Panasonic 27" Picture Problem

[Toasty]

Re: Panasonic 27" Picture Problem

Can you put it in test mode?

CRT anode voltage reading?

Voltage at IC pin 40?

There are several TP's around the chip in the schematic. Are there corresponding waveform and voltages given in the manual (back)?

[Krankshaft]

Re: Panasonic 27" Picture Problem

CRT anode about 29k manual says 29.25 +- 1kv so HV is ok.

I posted the available waveforms and voltage measurements at the back of the manual.

I will check the other suggestions tonight.

Thanks Again

[Toasty]

Re: Panasonic 27" Picture Problem

Excellent.

Scope pins 22 & 24. If you're getting something close to those traces, then the chip is probably shot. I say probably because there is so much going on here that something peripheral to the chip may be causing it to blank the video. That's why question as to HV.

Just curious on pin 40's volts because you were fondling the vert chip and it's a signal from there back to this chip that may have shut down this chip. I do not know if OSD bypasses that if it's shutdown.

[Toasty]

Re: Panasonic 27" Picture Problem

Missed one. Check Pin 26 too. That's tuner input apparently. Test point one and it's all the way over to the lower left at the socket on page 16. Signal should look the same as Pin 22.

I'm gonna go have my eyeballs scraped now. Will feel better after looking at these bloody PDF's.

[Krankshaft]

Re: Panasonic 27" Picture Problem

Well I carried out the tests I scoped out the tuner input and its the same signal from the test point at the tuner itself so it's a go there.

I scoped out pins 22 and 24 and when I injected a signal into the S-video port it was getting there too.

I used pin 21 as the ground reference for the IC measurements.

When I measured pin 40 I couldn't read any voltage there.

I also noticed something else funny when I adjust the brightness or any other user adjustment on the OSD it doesn't affect the raster. So I guess other then the OSD nothings getting applied to the RGB transistors.

I also posted some pics of the board what's with the gray RTV on the pins?

Some kind of insulation?

Is there anything else that I can check before I go for a new IC?

Thanks for all the replies so far.

[Krankshaft]

Re: Panasonic 27" Picture Problem

Oh yeah can someone explain what this halftoning IC near the MPU does?

I've been looking for info on it but I've come up blank just for my information.

[Toasty]

Re: Panasonic 27" Picture Problem

Gray RTV is insulation and I ran across this 2x in browsing that it must be reapplied when you're finished.

Did you check for any signal at 28, 30, 32? RGB output.

Pin 40 is "neck protector" input and it's fed from the vertical circuit, Q451 & Q452 connected to the yoke and C454 1000/25v. Although I'm not clear on what it does, perhaps it is shutting down this chip. Is it the chip killing the signal or that circuit? Per the pinout it's 0-1 volt would indicate RGB off and 1.6-3 is normal. That's why I was curious. I have no experience with this, but the circuit and your prior dealings led me back to the vertical. It's also why I asked if there was a "test" mode, because the pinout for 40 says 4-5 volts in test mode.

I remember something about halftoning being that it's the use of black or white pixels used to adjust the "shade" or intensity of a color for human eye perception. Up close, we see the pixels; from a distance, we see gray or shades of colors.

[i4004]

Re: Panasonic 27" Picture Problem

>Did you check for any signal at 28, 30, 32? RGB output.

why do you keep insisting on this?
he has the osd-only signal there(because osd appears on the screen..doesn't need to scope it...).
and?
how does that help?

pin40 and the whole rgb-blanking-but-leaving-osd thing is strange...i would expect it to blank everything, not just video...i mean if you want to protect the neck(whatever the hell that means...probably just the jargon for the vertical deflection yoke)...
would it start working if we bring external 2v dc there? prior to that, connection to vertical should be cut...
OR check components that are in that neck protection circuit...

i must admit that i can't even force myself to go thru the electric diagram pdf...
my god some things just need paper...

is the cpu hot to the touch?

oh yeah, krank, what's the crt mfr/model in this tv?

[Toasty]

Re: Panasonic 27" Picture Problem

Look at the schematic. Look at the IC pinout. OSD has its own separate outputs.

{Note that the schematic & IC datasheet pinout don't match as pointed out by PlainBill before.}

The OSD signal is generated in a separate section (MCU) of that chip, yet its drive to the CRT is derived from the connection between the MCU & the Signal Processor. The Neck Protector feeds into the signal processor section, not the MCU. I'm getting the feeling here that this circuit blanks the video if the HV rises too high. X-ray protection. Or, perhaps some other failure. Again going back to the vertical issues of several weeks ago.

<<...Time travel...>>
Takes me back to Zenith and Magnavox sets from the 70's with the 4 legged capacitor fiasco. Yes bad caps (from Taiwan) were the problem there too. These were placed to shutdown the video if HV rose too high making the set unwatchable. When these failed, they would allow HV to rise to 35-50kV+. Some provided spectacular results to the repairman when opening the set, with the neck & yoke lying in the chassis. It looked like a laser had sliced the neck off the picture tube.
Damn near bankrupted Zenith. There were 100's of thousands of sets made with these. They all had to be replaced, not to mention the destroyed sets. Literally TONS of warranty work. lol I still have a couple of those caps lying about.

>>...Okay, back from the past... ...<<

[i4004]

Re: Panasonic 27" Picture Problem

rgb issue:
indeed, it seems this chip is 2 ics that were bonded at some late stage...heh..

but that doesn't change the fact that on 28, 30, 32 RGB output he'll see what we know he'll see: just the osd.

now let me speculate for a moment: he was getting the osd even when his vertical stage was bonked, he's getting it now...ask yourself, what's the purpose of having osd on the screen when you're in the blanking mode?
well, there's none. if you're gonna protect, you shut down the rgb completely...

look at the page 21 in the chip pdf: it says
"Neck Protector: R/G/B output to zero (no signal)"
yet he has osd on rgb output...i would say that chip is damaged...what damaged it?
perhaps that vertical fault....

either way it's acting strange: kc said that g2 needs to be cranked to see if the raster is ok; well in this case there was no need because his paramater of the raster can be his osd...
i'm presuming sets that kc saw had shutdown, but the usual, total rgb shutdown, not video-blank, but osd still on, like on this frankenstein...

what is neck protection?
probably this
"At the same time the deflection currents are sensed for the protection circuits."
( http://www.alltecservicesmrtv.com/faqs.nxg/ )
ie sense of the vertical deflection current....which is probably ok now(as vertical deflection is working).
now you ask why is there no voltage on pin40? well, perhaps it is now shorted, as a result of those previous vertical issues....
if it's shorted to the ground then voltage is zero.

to that extent, its impedance is around 5kohm(page 9 of chip pdf), so perhaps that can be tested...if that is not the impedance of the circuit that connects to vertical deflection..heh...

he can test pin40 with with a dmm: if there's some voltage(on the wire leading to pin40) when pin40 is not connected (to that wire), yet it dissapears when you connect it(that wire and pin40), then it means pin40 is shorted, and that's it, faulty ic.
if there's nothing no matter connected or not, then yeah, he should inspect that neck protection circuit, ie those things leading to pin40.
if there's no voltage there chip should blank the rgb output...
<-which neatly leads us to->
but again, knowing he has osd(and had it when vertical was folded) chances are it's the chip.

but yes, he should still try to be sure...

70s?
i thought you were young?
hopefully you're not the youngster who knows all the stories from the past?
<wink>

[Wizard]

Re: Panasonic 27" Picture Problem

Open the pin 40 (can be unsolder a jumper or something like that) after the resistor network that probably pulls up and see? Be prepared to yank power cord.

Cheers, Wizard

[Krankshaft]

Re: Panasonic 27" Picture Problem

Sorry about that after scrubbing down the IC a bit it's made by Mitsubishi Electric and not Renasas. I figured the datasheets would be similar since they had the same part numbers.

http://www.alldatasheet.com/datashee...M65580MAP.html

The tube is a Matsushita model number:

M68LGL061X

The chassis is an all Panasonic line up including all the caps and the voltage regulators. The only IC not Panasonic is the main processor figures.

On the service manual the Quasar logo is next to the Panasonic one it makes me wonder if they really manufactured this thing?

Well I sent off for a new IC and some chip quik but I'll still probe around to see what's what. I'll check the RGB output signals (the video signal pins) and pay special attention to pin 40.

If this TV was normal and didn't have the micro and chroma on one IC I'd be done with this already. There is so much bonded within this IC it's annoying. I agree the bonding of the chroma / deflection and micro looked like a last minute thing.

I swear that IC is like the Thunderdome 1 signal enters no signals leave Rated R .

[Toasty]

Re: Panasonic 27" Picture Problem

Well, further discussion is moot since you have ordered the chip. Until you replace the chip, it's all speculation.

I'm hedging my bets on the vertical circuit.

Toast

[Krankshaft]

Re: Panasonic 27" Picture Problem

Nah it's just an insurance policy I had to order a new power switch for my Toshiba (Orion) from the same distributor so I just lumped it into one order.

In actuality the neck protector circuit ties to pin 1 of the vertical and oddly enough that was the pin that was cracked when the TV lost vertical sweep.

The OSD was still present in the vertical line but no video.

This is no coincidence I will look into the vertical section especially the neck protector or whatever they call it. I am getting closer.

If the stupid thing just blanked entirely (like a normal TV ) then I'd have a more methodical way of troubleshooting this.

[Toasty]

Re: Panasonic 27" Picture Problem

Was their video after the vertical resolder? Or, better question, when did video go away?

Pin 1 of vertical chip is Vcc. I'm more interested in the drive coming from yoke and across that 1000uF cap there. Check the 1 ohm 1/2 watt resistor from that cap (-) to ground on vertical chip.

There are base voltages for the transistors in the 2 neck protector circuit shown on the voltage chart. How do they compare?

[Wizard]

Re: Panasonic 27" Picture Problem

Also vertical did you replace the 100uF on that and other caps? I usually check around on the mainboard as panasonic are notorious for putting general grade caps all over.

Cheers, Wizard

[i4004]

Re: Panasonic 27" Picture Problem

>In actuality the neck protector circuit ties to pin 1 of the vertical and oddly enough that was the pin that was cracked when the TV lost vertical sweep.

the chip probably didn't like those fluctuations, so it probably gave up...

yes, we should know when video went away...
if you actually had video after the vertical resoldering, then concentrate on vertical....
if no, then on chip...

although you can still have a case of pin40 working for some time after that, and then giving up...

i would open that pin40 up and then measure resistance against ground of that chip...0ohms would suggest chip is broken...

oh yeah, is that ic getting hot? if it is, that's one more thing that points to it...

[Krankshaft]

Re: Panasonic 27" Picture Problem

No I didn't replace the pump up or any other vertical caps I did check them with the ESR meter and they are fine. But I have plenty of caps and will shotgun them just in case.

Here is the weird thing the original problem was intermittent vertical sweep it had a blank screen accept when I changed channels or brought up the menu (OSD on). So the OSD manifested itself as a vertical line which told me that this TV had a vertical shutdown to cut the video to the tube. Why it doesn't cut the OSD too is beyond me.

So I locate the bad joint desolder all the pins on the vertical IC and resolder them I reassemble the TV put the back on and go to power it up and I hear the TV power up for a second and hear the HV and deflection yokes then nothing it shuts down.

So I open it again check the board for bad solder joints or bridges nothing I put the board back in and power up the TV it powers up fine now and works perfectly. However then I notice something else I am only getting audio through one speaker when the TV is set to Stereo mode.

So to test the 2 amps I set it to Mono and I get audio through both speakers. I have cable and I verified on another set that it wasn't a network problem. I have had that happen with cable on a few channels in the past.

So I shut the set down and take a break. I come back later and miraculously the audio is restored stereo sound is back.

So hoping it was a microcontroller corruption (since the micro communicates with the external audio demodulator / CC / SAP IC) that shutting the set down cleared it I left it at that.

One day I power it up and here we are no video but OSD.

That's the whole story.

I will lift pin 40 and check for resistance the IC barely gets warm.

Based on what I have so far it's definately either vertical or this IC I can rule the tuner out because the external inputs won't display on the tube either.

I am at work at the moment so I will get Toasty's answers later tonight.

Also I did a diode check test on both of the neck protector and spot protector transistors and their nearby resistors they all check out.

[Krankshaft]

Re: Panasonic 27" Picture Problem

Those 4 transistors by the way were Q452 and Q451 for the neck protector and Q605 and Q606 for the spot killer.

I also checked the RGB signal transistors that take the RGB video signal and the RGB OSD off the chip they checked out as well.

Oh yeah and i4004 I don't mean RGB in the video signal sense I mean the red, green, and blue color signals. Sorry for the confusion.

For some reason the IC doesn't mix the OSD and video signals on chip and does it outside.

I'll check the service manual when I get home and see if they list voltages for those transistors.

Thanks for all the tips again. I can see the light at the end of the tunnel.

[Toasty]

Re: Panasonic 27" Picture Problem

>>I can see the light at the end of the tunnel.<<
It's just the headlight of the locomotive.