Panasonic PVC-2021 Vertical Deflection

[Krankshaft]

Well its time for me to ask some questions for a change .

I have on my bench a Panasonic 20" TV/VCR when it came in it wouldn't shut off and emitted a burning smell.

There was also evidence of liquid spillage in the set nothing major a few drops here and there which caused corrosion across a few jumper wires I quickly sanded them off and blew off the dust with compressed air.

Upon quick inspection the main relay was stuck in the ON position and burned a nice hole through its case. When I desoldered it the pins on the contact side literally fell out.

Anyhow I ordered a new relay from Panasonic installed it and the TV worked great. It turned on and off and all of the functions worked.

However when cold the TV exibits vertical deflection problems the top and bottom of the screen is squished by 1" in other words a vertical height problem.

As the set warms up the vertical deflection expands to the point where it fills the whole screen.

At first I suspected capacitors however since this TV is a Panasonic it has all Matsushita caps with a few Rubycons in the mix I wasn't really confident that they were the cause.

However I took out my ESR meter and measured the lytic caps in the vertical section and they were fine but I replaced them anyways.

What a suprise still poor vertical deflection.

I then looked for bad solder joints touched up a few including resoldering the vertical IC still nothing.

I have attached a schematic of the vertical section.

I replaced the following caps C414, C402, C408, C409, C418, and C401.

I have done everything but replace the deflection IC.

I have ordered one along with a can of freeze spray so once the set is warmed up I can hopefully freeze the culprit which will cause the deflection to shrink.

Does anyone have any other ideas?

Thanks for any help in advance this problem is so annoying and is driving me nuts.

I'll take a horizontal line any day over this .

[Krankshaft]

Re: Panasonic PVC-2021 Vertical Deflection

Oh I almost forgot here are some pics of the vertical deflection when the set is cold and after it has warmed up.

Once when I ran it for an extended period it completely cleared up with no visible banding however when the set cools down again the process repeats itself.

[i4004]

Re: Panasonic PVC-2021 Vertical Deflection

had the simillar thing with a particular philips set, but much more extreme....
it was fun to watch how heating the ic with a hairdryer(used a piece od cardboard to heat just the ic) extends the image height rather quickly....

http://bbsrv.wks.gorlaeus.net/~i4004...nimation10.gif

i didn't change that ic because that tv also didn't have the sharpest image around(rather old tube), and it's 55cm so it's too small for me...

chances are that changing the ic will heal it.
(one you eliminate all causes, the one remaining....)

[Krankshaft]

Re: Panasonic PVC-2021 Vertical Deflection

Thank you I needed to hear that.

I ESR metered the vertical circuits like crazy no caps had high ESR.

I'm not suprised Panasonic makes good caps and personally I didn't expect to find any bad ones.

[kc8adu]

Re: Panasonic PVC-2021 Vertical Deflection

i had a 32" panasonic in last week.
same problem
was bad solder joints and a 220@35 near the ic.

[Krankshaft]

Re: Panasonic PVC-2021 Vertical Deflection

I already replaced that cap that was C418 on the schematic and all of the others in the vertical circuit even though my ESR meter said that they were fine.

I went over every joint in the vertical section with a magnifying glass and even resoldered the vertical output ICs pins nothing.

I guess Murphy doesn't want to give me this one so easily.

That is whats frustrating me this sounds like a cap problem as the temperature rises the ESR falls. But the more I look into the caps with my ESR meter the more wrong I think I am.

Frustrated I decided to do what i4004 did I took a piece of cardboard and enclosed the U shape of the vertical IC heatsink to concentrate the hot air.

The 4 caps in the U shape of the vertical heatsink and in the path of this hot air were replaced with new ones so that I could be sure that they weren't reacting to this test.

Then I heated up the vertical IC with a blow dryer with the set running and slowly but surely the vertical height increased until I got it to deflect 1/8" from the end of the top of the screen.

It probably would have gone further to the top of the screen if I kept at it but I didn't want to roast the new caps or activate the thermal shutdown on the IC.

KC8 how often to you come across thermally intermittent vertical ICs?

[Wizard]

Re: Panasonic PVC-2021 Vertical Deflection

Yes. Replace with LA7838. More capable IC.

And go over supply caps that is near flyback transformer for the vertical B+ power.

Cheers, Wizard

[Krankshaft]

Re: Panasonic PVC-2021 Vertical Deflection

Well I shoved this one in the closet and forgot about it .

After that other PITA Panasonic with the bad IC this was a cakewalk.

It turns out I screwed up where the thermal based issue was it WAS in the PSU just like you said Wizard.

So I blast the secondary side of the PSU with cold spray and the vertical deflection shrinks instantly. Heat it with a blow dryer and it expands rapidly. Finally a BITE!

This is all because of a stupid regulator circuit design read on.

So I narrow it down to a zener diode controlled 12 volt regulator it's comprised of 2 resistors a zener diode and a NPN transistor. This is just one notch better than a crappy zener diode only regulator.

Zener diodes are sensitive to temperature which caused the output voltage to fluctuate with temperature which explains the the expanding and collapsing deflection.

I have included the schematic for the PSU section the regulator transistor is Q1051 the zener is D1054 and the two resistors are R1052 and R1053.

The regulator is supplied by a 14 volt source taken off the secondary of the switcher.

I did some measurements from J1051 (the input to the 12 volt regulator to ground (the ground of C1051) it read 14.45 volts so thats fine.

A voltage measurement across the zener was 11.19 volts.

A measurement of the output of the 12V regulator when cold and when the deflection was not filling the screen by about 1/2 inch (across C1051) read 11.16 volts.

Unfortunately the zener diode isn't referenced in the parts section am I right in saying that it's a 12 volt zener? Hopefully a new zener will hold the supply closer to 12 volts when cold so I have full deflection when cold.

A slightly expanding deflection is just something I have to deal with due to the regulator design but at least I won't have to notice it with the screen filled out.

I also was thinking about scrapping the zener design and putting in a low dropout IC based VR. Is this worth it or should I just stick with a new zener?

All of this because the manufacturer was too cheap to derive the 12 volts off the switching transformer. I guess they saved money on that extra secondary huh ?

[Krankshaft]

Re: Panasonic PVC-2021 Vertical Deflection

Here is a pic of the zener and transistor.

I just checked the Rat shack's website and they have a IN4742A 12 volt 1 watt zener diode will this do?

[PlainBill]

Re: Panasonic PVC-2021 Vertical Deflection

Better look over the schematic again and trace the voltage levels. D1054 isn't a Zener; the Z is a notation.

Note that the 12V supply is switched. What happens to the 14 volt supply while this is happening?

PlainBill

[Wizard]

Re: Panasonic PVC-2021 Vertical Deflection

This is combination of switched and part of regulator in this circuit.

Pull up on base of Q1052 via on/off overriding the 11V zener and series of 2 diodes the regulator transistor (Q1051) cuts off due to grounded Q1052 transistor. Let it float free, the 30+ make sure to try to raise voltage higher on base of Q1051 but the outputs goes through a 11V zener (D1051) and series of two diodes to "raise" voltage drops (around .7V each for 1.4V appox plus 11V zener = 12.5V appox to take care of to drive the Q1052 in turn Q1051 transistor diode drops to give us near regulated 12V.

Quirky!! Check the feedback of PSU too, use ESR meter on all caps also. Use 11V zener. First: Heat up general area and careful aim with freeze spray tube right at the one component (I touch it with the tip of straw, in turn (press GENTLY on the sprayhead, freeze will seep and hiss slowly this way).

Cheers, Wizard

[Krankshaft]

Re: Panasonic PVC-2021 Vertical Deflection

Sorry about that I screwed up the diode designation I mean't D1051 the zener in front of the transistor in the photo.

Oddly enough D1052 and D1053 have been replaced with jumpers remind me to thank the beancounters.

I need to pick up another can of spray my current one was a bit low.

Anyhow the zener is right in front of the NPN transistor in the pic so it's hard to spray just it. However the odds of it being the transistor are alot less than it being the zener.

This little guy feeds both the vertical IC VCC (output 94) and the chroma IC (output 80).

It it a common occurrence for zeners to act this way?

[i4004]

Re: Panasonic PVC-2021 Vertical Deflection

>A slightly expanding deflection is just something I have to deal with due to the regulator design

wtf?
you just said panasonic tv has vertical breathing by design?
umh...

>This little guy feeds both the vertical IC VCC (output 94) and the chroma IC (output 80).

why are you making your life complicated?
you have scope, right? so check that voltage...
also check the datasheet of vertical ic...what if it can accept 10-12v os supply voltage?
then it means you're looking in wrong direction...

>it WAS in the PSU just like you said Wizard.

he told you to check the OTHER supply, the one behind the flyback...
he didn't told you to check main psu, just to be clear...

his first reaction was to replace the vertical ic, naturally...

>A measurement of the output of the 12V regulator when cold and when the deflection was not filling the screen by about 1/2 inch (across C1051) read 11.16 volts.

and when it's hot it's precisely 12V?

[PlainBill]

Re: Panasonic PVC-2021 Vertical Deflection

This is combination of switched and part of regulator in this circuit.

Pull up on base of Q1052 via on/off overriding the 11V zener and series of 2 diodes the regulator transistor (Q1051) cuts off due to grounded Q1052 transistor. Let it float free, the 30+ make sure to try to raise voltage higher on base of Q1051 but the outputs goes through a 11V zener (D1051) and series of two diodes to "raise" voltage drops (around .7V each for 1.4V appox plus 11V zener = 12.5V appox to take care of to drive the Q1052 in turn Q1051 transistor diode drops to give us near regulated 12V.

Quirky!! Check the feedback of PSU too, use ESR meter on all caps also. Use 11V zener. First: Heat up general area and careful aim with freeze spray tube right at the one component (I touch it with the tip of straw, in turn (press GENTLY on the sprayhead, freeze will seep and hiss slowly this way).

Cheers, Wizard

Yes, definitely a quirky circuit. It reminds me of the vacuum tube designs where it seemed every part performed two or more functions.

PlainBill

[Wizard]

Re: Panasonic PVC-2021 Vertical Deflection

i4004, not the flyback. The power supply and Krankshaft did find the problem there as well. That was good suggestion by me. Refrain from jumping on anyone please.

Cheers, Wizard

[370forlife]

Re: Panasonic PVC-2021 Vertical Deflection

Oh I almost forgot here are some pics of the vertical deflection when the set is cold and after it has warmed up.

Once when I ran it for an extended period it completely cleared up with no visible banding however when the set cools down again the process repeats itself.

He he, Harvey birdman.

[i4004]

Re: Panasonic PVC-2021 Vertical Deflection

>i4004, not the flyback. The power supply and Krankshaft did find the problem there as well. That was good suggestion by me. Refrain from jumping on anyone please.

i'm not jumping, or judging...but you said
"And go over supply caps that is near flyback transformer for the vertical B+ power."

and near the flyback there are some caps that filter the voltages that flyback supplies...so why would that point to main supply?
also, what is "vertical b+ power"?
i thought only flyback supply was named "b+"?

ie why not just write
"check psu output caps"

....and there he found no bad caps... <wink>

but yes, generally first thing to check is ICs supply...by measuring the voltage and scoping it to see if it has more ripple than it should have...

[PlainBill]

Re: Panasonic PVC-2021 Vertical Deflection

>
also, what is "vertical b+ power"?
i thought only flyback supply was named "b+"?

Nope. Now do you know why it's call B+ supply?

PlainBill

[Wizard]

Re: Panasonic PVC-2021 Vertical Deflection

B+ supply was old term in old days of tube. But the term stuck with us.

It meant power supply circuit or specific supply for specific item or two. Therefore:

We would refer as vertical B+ supply, or horizontal B+ supply.

It get bit wordy to say many things especially now that lot of stuff uses one PSU to have many different voltage supplies same with flyback transformer (which have about 5 outputs, even more: HV, focus, screen, vertical B+, 200V supply for cathode transistors blah blah.)

So, we just refer to check that vertical supplies, check such and such. So B+ term is slowly fading out.

In some RCA sets especially CTC195 onwards, it is no surprise to see about 15 to 30 supplies! Like octpus, Groan!

Cheers, Wizard

[Toasty]

Re: Panasonic PVC-2021 Vertical Deflection

>>...why it's call B+ supply?<<

That'll have 'em Googling for awhile...