Help needed on Philips set

[PortugalTV]

Hi to all
after the sucess of repairing the first of the four philips sets i bought last weekend, i started on the second one

contrary to the first, this one has a LOT of hours and is completely dirty with cigarrete crust


i got to a point where everything is working fine but i cannot get the vertical to lock
the picture either rolls up or rolls down as i turn the vertical stabilization potentiometer, i can make it roll fast or slow but not lock

so i started testing around the sync separator and the sync pulses for the vertical are present

i replaced a bunch of suspect capacitors around the vertical output and i replaced the vertical output tube
i took some readings with the oscilloscope and the vertical drive waveform is present and looking good but it seems to have low amplitude
from the oscillator to the output section the waveform looks inverted and weird, i included a picture showing it to you (i drawed it in blue)

the waverform frequency changes if i rotate the vertical hold (stabilization) control
i spent the entire afternoon testing and cannot find the problem

the components i highlighted in green were changed, the transistor was changed with an AC125(less current rating) temporarily but as it did not fix the problem i put back the original AC132

[Argus25]

You have described the fault as everything working fine but no vertical lock. But if the waveforms are grossly incorrect, for example a 40V vs 80v (but that "8" might be a 3) , your vertical scan would be about half the normal height and if the other waveform (in blue) was the wrong shape the scan linearity would be grossly abnormal.

So first, does the vertical scan look normal on the CRT or not ? (ignoring the lock issue) If it is ok, don't worry about your recorded waveforms vs what is in the manual, because they must be correct, regardless of what you have recorded.If the scan is reduced amplitude and distorted linearity this must be fixed first prior to the lock issue.

As for the vertical lock not working, can you post a copy of the sync separator part of the circuitry.

[PortugalTV]

hi argus
before anything else thank you very much for the input
ideed i cannot tell if that 8 is a 3..the scematic is low quality unfortunately but looking closely it may be 30v yes

you might be right i did not thought about linearity before, i was more worried to lock the picture and then i would fine-tune linearity height and all of that
this tv doesnt have a vertical hold knob accessible from the outside so it must have a way to self regulate ,it only has a trimmer potentiometer acessible by removing the back panel

when i said everything works fine i meant we have sound we have video we have high voltage we have horizontal and vertical deflection...

turning the vertical linearity potentiometer shifts the vertical frequency a bit but doesnt correct the linearity itself...the linearity is not correct.

about vertical scan or vertical deflection it fills the entire screen and its over stretched...reducing the vertical height doesnt correct the stretching.the image is always bigger than the screen and scanlines are very visible as a result. maybe a bad potentiometer...


i believe the sync separator is not the culprit because otherwise we would not see the drive waveform


here is the sync separator circuit, i think i labelled everything correctly



here is a video
https://www.youtube.com/watch?v=foqXGhrCkGM

it was recorded with the cellphone sorry for the bad quality

[Argus25]

Hi,

That clears it up. The thing to work on first is the abnormal drive waveshape to the vertical output valve. Check C221 and C107 and the resistors in the area.With that abnormality it is probable it might not sync with those abnormal waveshapes, so if you can fix this the V lock may come right .

Can you post a part of the schematic below the image in the post above and to the left of the diagram in the first post so I can see the circuitry there. Also, there might be some feedback from the vertical output transformer and yoke to part of the output valve's drive circuitry, can you include that, as if there is, the problem might be there.

[PortugalTV]

Hi Argus
thank you once again for spending your time to help
today unfortunately (or fortunately) i worked from 9:30am till now (23:15pm)

so i will check right now the capacitors you suggested and the resistors around the area now that i have a bit of spare time finally !!

meanwhile i uploaded the schematic for you to see
this forum does not allow big pictures so here it is

https://www.docdroid.net/pQtRqXi/x19...s-parecido.pdf
i think it will be easier for you to see the whole circuit instead of piece by piece right?

i will be right back to report my findings

[PortugalTV]

so today i tested all the components and connections marked on yellow
including removing the capacitors and testing for leakage...everything perfect
i tested the coils on the vertical output transformer that provide feedback, they measure about 250ohms so they are not open
the main primary and secondary i have not tested because if that was defective i would have no vertical deflection or it would be very limited...

while i was testing the tv, the boost capacitor decided to short...like it does on all philips tvs
so i replaced it temporarily (tacked a good old one on the back and cut the defective out), and after that i had to tweak a little bit the horizontal frequency coil in order to get the horizontal to sync again. so half hour wasted on that but thats fixed for now..I will replace it with a good mkp capacitor once i get the tv working well

so everything is like it was before
i will continue the search for the problem
next on the list is the voltage supply to the height potentiomenter r121, it goes through a couple of high value resistors
i will keep you informed

[Argus25]

I think you are on the right track, keep checking the components, especially ALL the electrolytic capacitors in the vertical circuits, they are the parts that are apt to go leaky, lose capacitance and or go high ESR.

[PortugalTV]

FINALLY SOME SUCESS

so after seeing the tv's block diagram i insisted on replacing again the "automatic raster stabilization transistor"
after replacing the transistor again with another one i had it is working!!!it locks horizontally and vertically
i still have to tweak a bit the horizontal frequency because it takes some seconds for the horizontal to lock

the picture is still too big and linearity is crap but i am relieved for now
i will do some resistor and voltage checks etc to correct those issues, i will also order some small electrolytic capacitors to replace the old ones.
now that it kind of works fine i can spend a bit of money in it , maybe disassemble and fully clean the cabinet etc
i will keep you updated