the SS side to the SD side are AC voltages--in opposition, one side Minus, other Positive then it reverses, but these AC voltages are derived from DC sources--hence the need for all the switching transistors. The voltages HAVE to be AC as they are insulated from the gas inside the panel by the dielectric layer, applying DC will give no gas ionisation or light production.

[tom66]

Re: Panasonic TNPA5081 rebuilt, poor image

The AC is used to reverse the programmed wall charge on each cell on each sustain cycle. You can get light from DC, under glow discharge, but this is across the whole panel.

[Alastair E]

Re: Panasonic TNPA5081 rebuilt, poor image

How come, Tom?

The Electrodes are insulated from the gas of the panel by the dielectric, therefore, no current can pass....

AC works due to the capacitance between electrodes, hence current flow....

The cell charge is removed by the reset-ramp....

[tom66]

Re: Panasonic TNPA5081 rebuilt, poor image

The gas still conducts because it has an abundance free electrons.
Glow discharge - think neon lamp, they work on DC. Similar principle.

[Alastair E]

Re: Panasonic TNPA5081 rebuilt, poor image

Aye--I agree Neons work--glow discharge--On DC because the electrodes are in Contact with the gas.
In a Plasma Panel--They are Insulated from the gas......

[tom66]

Re: Panasonic TNPA5081 rebuilt, poor image

The glow might be from the address electrode, as that is in contact with the gas. If you bias a PDP with a few hundred volts, it will also glow, regardless of wall charge or ac bias.

I'll try and dig out a Panasonic service manual on this. Very old one, but good explanation of the basic principles.

[Alastair E]

Re: Panasonic TNPA5081 rebuilt, poor image

Ah--Right, Now you're talking, Didn't realise the Address electrode was not decoupled by dielectric-layer.
I forget which, but a Neon will only glow predominantly on one electrode when on DC.....

[tom66]

Re: Panasonic TNPA5081 rebuilt, poor image

I know the Kuro 9G panels use Townsend discharge region (DC glow discharge) with spatial discharge (also DC) for the 1st & 2nd SF (28 total SF!!) - see this X-drive waveform from my 50" 9G panel:

[keats11]

Re: Panasonic TNPA5081 rebuilt, poor image

So I have to now try to deduce from schematic what might be causing ths stunting of the sustain waveform. I have attached part of the schematic that shows the output transistors driving this signal, but I cannot figure out what causes these sustain waveforms and how it increases in width etc. If you guys have a clue what to look for let me know. The good thing is I have the whole schematic for this board.

[tw2005]

Re: Panasonic TNPA5081 rebuilt, poor image

If it were me I'd look at LIN and HIN signals in , then HO & LO out at both IC501,521 and see if anything is missing. Not sure about Vs.

[keats11]

Re: Panasonic TNPA5081 rebuilt, poor image

Gone bad to worse. Noticed one of the FET driver ICS was not soldered perfectly straight, so fired up the hot air station and set it straight. Now it just does 7 blinks and shutdown. No blown FETs. This is where I was just a couple of days ago, I thought I had fixed it after I had changed a diode, but may be not. Trying to figure of from block diagram what causes 7 blinks and sort of back trace. The training document says:
"The SOS7 circuit monitors the panel, the scan circuit output, the 15V_F, the scan_pro, Vscan, and the physical connection between the SC board and the SM board (CHA)."

It is not the last one.. does anyone know the diff between scan o/p. Vscan and scan_pro?

[Alastair E]

Re: Panasonic TNPA5081 rebuilt, poor image

Scan o/p would be the main drive power from SC out to the buffers.

VScan is a supply derived on the SC for the buffers, a floating supply--I think...

Scan_pro, Assuming 'scan protection'

[keats11]

Re: Panasonic TNPA5081 rebuilt, poor image

Ok guys eliminited 7 blinks, back to washed out image. Some how I got the inkling (I think it was God) to check the tiniest diode 702. I ad mounted it in a vertical direction as supposed to horizontal, because there were 4 solder dots in that location to confuse things. With the diode planted right, back to the washed out image. But I am still glad that this sucker is as alive as it is.. and seems stable too. Will keep chasing, praying..

[keats11]

Re: Panasonic TNPA5081 rebuilt, poor image

More updates just in case anyone is following this closely. I was trying to look at the output signals (I think pin 6,7,8) of IC driver 501 to see is these look fully developed, when I heard a pop and many FETS bew again. Replaced the FETS, not back to 7 blinks, but also I noticed the diode-reading between the Gate-Emitter of Q401/402/403 do not make sense (about 0.5V in both directions). The FETs are not shorted Drain-Source, so I am thinking I have a bad Q501. This may have been the reason the VFG waveform was stunted to begin with. I have ordered the part from mouser.. lets wait till it gets here for more updates.