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Equipment Repairs => CRT TV forum => Topic started by: Turnip on January 20, 2010,11:36:57

Title: Panasonic TX28PB50 Euro 7
Post by: Turnip on January 20, 2010,11:36:57

Hi folks,
Have one of these where at switch on, PS pulses for perhaps 10 seconds then cuts. Thought to check LOP collector which shows little initial voltage, but resistance wise (Avo 8 of course), it's 12 Ohms one way and 100 Ohms the other. Suspect 100 Ohms is too high for a PS secondary diode short - any thoughts ?  - Chris.

Title: Re: Panasonic TX28PB50 Euro 7
Post by: Contrast John on January 20, 2010,12:24:24

Hi Chris
Assume you mean 100 ohms to deck. Probably a leaky line output transistor. Usually caused by dry joints in line stage or high HT from the psu.
Regards
John.

Title: Re: Panasonic TX28PB50 Euro 7
Post by: sparky on January 20, 2010,12:57:21

hi
in that model line-out
 transister as internal diode
best to measure out of circuit
check line drive transformer pins become
dry can see with magnifier
sparky

Title: Re: Panasonic TX28PB50 Euro 7
Post by: Turnip on January 22, 2010,08:00:18

Hi, and thanks,

Checked LOP, found it leaky. Replaced checking for dries esp around L/drive tx. Plugged in and sound came up with picture rather narrow E/W with some foldover. LOP then died. Suspect I have a duff LOPT to replace - Chris.

Original LOP is 2SC5591 (non integral diode) I replaced with BU4508AX, nearest I had.
Checked ChasHyde, tranny some £75 ish - ah well.

Title: Re: Panasonic TX28PB50 Euro 7
Post by: brainstorm on January 28, 2010,05:51:53

Hi,

If line op transistor is leaky then always check for drys on line driver transformer on panasonics,
and check yout HT hasnt gone high. but you are probably right that its the Line op transformer

Brian

Title: Re: Panasonic TX28PB50 Euro 7
Post by: Turnip on January 28, 2010,13:16:49

Hello, and thanks Brian,

Had the thought that with a Panasonic, dries in the line drive area might be the problem, but foldover after resoldering and demise of replacement LOP suggested an excessive load.

One more for China, lets hope it comes back as an LCD - Chris.

Title: Re: Panasonic TX28PB50 Euro 7
Post by: tv john on January 30, 2010,17:11:31

Do you not have to use the origional o/p tr for that chassis ?

John.

Title: Re: Panasonic TX28PB50 Euro 7
Post by: Turnip on January 31, 2010,05:14:11

Hi and thanks John,

You may well be right. Have in the past had trouble with Sony FE2 in particular where similar'ish LOPs got hot after a short while, but generally checking specs first gets me out of trouble with minimum stock.

Like most repair folks I have a quantity of semiconductors salvaged from scrap and am reluctant to spend possible profit for even more that might just sit on the shelf - especially these days.

Thanks again - Chris.