Flyback Transformer Shot?


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Flyback Transformer Shot?

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Trespasser
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Jun 26, 2009, 3:24 AM

Post #1 of 19 (553 views)
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Flyback Transformer Shot?	Can't Post

Hi,

I'm trying to fix an old Loewe TV. I replaced a fuse, but now I get a corona discharge across the top of the flyback transformer where it shouldn't be.

Any experienced opinions of how to proceed? Could I just need a new flyback transformer?

Tressie.

jts1957
Veteran

Jun 26, 2009, 9:11 AM

Post #2 of 19 (551 views)
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Re: [Trespasser] Flyback Transformer Shot? [In reply to]	Can't Post

Time to play: Let's All Try To Guess The Model Number?

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techchris
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Jun 26, 2009, 4:47 PM

Post #3 of 19 (544 views)
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Re: [Trespasser] Flyback Transformer Shot? [In reply to]	Can't Post

if an arc comes out of the transformer then the insulation has broken down and the transformer needs to be replaced before any other damage occurs from all the arcing and sparking

Trespasser
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Jun 27, 2009, 12:07 AM

Post #4 of 19 (539 views)
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Re: [techchris] Flyback Transformer Shot? [In reply to]	Can't Post

Hi techchris,

Thanks for the input as regards my flyback transformer.

What are my chances of finding a compatible replacement transformer in similarly sized, dumpster retrieved colour TVs? Are they all different, or are there specific designs common to various sets?

Tressie.

techchris
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Jun 27, 2009, 2:19 AM

Post #5 of 19 (536 views)
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Re: [Trespasser] Flyback Transformer Shot? [In reply to]	Can't Post

they are model and make specific, so buy a new one from a spares supplier they are not that expensive

Trespasser
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Jun 28, 2009, 11:34 PM

Post #6 of 19 (518 views)
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Re: [techchris] Flyback Transformer Shot? [In reply to]	Can't Post

Okay, I cleaned the dust off the flyback transformer. I can still hear some minor arcing emanating from it, but at least I get a picture. I'll replace the FBT if my next problem isn't too serious.

Yesterday, I got a pretty good picture. I spent the day figuring out that the speakers needed an external loopback, so now I have sound also. Today when I turned it on, I got a bright green screen. You can see scan return lines across the screen, and the picture is there in the background. After jiggling a few plugs etc., I got an almost white screen, with the scan return lines and image superimposed. After a few seconds of this the TV turns itself off.

Can anyone please help me to understand why I now have the ultra-bright screen, and whether it might be in some way related to the dodgy FBT?

Regards,
Tressie.

techchris
Veteran

Jun 29, 2009, 5:40 AM

Post #7 of 19 (511 views)
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Re: [Trespasser] Flyback Transformer Shot? [In reply to]	Can't Post

the lower control on the transformer needs to be turned anticlockwise slightly. it sounds like the screen volts are set too high. Its not wise to run the tv with high voltage sizzling around the transformer as it can do serious damage to other components

jts1957
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Jun 29, 2009, 10:03 AM

Post #8 of 19 (508 views)
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Re: [Trespasser] Flyback Transformer Shot? [In reply to]	Can't Post

Some of the technicians (and others here) have access to their own records and other sites that have repair tips, etc.
It's hard to obtain a small number of results with No or little specific information. (Google "Loewe Tv" = 464,000 hits / Loewe Compose TV = 54,500 hits).

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Trespasser
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Jun 29, 2009, 7:46 PM

Post #9 of 19 (502 views)
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Re: [techchris] Flyback Transformer Shot? [In reply to]	Can't Post

Hi Techchris,

I managed to patch-up the broken-down insulation at the top of the FBT with some 5-minute epoxy. It doesn't arc anymore.

I got a good picture by fiddling with the on-screen contrast adjustment and the screen volts pot on the FBT. It worked superbly all evening. Then when I turned it on again this morning, the picture slowly became bright green again. Now I have just the bright green screen with scan return lines. If you leave it to cool down for a minute or two, then you get some picture back, but then it washes out again. Maybe I should try to isolate this with some freon?

Regards,
Tressie.

jts1957
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Jun 29, 2009, 7:54 PM

Post #10 of 19 (501 views)
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Re: [Trespasser] Flyback Transformer Shot? [In reply to]	Can't Post

Screen volts NOW too high. Wink

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Trespasser
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Jun 29, 2009, 9:34 PM

Post #11 of 19 (497 views)
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Re: [jts1957] Flyback Transformer Shot? [In reply to]	Can't Post

Hi jts1957,

Sorry, it's a Loewe ERGO 6572 zp.

I openned it up again and tried to adjust the screen voltage pot on the side of the FBT once more. It makes some difference to the underlying picture, but the bright green screen with scan return lines remains. Gee, the picture was superb last night. I can't think what's happened to change that.

Oh darn, it looks like I might need $chematics after all.

Regards,
Tressie.

Trespasser
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Jun 30, 2009, 1:56 AM

Post #12 of 19 (490 views)
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Re: [Trespasser] Flyback Transformer Shot? [In reply to]	Can't Post

Hmm...this is odd. I measured the voltage at the FBT transformers screen voltage adjustment tap output. The wire goes to the picture tube neck pcb, and measures a consistent 130V. Curiously, it doesn't change as the picture goes from normal, to warmed-up with a bright green screen.

What other voltages being supplied to the CRT could I check for the variation, I wonder?

Regards,
Tressie.

FUXER
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Jun 30, 2009, 3:39 AM

Post #13 of 19 (488 views)
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Re: [Trespasser] Flyback Transformer Shot? [In reply to]	Can't Post

Pic tube showing classic signs of green gun cathode/heater short- ways to overcome- 1 of is isolate heater input & run 3 turns around lopt limb in lieu to heater- other ways involve clearing short & may have risk. Angelic

jts1957
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Jun 30, 2009, 8:16 AM

Post #14 of 19 (481 views)
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Re: [Trespasser] Flyback Transformer Shot? [In reply to]	Can't Post

Replace the transformer already! Crazy

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Trespasser
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Jun 30, 2009, 11:15 PM

Post #15 of 19 (469 views)
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Re: [jts1957] Flyback Transformer Shot? [In reply to]	Can't Post

Hi jts1957,

Hmm...I wasted a can of freon cooling down everything on the neck pcb and chassis. The only thing that seemed remotely sensitive to the cooling was the FBT. It began to arc a little, and my screen went from green to grey, but was still way too bright.

Flyback transformers will be scarce and expensive where I live. I wonder if someone could suggest an inexpensive source on the web?

Regards,
Tressie.

jts1957
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Jul 1, 2009, 6:58 AM

Post #16 of 19 (462 views)
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Re: [Trespasser] Flyback Transformer Shot? [In reply to]	Can't Post

Any "Location" number?
How about numbers on the transformer itself?

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rrobor
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Jul 3, 2009, 3:27 AM

Post #17 of 19 (447 views)
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Re: [jts1957] Flyback Transformer Shot? [In reply to]	Can't Post

Fuxer gave you your fix, its a short in the tube, I think his advice was 3 turns, I think it should be 2.

FUXER
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Jul 3, 2009, 3:55 AM

Post #18 of 19 (446 views)
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Re: [rrobor] Flyback Transformer Shot? [In reply to]	Can't Post

It depends on the pic given- if a little dull I experiment with turns- a true rms meter should measure 6v3 ac- another guide is colour of heater- should be dull orange- recall 1 set(Rank Arena C26xxx) where 3&1/2 turns needed. Really depends on intrinsic voltage in lopt(modern sets run eht 30kv or so- early sets had 25kv max- bearing in mind x-rays produced over 27.5kv!. Unimpressed

rrobor
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Jul 4, 2009, 5:17 AM

Post #19 of 19 (433 views)
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Re: [FUXER] Flyback Transformer Shot? [In reply to]	Can't Post

I tend to start at 2 turns, that usually gives about 6,3. If its dull, yes I go for the 3 turms and resistor it down. But I am here and you are there and Ive never fixed there so perhaps we are both correct. Used to have a Rank Arena C2601, pin I could never get quite right and as it was my own, didnt bother that much.

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