Panasonic 27" Picture Problem

[Krankshaft]

Re: Panasonic 27" Picture Problem

Well I've FINALLY got a bite here.

First off I lifted pin 40 and powered the TV up no change. There was no short between pin 40 and the trace it has about 35 M ohms or so of resistance. So I soldered the pin back down.

The manual did have voltages for both the neck protector transistors.

The neck protector transistors:

Q451: Manual Voltages

B: 0.59
C: 0.00
E: 0.00

Actual On Board

B: 0.663

Q452: Manual Voltages

B: 0.00
C: 2.49
E: 0.00

Actual On Board

C: 400mv Building up to this then falling down to around 200mv and restarting again.

I think this is what's dragging down the line and causing the IC to blank out.

Q453: Manual Voltages

B: 0.00
C: 8.65
E: 0.00

Actual On Board

C: 8.69

The spot killer transistors:

Q605: Manual Voltages

B: 4.23
C: 0.00
E: 4.21

Actual On Board

B: 4.12V
E: 3.93 It slowly rose to this voltage

Q606 Manual Voltages

B: 0.00
C: 3.63
E: 0.00

Actual On Board

C: 4.08 V

I also checked the line that the neck protector and spot killer connects into the bold line and one end leads to the power supply transformer. I measured across C560 a bipoloar lytic and got around 4.96 volts with the TV in standby and 4.05 with the TV on.

The IC datasheet says for pin 40:

0.0 - 1.0 RGB off
1.6-3.0 Normal

I did consider supplying it externally with my digital bench supply but decided against it.

So it seems that the IC is getting blanked most likely because of Q452 but why wouldn't it be receiving the proper collector current?

Now it's personal with this thing .

[PlainBill]

Re: Panasonic 27" Picture Problem

Well I've FINALLY got a bite here.

<SNIP>

I did consider supplying it externally with my digital bench supply but decided against it.

So it seems that the IC is getting blanked most likely because of Q452 but why wouldn't it be receiving the proper collector current?

Now it's personal with this thing .

You're looking at it from the wrong direction. Look at Q451 and Q452. The current source for Q452 is IC001 through R475. The base current for Q452 is comes from the VCC1 supply for IC451 - the vertical output driver. BUT Q451 is supposed to hold the base of Q452 at 0V. If that voltage goes too high, Q452 turns on, blanking the video.

Now I see several possibilities VCC1 might be too high - highly unlikely, that's a power supply voltage. R463 might have dropped in value - equally unlikely. The base voltage of Q451 might be too low, turning Q451 off, so the base voltage of Q452 rises. EXCEPT that you already measured that voltage, and it is very slightly high. Now Q451 might be leaky, or IC001 pin 40 might be at too low of a voltage. It's probably got an internal pull up resistor.

Now I see three ways to troubleshoot this. The easy way is to lift one end of R475 and see what the voltage is at IC001 pin 40. If it's too low the problem is either IC001 or some contaminants on the board. If IC001 pin 40 goes way up in voltage you know it's not IC001. In that case, check the base voltage of Q452. If it's 0V, Q452 is bad. If it's .7 volts, look at the signal coming into the base of Q451. QED

Oh, if you look at Page 16 (first page of the A board schematic), take a look at TP1. It appears to me you can safely drive IC001 Pin 40 to 2.5 volts.

Aren't transistors fun?

PlainBill

[Krankshaft]

Re: Panasonic 27" Picture Problem

Yes they're mine numbingly interesting .

Well I removed the resistor and measured pin 40 got .660 volts. No RGB so then I sent 2.5 volts to pin 40 with my power supply still zilcho no current draw indicated on the power supply either and still no video.

I think the IC is toast.

I've already checked the 9 volt, two 5 volt, and the 3.3 volt voltage regulators so the supplies are fine.

[Toasty]

Re: Panasonic 27" Picture Problem

>>It's probably got an internal pull up resistor.<<
Indeed it does.
Page 9 of the Renesas or Page 23 of the Mitsubishi sheet show the internals there. If the protect circuit fires (Q452 on), it will drag the voltage down.

What puzzles me is that the measured voltage at pin 40 was 0 (post 25) and here he's seeing .2-.4 volts on the other side of R475. How do you get voltage there (C of Q452) from a 0 volt source?

I quick built the internal circuit (2 resistors) and the external with R475 and a 2sc945 subbing for Q452. Vcc of 5 volts on the internal divider. Applying current to the base of the transistor thru a 1.3k resistor made it fire causing the voltage at "Pin 40" to drop. The collector voltage was .1 volt. Expectedly, shorting collector to emitter with no base voltage showed the same results.

I do not believe the neck protector is presently "firing". If it were, I'd expect to see some + voltage on the base of Q452 from the voltage drop across Q451 being "on".

I concur with Bill's evaluation.

If you lift the Q452 collector side of R475 and see -
a) 5 volts or so, then Q452 is shorted
b) 0 or low volts, then IC001 is bad

Toast

[PlainBill]

Re: Panasonic 27" Picture Problem

Yes they're mine numbingly interesting .

I think the IC is toast.

I've already checked the 9 volt, two 5 volt, and the 3.3 volt voltage regulators so the supplies are fine.

Yup, I agree with you. Forcing pin 40 to 2.5 volts confirms it. That eliminates all external components on pin 40.

PlainBill

[Toasty]

Re: Panasonic 27" Picture Problem

Okay. What killed it? Did the vertical problem from weeks ago do some damage? Or, is there another issue?

Replacing this chip may result in the same failure...?

Before you rip it out, and after you get the RTV off, reflow the whole chip. Just for sh**s and giggles.

[Krankshaft]

Re: Panasonic 27" Picture Problem

I've got nothing to lose I'll reflow it and give it a shot.

A fair amount of pins on one side have RTV on them so I'll remove the RTV and sub hot glue for a quick test. It should insulate well enough for a few second test and is much easier to remove. I have plenty of RTV from all the auto work I do so I'm set for the new IC.

Maybe the set not powering on for a few cycles after the vertical resolder was a clue I also couldn't get a stereo signal (only through one speaker and very weak in the other).

That may have been the micro not communicating properly with the external audio proccessor IC. As for not booting up since that IC is vital to the operaton of the horizontal section that's pretty self explanitory.

It may have been a warning that I ignored.

Anyhow thanks for all the help and sticking with me through this.

Believe me it's taking alot of control not to introduce this set to my 10 pound sledge .

[i4004]

Re: Panasonic 27" Picture Problem

i'm slightly dissapointed because the ic-gulity sayers were right all along...me included...heh...

i've mentioned bringing 2v to pin40 here
https://www.badcaps.net/forum/showpo...9&postcount=28
but i didn't insist because i didn't really know the waveform(multi-page electric diagram pdf? scary! and i don't have printer)...seems bill checked that one for us...and that's great...

chip probably become marginal the first time vertical problems appeared, and then failed completely after some time..

[Toasty]

Re: Panasonic 27" Picture Problem

Okay, but why the neck protector circuit? Why not the video section? Or the vertical or something else that could've been spiked?

There's no voltage applied to that pin, it supplies a voltage and reacts accordingly. It's protection action is to "go to ground" thru the 470 ohm resistor and Q452 C-E.

If reasoning serves from the IC schematic, it trips and shuts off the video. Then stays latched until a power cycle occurs. So the MOSFET on that pin got toasted (sitting behind static and spike protection) and is stuck on or off?

Yeah, you can swap the chip out, but explaining what caused it to die this way....?

Back on post 13 kc8adu said "...these chips seldom fail and when they do ist usually due to lightning...".

[Wizard]

Re: Panasonic 27" Picture Problem

Panasonic and JVC is uber sensistive to power surges (not just lightning).

How I know, I rebuild these many times before.

Cheers, Wizard

[PlainBill]

Re: Panasonic 27" Picture Problem

Okay, but why the neck protector circuit? Why not the video section? Or the vertical or something else that could've been spiked?

There's no voltage applied to that pin, it supplies a voltage and reacts accordingly. It's protection action is to "go to ground" thru the 470 ohm resistor and Q452 C-E.

If reasoning serves from the IC schematic, it trips and shuts off the video. Then stays latched until a power cycle occurs. So the MOSFET on that pin got toasted (sitting behind static and spike protection) and is stuck on or off?

Yeah, you can swap the chip out, but explaining what caused it to die this way....?

Back on post 13 kc8adu said "...these chips seldom fail and when they do ist usually due to lightning...".

One of the myths is that solid state circuits (ICs) never fail by themselves. Even if poor design doesn't leave them sensitive to voltage spikes, they can still fail. Sadly, one of the causes is the 'lead free' fad. This has been discussed at length, but the fact is that the tin/lead alloy we call solder is a very good bonding agent for electronic components. Remove the lead and tin has the property of growing 'whiskers'. Whiskers that can short out ICs.

I agree, knowing WHY a chip failed is important. There is nothing like watching the $28.00 chip you installed going up in a puff of smoke to make you wish you had checked a little more carefully. But sometimes all you can do is say 'stuff happens.'

PlainBill

[i4004]

Re: Panasonic 27" Picture Problem

>Okay, but why the neck protector circuit? Why not the video section? Or the vertical or something else that could've been spiked?

well, he had vertical pumping in/out (on/off) because of bad solder joint he fixed originally...

ie he said
"I had a vertical problem a few weeks back but it just turned out to be the power pin on the vertical IC cracked."

so his vertical was essentially a bit on, then a bit off, etc.

i don't think you can be sure what happen to voltage on pin40 if supply for vertical ic is rapidly switched on/off...

also, if ic is fed from the same supply as that vertical ic....then perhaps it got it...

>If reasoning serves from the IC schematic, it trips and shuts off the video. Then stays latched until a power cycle occurs. So the MOSFET on that pin got toasted (sitting behind static and spike protection) and is stuck on or off?

hehe, yeah, it has awesome protection with elements inside the chip...heh...
resitor in the chip, well, yeah, why wouldn't it act as a big 5w resistor, or a proper fast fuse...
<wink>


>Yeah, you can swap the chip out, but explaining what caused it to die this way....?
>Back on post 13 kc8adu said "...these chips seldom fail and when they do ist usually due to lightning...".

explaining exact reasons chip die can be hard...sometimes there will be no reason whatosoever...it'll just die because production was such that that chip perhaps got a slightly too big dust particle on wrong spot, or something similarly silly...

and now with wizard's explanation you know one more reason...
offcourse user should make sure surges don't reach the devices...
we know power companies won't...

[PlainBill]

Re: Panasonic 27" Picture Problem

and now with wizard's explanation you know one more reason...
offcourse user should make sure surges don't reach the devices...
we know power companies won't...

I once had lightning strike very near to the house - no perceptible lag between the flash and the thunder. Four pieces of equipment were damaged. A 19" Funai TV in the bedroom (total loss), a 27" TV in the living room (blew the OSD chip!, easy repair), a crappy 'hands free' telephone from Radio Shack, and a cheap corded phone that wasn't even hooked up. Both TVs were on cheap surge suppressers, the phone line was not protected. But the kicker was the phone that wasn't even hooked up. You do what you can, Thor will do whatever he pleases.

PlainBill

[Wizard]

Re: Panasonic 27" Picture Problem

Stop that instant i4004! You are gibbering.

IC, diode, transistors are mostly composed of silicon with very thin layer of insulating oxides (mosfet/fet) or n and p junctions layers (transistors/diodes). What happens is when there is a flaw in the matrix, excessive current or excessive voltage that breaks through the breakdown threshold cause layers disurpted and melt into short circuit or blow open (even at nanometers size) rendering the useful devices useless.

Resistors and capacitors, inductors of any types fail by faulty manufacturing or excessive current or too high voltage, sometimes too low voltage (sometimes that happens in faulty circuit designs! Very high value resistor come to mind in the startup circuit of some SMPSes). Heat beyond their tolerances or extreme cold will do that.

Lightning works their destruction in mysterious ways.
One guy had a circuit board loaded with components but the traces were totally blown off leaving no solder with no traces with components still installed and aren't burnt off. Weird.

I have few circuit boards that had biggest traces blown open leaving fine traces intact.

Cheers, Wizard

[Toasty]

Re: Panasonic 27" Picture Problem

@Krankshaft - If you go the "Way of the Sledge", be sure to get it on video!!

[i4004]

Re: Panasonic 27" Picture Problem

>What happens is when there is a flaw in the matrix, excessive current or excessive voltage that breaks through the breakdown threshold cause layers disurpted and melt into short circuit or blow open (even at nanometers size) rendering the useful devices useless.

nope, that's wrong. like plain bill and i have said ics can fail for no apparent external reason(excessive voltage or current).
which means it's something inside them, and only time when that can happen is during manufacturing...
this doesn't happen a lot, but it does happen occasionally...

it's also wrong to say it's rendering devices useless: they can be partially damaged, so(for example) it takes some time for them to start working properly(i had such case with philips sync ic). this ic in krank's tv was partially damaged, obviously...

so no, it's not like you can always explain it by lightning, overcurrent or overvoltage...
sometimes there'll be none of that yet ic will still fail...
but it's rare, yeah...

[Wizard]

Re: Panasonic 27" Picture Problem

>>What happens is when there is a flaw in the matrix, excessive current or excessive >>voltage that breaks through the breakdown threshold cause layers disurpted and >>melt into short circuit or blow open (even at nanometers size) rendering the useful >>devices useless.

>nope, that's wrong. like plain bill and i have said ics can fail for no apparent external >reason(excessive voltage or current).
>which means it's something inside them, and only time when that can happen is >during manufacturing...
>this doesn't happen a lot, but it does happen occasionally...

Watch what you have *said*.

Look at my words again:

What happens is when there is a **flaw in the matrix**, excessive current or excessive voltage that breaks through the breakdown threshold cause layers disurpted and melt into short circuit or blow open (even at nanometers size) rendering the useful devices useless.

**flaw in the matrix** is what I mean by flaw in the semiconductor matrix (not IC or transistor) that eventually develop or instantly that leads to failure.

I used commas and "and" to give list of possiblities that can happen to a manufactered semiconductor devices. Failures that destory the semiconductor devices: Surges like lightnings, poor cooling or no cooling, excessive voltage, excessive *CURRENT* or even physical blow or excessive pressure to the device thereby fracturing brittle semiconductors.

Passive components are no immune to these too. Badly designed circuit fail quicker also.

There is NO such as "for no apparent reason" failure. It either fail or not.

Cheers, Wizard

[i4004]

Re: Panasonic 27" Picture Problem

"flaw in the matrix" means that all ics made from that mask are equally affected and are all marginal quality.

i'm not thinking about those when i say that we can have marginal quality on 1 piece per 1000 or 10000 produced pieces...

i'm thinking about freak accidents where something contaminates the silicon in a time/place where such contamination can cause further damage later on...


and there's nothing predictable about those...and they don't need to be triggered by

"Surges like lightnings, poor cooling or no cooling, excessive voltage, excessive *CURRENT* or even physical blow or excessive pressure to the device thereby fracturing brittle semiconductors."

or whatever external reason you can think of...


ie i don't think manufacturing process is perfect...even if you have perfectly fine "matrix".

[Wizard]

Re: Panasonic 27" Picture Problem

Stop pulling out of context please.

]"flaw in the matrix" means that all ics made from that mask are equally affected and are all marginal quality.

Rare that can happen but not in the context of this discussion. What we are discussing number of things that cause semiconductors to fail. PERIOD.

i'm not thinking about those when i say that we can have marginal quality on 1 piece per 1000 or 10000 produced pieces...

That's common. I see this all the time when I repair stuff at work. We had to replace these. Usually early in the life of the products within warranty and very old stuff.

i'm thinking about freak accidents where something contaminates the silicon in a time/place where such contamination can cause further damage later on...

Not in this context and I have already said this already. This is covered in seperate topic and usually I see this in bulletins where a chip had to be replaced by warranty or by customer's expense. Such as life.

and there's nothing predictable about those...and they don't need to be triggered by

"Surges like lightnings, poor cooling or no cooling, excessive voltage, excessive *CURRENT* or even physical blow or excessive pressure to the device thereby fracturing brittle semiconductors."

or whatever external reason you can think of...

This have happened, period! You haven't been a repair tech, I have and others have here have said same thing.

ie i don't think manufacturing process is perfect...even if you have perfectly fine "matrix".

This is PRECISELY why what costs so much for chips especially first run semiconductors to work out issues and get it all good then price fall as number increases in chips. Sometimes they got lucky and pump out really good chips that sometimes forced them to lock out something in past (like Intel and AMD had to do so while ago).
Semiconductors always have flaws regardless. This is why they test them and mark them bad, before cutting the dies free from slice and some grade them, best for most demanding use, and using lesser on relaxed conditions like less voltage diode/less current, cpu less speed locked in etc.

The rest that doesn't pass usually is not disposed of, these dies get sold to the market as rejects and those are where generic parts uses these and that what are upsetting us like generic memory not good, fake transistors that doesn't perform fully, wrong specs for specific use even it is marked as such.

I have seen these generic and DID give problems so I refuse to use these as such. Again this is part of whole picture but this is not in the context. We were talking about conditions what causes these stuff to fail that's all.

Once again:

Lightning/surges/static discharges which is common, which is another word for excessive voltage or current.

Impacts/mechanical stress.

Heat or too extreme cold. Not just cooling issues which is part of packaging/end user issues.

Excessive current or excess voltage. Used in cheap design that is beyond semiconductor's datasheet specified or due to chain of failures, like failing flyback or a open capacitor caused this device to fail due to excessive current or voltage.

Flaw in the semiconductors is tested for and cut out but few do exist and usually develop a failure early on or late in the life of the semiconductors (bell shaped graph).

Cheers, Wizard

[i4004]

Re: Panasonic 27" Picture Problem

Flaw in the semiconductors is tested for and cut out but few do exist and usually develop a failure early on or late in the life of the semiconductors (bell shaped graph).

we agree.
rest were the misunderstandings.

(i wrote bigger reply with details etc. but server connection was lost, so it's gone...)