Hi TV friends
my Philips 21 leonardo volautomatic TV has started getting a very dark picture lately !
in the past , the tv was all repaired by me, new electrolitic capacitors and general maintenance and it worked very well for the last months!
now the sound is good, but the picture is very very dark
without a signal on the antenna, the regelspannung (AGC) voltage is -1,5volts and if i inject composite video on the grid of the video verstarker the tv displays the video
but the moment i touch a signal to the antenna input, the regelspannung jumps to -50 sometimes -90volts and the picture gets very very dark
i have been testing components for 10 hours now and i even replaced all the Rohren by new ones that i have here.
there is a VDR that does the regulation of the regelspannung (R63), i tried disconnecting it and short circuiting it, both with no effect
i really dont know what else to test
i will be very gratefull if you loose some time helping me. i have an oscilloscope and multimeter as test tools
my video source is working well because i tested it on other tv's
the circuit around the contrast and brightness control has been checked, i really know that this is a problem with regelspannung regulation
this is signal through the antenna
Dateianhang:
WP_20190414_17_00_46_Pro.jpg [ 124.99 KiB | 9985-mal betrachtet ]
this is video injected on the grid of the video verstarker
Dateianhang:
WP_20190414_17_01_05_Pro 1.jpg [ 109.9 KiB | 9985-mal betrachtet ]
i uploaded the schematic to here
https://www.docdroid.net/fDYfmZg/21td310a.pdf#page=5