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Panasonic TX28PB50 Euro 7

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Turnip:
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.

Contrast John:
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.

sparky:
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

Turnip:
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.

brainstorm:
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

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