Sony KP-53V85 extremely bright picture and then shut down

[Guest]

I've got a friend that recently acquired this tv for free (due to this same problem).

Upon initial power up, the picture is very bright (like the brightness is cranked all the way up). However, adjusting the brightness makes no change. After awhile the tv will turn off. Maybe some type of protection circuit? Is there any kind of diagnostic feature with this set?

I'm obviously not a tv tech but I'm familiar with electronic components (can do some minor component level trouble-shooting) and know that tv's should be treated with great respect...

Any help would be greatly appreciated!

Thanks!
Joe

[torbjorn]

In general, a common cause for too high brightness is that the voltage on the CRT's screen grid (VG2) is too high for some reason. Normally, it is taken out from the focus tap on the high voltage transformer via a voltage divider which is often integrated in the transformer. One of the pots on the transformer is for adjusting the screen grid voltage. On some japanese televisions, the resistor from the negative terminal of the screen grid pot to ground is outside of the transformer and often fails open circuit.
The VG2 is usually between 500 and 800 V, i.e. too high to be comfortably measured by a cheap DMM. The best way of checking this is to check if the brightness varies when you adjust the pot. Also, if you have possibility to measure high resistances (tens of megohms), then you could try measuring the voltage divider.

Another possibility is that the supply voltage for the video output stages (usually about 200 V) is too low.

[minnie]

Try turning down the screen control.

[cory]

i think it was this model,can someone confirm,need to replace 3 spark gaps and three transistors on crt pcbs. one of eack on each board.does menu appear or you cant see it? with this problem you cant see on screen menu.