Panasonic tv help...

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dacflyer
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Panasonic tv help...

Post by dacflyer »

i have a panasonic CT-27D32F chassis QP338
you turn it on and a second later it shuts down, HV shut down.i think,
i checked the B+ is ok, i have the schematic, but theres no troubleshooting help in it at all..
anyone have a clue ?
not much help on the net either.
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Janitor Tzap
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Re: Panasonic tv help...

Post by Janitor Tzap »

You do get the interesting ones don't you. :wink:

This site has the service manual for $10.
http://www.electronicsrepair.net/television6_ct.shtml

Was this a Lightning, or Voltage Surge victim?

The thing is....
Once you get the set to at least power on.
You may find that the Jungle Chip, Tuner, or Processor has been fried.

Have you tried to bring the voltage up slowly with a variac?
You may get it to power on at a lower voltage, say 80Vac - 100Vac.
Long enough to see if there are other problems.

Other than that, start looking for bulging or popped electrolytic capacitors.
Or more likely, look at the board around were the capacitors are mounted.
I've been finding some caps that the seal has failed, and the oil leaks out the bottom.


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dacflyer
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Re: Panasonic tv help...

Post by dacflyer »

i have the service manual. several versions :P servicemanuals.net
the set is not victom to lightning or surge. this set was in use with a bank of 12 tv's all identical
if i dissconnect the collector of the H.O.T. the sets power supply will power up, and i get the normal B+ so i am suspecting it is something in the secondarys of the flyback.
i may just dissconnect the flyback 1 pin at a time. and test each pin.

just thought there was some troubleshooting info out there, like sams used to show..
the manuals i have show no T.S. help.
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Janitor Tzap
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Re: Panasonic tv help...

Post by Janitor Tzap »

Ok,

I didn't realize you had a schematic to use. :?

Well, find the High Voltage Protect Circuit, or X-Ray Protect Circuit.
Check the Zener diodes, or High Voltage Shockley diode.{I think that's right.}
And see if they are shorted or open.
{And look for bad high voltage capacitors in those sections.}
Check the FlyBack Transformer.{Look for cracks}
It may have an open winding in one of the secondaries .

While your at it......
Slap a CRT tester on the jug, and see if it has any problems as well.
It would be a shame to spend a whole lot of time on this set.
Only to find out that the jug has a grid short, or one of the guns has shorted to the heater.

Good luck.


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dacflyer
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Re: Panasonic tv help...

Post by dacflyer »

HOT HOT HOT !
ok, i think i found the problem. even tho my B+ is normal at least until it goes into shutdown.
i did crank the power down with variac. bout 85 volts is all it would handle before going into shutdown. i let the set power up, i could hear it..but i get no raster or filiment glow. after about 5 min of running and testing. i started to hear something different.. the flyback started making a growling noise, and in unison the PS also started to make same noises.lowered the power further, tested again.this time it was all the time...i shut the set down. started feeling around for heat.. the flyback was hot as hell. the H.O.T. heatsink was warm, i think i am almost sure that the flyback is bad, cause i am not getting any voltages out of it..and the HV anode has weak output. barely can get a 1/4" spark. if it was good, i should have been able to draw almost a 2" spark..
well PAUSE for now til i order a new flyback..

usually when a FBT went bad on me, they just went out totally.
stay tuned :P
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Re: Panasonic tv help...

Post by Ken1 »

Hi, Your flyback is definitely bad. At 85V you should have a decent picture with some shrinking from all 4 sides and reduced brightness; otherwise normal. I have troubleshooted many sets with suspect bad flybacks with a variac and have always gotten a picture at 80V if the flyback was good. Before installing the new flyback I highly recommend that you check all the diodes, capacitors, etc on all the outputs of the flyback to make sure there are no shorted components that overloaded the flyback and caused it to overheat and fail in the first place.
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Janitor Tzap
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Re: Panasonic tv help...

Post by Janitor Tzap »

Oh...
I've seen a lot of flybacks fail like this. :lol:

Well, at least you now know what is the major cause of the problem.

But, check your schematic, and see if the Heater Voltage for the CRT comes from one of the secondary windings of the Flyback Transformer.
If it does, check the CRT and make sure it is good!
You don't want to end up buying parts unnecessarily, if the tube is shot.

I've seen cases where as the CRT ages.
The Heater Voltage current will climb, as will the 180Vdc grid voltages.
This puts a strain on the Flyback, and can cause it to over heat, and a windings to open up.
Or it melts the insulation material in side it, shorting the windings.

If the CRT is fine.

Ken1 is right,
in that you should check the components coming off the secondary windings of the Flyback.
To make sure that they are ok.


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Lenp
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Simple Coil Ring Test!

Post by Lenp »

Years ago when I was in the consumer repair business we modified a scope by taking a pulse from the sweep circuit output with a capacitor, maybe .1uf or so, and connected it back to the vertical input. If you put an inductor between that point and ground, and adjusted the vert gain and sweep speed, you could get the coil to 'ring'. A good coil will have many decaying oscillatons, a coil with a shorted turn will have a severely damped trace, maybe a part or 2 oscillations after the pulse. A litttle experience and you can quickly spot a shorted flyback, yoke or power transformer. Usually any turn shorted on a multi-winding inductor would dampen the ringing. Also if there are any capacitors across the windings try the ring test and if it doesn't look right, disconnect the caps to be sure they aren't doing the dampening. We simpy used a jack for the pulse and a special set of leads made just for the purpose. As simple as it is, it sure saved the day in many cases.

Len
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"I must be on the way to success since I already have the junk". (Me)
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dacflyer
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Re: Panasonic tv help...

Post by dacflyer »

Janitor Tzap > i am sure its the flyback, i have disconnected all the secondarys and also unplugged the tube, all that was connected was the 2 connections on the flyback to power it.
(primarys) so i am sure of it. the set is not that old anyway.
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Janitor Tzap
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Re: Panasonic tv help...

Post by Janitor Tzap »

Lenp wrote:Years ago when I was in the consumer repair business we modified a scope by taking a pulse from the sweep circuit output with a capacitor, maybe .1uf or so, and connected it back to the vertical input. If you put an inductor between that point and ground, and adjusted the vert gain and sweep speed, you could get the coil to 'ring'. A good coil will have many decaying oscillatons, a coil with a shorted turn will have a severely damped trace, maybe a part or 2 oscillations after the pulse. A litttle experience and you can quickly spot a shorted flyback, yoke or power transformer. Usually any turn shorted on a multi-winding inductor would dampen the ringing. Also if there are any capacitors across the windings try the ring test and if it doesn't look right, disconnect the caps to be sure they aren't doing the dampening. We simpy used a jack for the pulse and a special set of leads made just for the purpose. As simple as it is, it sure saved the day in many cases.

Len
:lol: So, you made a Yoke/Flyback Tester. :lol:
I've got one of Heathkits IT-5235 testers.
I don't use it that much.
Because most coil or inductor failures are fairly easy to spot, with out having to do a ring test.
dacflyer wrote:Janitor Tzap > i am sure its the flyback, i have disconnected all the secondarys and also unplugged the tube, all that was connected was the 2 connections on the flyback to power it.
(primarys) so i am sure of it. the set is not that old anyway.
Ok, :roll:

But after what you told me about this set being one of twelve sets.
I get the impression that this set has been running 24/7 since it was new.
The set may not be physically old.
But, it has a lot of running hours on it.


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haklesup
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Re: Panasonic tv help...

Post by haklesup »

Surely you're right about the flyback being bad but I think the others were concerned about the "Chicken or the Egg" effect in that did the FB fail alone or did something cause it.
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Re: Panasonic tv help...

Post by dacflyer »

the set get about 8hrs a day use, so ya its got some age on it.. we turn them off after work, they are all on timers which is cool, and they turn on automatically also.. nice tv feature.

i belive the FBT just failed from age. cannot find anything else wrong. everything else cheaks out ok.. something has to fail sometime..:P
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