Panasonic PVC-2021 Vertical Deflection

[Wizard]

Re: Panasonic PVC-2021 Vertical Deflection

They will find out easily enough.

Hint, it is about old days of tubes where this term came from.

Cheers, Wizard

[PlainBill]

Re: Panasonic PVC-2021 Vertical Deflection

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

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

And a couple more: What was the A supply used for? And the C supply? (OK, that last was from before my time).

PlainBill

[i4004]

Re: Panasonic PVC-2021 Vertical Deflection

>We would refer as vertical B+ supply

well, YOU would, but most of the world wouldn't these days.
<wink>

i know where "b+" comes from, worry not, but did any of you saw "b+" feeding the vertical IC?
got it?

in tv, b+ goes to flyback and is switched by flyback transistor...it's usually the highest voltage from main psu...

>PSU to have many different voltage supplies same with flyback transformer (which have about 5 outputs, even more: HV, focus, screen, vertical B+,

oh...you just admitted you infact were reffering to flyback output supply when you said it above...
good, good, good...
<wink>

[Wizard]

Re: Panasonic PVC-2021 Vertical Deflection

>We would refer as vertical B+ supply

well, YOU would, but most of the world wouldn't these days.
<wink>

i know where "b+" comes from, worry not, but did any of you saw "b+" feeding the vertical IC?
got it?

in tv, b+ goes to flyback and is switched by flyback transistor...it's usually the highest voltage from main psu...

>PSU to have many different voltage supplies same with flyback transformer (which have about 5 outputs, even more: HV, focus, screen, vertical B+,

oh...you just admitted you infact were reffering to flyback output supply when you said it above...
good, good, good...
<wink>

Twisting words again, some models use power supply outputs to supply power to vertical too like I said before for Krankshaft's case. Commonly done in monitors. In TVs but usually use the 24V to 26V from flybacks for vertical's power but some did get it's power from power supply instead.
B+ is just a name that can apply to any kind of power sources. B+ had specific meaning back in tube days but it lost it's specific meaning when transistor came along (no need for specific tube voltage now) but useage is carried on by habit by some techs and *very occasionally* one see a "B+" in schematic. Modern convention in schematics follows thus: Some use unique voltage and highlighted in one color, most don't, just plain voltage in cheap schematic and some very detailed schematics had a name for voltage with suffixes to denote specific areas:

5Vsba, 5Vsbb especially if it is tapped from 5Vsba via a fusible resistor, diode or a fuse even just a jumper (!), 15V_Vertical, 20V_protect, 33V_Tuner so on. I can show examples from RCA and JVC schematics of this particular thing.

life is interesting so take it as you go instead of twisting one's words as a game. People don't appreciate that at all in that manner.

Cheers, Wizard

[Krankshaft]

Re: Panasonic PVC-2021 Vertical Deflection

And a couple more: What was the A supply used for? And the C supply? (OK, that last was from before my time).

PlainBill

The A supply was the filament supply in portable tube radios the B battery was for the plates and the C was for grid biasing before it was phased out and taken over by the B.

I wanted to figure out where that term came from I was working in tube equipment ahwhile back.

The screen fills out at about 11.45 volts when heated. That's the output from the regulator I'll check the supply at the vertical VCC pin directly later tonight.

The circuit uses an LA7837 the recommended voltage on VCC pin 1 on the datasheet is 12 volts.

Do all Panasonics have quirky circuits like this or am I just on a roll?

[Toasty]

Re: Panasonic PVC-2021 Vertical Deflection

Panasonics have been quirky since I remember. Going way back to the "modular" days. Vertical circuit was an issue back then too.

Toast

[Krankshaft]

Re: Panasonic PVC-2021 Vertical Deflection

For the heck of it I'm going voltage probing before I pickup another zener since this will be a special order anyways.

Luckily they provided a voltages chart for this TV too.

[Toasty]

Re: Panasonic PVC-2021 Vertical Deflection

B+ was from the batteries for the plates, yes. But, it was a high voltage up to 90 vdc. B batteries that I recall seeing were 45, 63, and 90 volts. A real eye opener if you came across them unsuspectingly.

In my "untrained" years, I had strung some 9 volts together to get what I needed for an old set I was toying with. Forgot what voltage I had there and WHEEEEEE!!!

I looked like the cat for a minute.

Toast

[Krankshaft]

Re: Panasonic PVC-2021 Vertical Deflection

I remember when I was 14 and tried removing the anode lead from a 13" CRT without discharging it doesn't get much stupider than that . I hurled that screwdriver across the room luckily noone was behind me.

Luckily now I use an isolation transformer and am more concious about electrical safety.

According to the voltage chart IC451 (the vertical IC) pin one should be 11.4 volts. At cold it was 11.19 the vertical wasn't filled after about 10 minutes of warmup it filled up and the voltage was 11.44.

I'll pick up a new zener and replace it and see what happens.

[PlainBill]

Re: Panasonic PVC-2021 Vertical Deflection

I remember when I was 14 and tried removing the anode lead from a 13" CRT without discharging it doesn't get much stupider than that . I hurled that screwdriver across the room luckily noone was behind me.

Luckily now I use an isolation transformer and am more concious about electrical safety.

According to the voltage chart IC451 (the vertical IC) pin one should be 11.4 volts. At cold it was 11.19 the vertical wasn't filled after about 10 minutes of warmup it filled up and the voltage was 11.44.

I'll pick up a new zener and replace it and see what happens.

There may be more going on here. A quick Google refreshed my memory. An 11 Volt Zener has a positive temperature coefficient. The two diodes in series may be there to compensate for that.

Another thought, very precise zener values are possible, but they are uncommon. 5% and 10% tolerance is more typical. You are seeing a 3% voltage change as it warms up. This is well within the normal variation you would expect to see between different sets. Now it IS possible that the diodes were selected to provide a precise voltage, but that doesn't make sense in consumer electronics. MA4110N-HTA does appear to be a common Panasonic part.

I wonder if you aren't seeing a combination of problems here. According to lower left corner of the first schematic you posted, there is a vertical height adjustment on the main board.

But what do I know?

EDIT:

PlainBill

[Krankshaft]

Re: Panasonic PVC-2021 Vertical Deflection

That's the kicker those two diodes were removed and replaced with jumpers thanks to the bean counters.

I considered adjusting the V Height but that is controlled by the microcontroller if it was fine at the factory it doesn't make sense for it to need adjustment now. That line goes to the deflection IC.

I don't have the remote for this TV it's a PITA I can get into service mode from the front panel find V Height but can't adjust the value without pressing the channel button (on the remote) my universal won't work with it either. It never ends.

I am thinking if using a slightly higher voltage diode like 11.5 avg vs a 11.0 one.

[Wizard]

Re: Panasonic PVC-2021 Vertical Deflection

Add another diode and see on that beancounter's jumper?

Finish recapping the supply btw?

Cheers, Wizard

[PlainBill]

Re: Panasonic PVC-2021 Vertical Deflection

Add another diode and see on that beancounter's jumper?

Finish recapping the supply btw?

Cheers, Wizard

Ohhh!!! I like that idea!! That should jump the voltage up enough to give a full screen AND provide thermal compensation.

PlainBill

[Krankshaft]

Re: Panasonic PVC-2021 Vertical Deflection

Yes I replaced all of the caps just in case.

I can add a diode the parts list doesn't list a part number for D1052 will a standard rectifier diode do like an IN4007?

[PlainBill]

Re: Panasonic PVC-2021 Vertical Deflection

Yes I replaced all of the caps just in case.

I can add a diode the parts list doesn't list a part number for D1052 will a standard rectifier diode do like an IN4007?

Look at the schematic. The main pass transistor is Q1051. It's in a voltage follower (common collector) configuration, and the base is pulled high by the parallel resistors R1052 and R1053 to +30 volts. The two resistors are handling a maximum of 4 ma. Q1052 regulates by pulling the base of Q1051 down, so it will have to sink a maximum of 4 ma; 2.4 ma when regulating. Q1052, requires less than 1 ma (probably less than 100 µa) of base current. R1051 is the only other load, it will be carrying about 600 µa. I'd say use a 1N4148 or other low current diode.

Unless my calculations are way off, the problem may be due to the fact that D1051 isn't in it's stable range.

PlainBill

[Toasty]

Re: Panasonic PVC-2021 Vertical Deflection

nm

[Krankshaft]

Re: Panasonic PVC-2021 Vertical Deflection

Well while I don't have any IN4148s I do have an NTE 519 a cross reference for an IN4148 I'll install it later and check the VCC when cold.

[Krankshaft]

Re: Panasonic PVC-2021 Vertical Deflection

Success!!!

Thanks for the help again the NTE519 was just a part number the diode was a real IN4148.

Usually NTE recodes their parts but this one wasn't recoded.

Upon installing it at cold the VCC at pin 1 was at 11.82 the vertical was filled out when it warmed up it rose to 11.96 and stayed there rock steady without faltering.

I'm willing to say it probably has been like this since the factory during calibration the TV probably had been warmed up when the V height was adjusted.

I guess this just proves if you contantly keep axing parts from the original design stuff like this is bound to happen.

[PlainBill]

Re: Panasonic PVC-2021 Vertical Deflection

Success!!!

Thanks for the help again the NTE519 was just a part number the diode was a real IN4148.

Usually NTE recodes their parts but this one wasn't recoded.

Upon installing it at cold the VCC at pin 1 was at 11.82 the vertical was filled out when it warmed up it rose to 11.96 and stayed there rock steady without faltering.

I'm willing to say it probably has been like this since the factory during calibration the TV probably had been warmed up when the V height was adjusted.

I guess this just proves if you contantly keep axing parts from the original design stuff like this is bound to happen.

Congratulations on getting it working.

It's time someone corrects a misconception. In any properly run operation 'bean counters' are NOT allowed to eliminate parts from a design to save money. How much money do you think Panasonic would save by removing one 1N4148 from every set? I'll give you a hint: Depending on manufacturer, DigiKey will sell a reel of 10,000 1N4148s for as little as $0.0027 each - yeah, 1/4 cent!! Those diodes were a provision so a tech at board test could quickly and easily set the power supply voltage without using a pot that some diddle stick jockey could twist 'to see if that helps'. Note that vertical height adjustment was available, all it required was a remote control!!!

When I worked in manufacturing, some of our products came of the assembly line with as little as 1/3 of the possible components installed. One particular card was a 16 channel digital input card. Various options included 5, 12, and 24, VDC input with or without filtering, and with or without optical isolation. The 5VDC unfiltered, non-isolated card had about a dozen chips, the rest of the card had a couple of dozen jumpers. The caps, resistors, and opto-isolators weren't skipped to save money, the were omitted because the application didn't use them. We saved because we could build 12 different products on the same circuit board.

PlainBill

[i4004]

Re: Panasonic PVC-2021 Vertical Deflection

>life is interesting so take it as you go instead of twisting one's words as a game. People don't appreciate that at all in that manner.

i wasn't twisting anything, really. it is what you said, and later confirmed, as i showed.
so why blame me if you told him to check supply of vertical that comes from flyback, by your account...

i've found it peculiar as i've never seen it, ie never seen vertical ic supplied by flyback...flyback usually supplies crt voltages etc.
not saying it's impossible, but i doubt it's done in any recent tv...

i mean, heck i was just looking at electric diagram for b/w tv with a linear supply and vertical chip is supplies from it, not the fylback circuit...

perhaps it was more usual in usa than in europe, dunno....

> can show examples from RCA and JVC schematics of this particular thing.

can you show shematics showing vertical ic supplied by flyback?
what make/model and year?

-----------------
>Do all Panasonics have quirky circuits like this or am I just on a roll?

well, you're fixing them, who said it must be easy?
<wink>
and one learns most from quirky problems anyway.

>According to the voltage chart IC451 (the vertical IC) pin one should be 11.4 volts. At cold it was 11.19 the vertical wasn't filled after about 10 minutes of warmup it filled up and the voltage was 11.44.

interesting that such a small change makes a big difference....but yeah, from vertical ic datasheet it was obvious it requires particular voltage, as there's also 9v circuit version(same ic, but 9V supply) that's different etc.

>Those diodes were a provision so a tech at board test could quickly and easily set the power supply voltage without using a pot

so one would expect some tvs of this model to have diode(s), and others not to have it?

i really dunno why they bothered...why not just put 7812 and be done with it...

this is pretty sloppy, but panasonic (probably just like everybody else) got sloppier when prices needed to fall down(in order to be able to sell anything at all)...
pitty....
but older models should be better in that aspect...