Italian 1962 TV B&W

[lucvic]

Hi dear all,
I'm writing from Italy ( my english is not so good),
I started to try repairing this set 20 days ago.
I changed all electrolitics caps but vertical sync is
unstable (I need to adjust vert freq pot if I change image pattern).
No focus on sound yet.
I can share here the schematics if someone will so polite to help me
to understand how this set works.

thank you

best regards
Luca

[kvflyer]

Hello Luca. Welcome to the VideoKarma forum. I can't add any help but I am sure there are many here that will be willing to help. Good luck and you must know that we like pictures.

[lucvic]

here's the schematics

thank you

[Sandy G]

Nice to have you ! Welcome !

[init4fun]

Originally Posted by lucvic

here's the schematics

thank you

Hi Luca ,

I had a quick look at your schematic and if this were mine to troubleshoot I'd start taking voltage measurements at the video detector diode and go on taking measurements through the sync separator and then on to the vertical deflection circuits and compare them to the values listed on your schematic . The place where you find voltage that does not conform to the schematic will be in the general area of the trouble .

Just curious , do you have an oscilloscope ?

[lucvic]

thank you,

yes I have a digital scope,

the signal on the grid of 15tp7 seems ok (pin 8)
I don't understand why there is a pulse superimposed probably coming from
horizontal transf to the video signal. automatic frequency control works properly so this pulse doesn't affect the image.

[Sandy G]

Your English is a LOT better than my Italian...About the only Italian I know is names of cars..."Maserati Bora, Ferrari Tessarosa.." (grin)

[init4fun]

Originally Posted by lucvic

thank you,

yes I have a digital scope,

the signal on the grid of 15tp7 seems ok (pin 8)
I don't understand why there is a pulse superimposed probably coming from
horizontal transf to the video signal. automatic frequency control works properly so this pulse doesn't affect the image.

Could you possibly post a photo of your scope displaying the waveform at TP9 , In the area of the 12ET1 Sync separator ?

[wa2ise]

Originally Posted by lucvic

I don't understand why there is a pulse superimposed probably coming from
horizontal transf to the video signal. automatic frequency control works properly so this pulse doesn't affect the image.

Sometimes the clip lead on the scope probe will pick up some of the horizontal flyback pulse, via magnetic coupling. And cause this waveform to get added in the scope to the real waveform you're trying to probe. Try repositioning this clip lead, also the path the scope probe lead wire could also pick up some horizontal, so try to route this away from the flyback transformer area.

[lucvic]

Hi,
in last week end no time to work on this,
but this evening I found two things:

1) R557 increased from 5.6Meg to 27Meg ( tomorrow I will change)
2) someone in the past changed C549 (cathode of final video amplifier)
from 470pF to 100uF. I don't have one, I put a 1nF but the contrast in the
screen is very reduced compared to the 100uF.

In attach the pic of the signals at grid of video amplifier (TP5)
and node between F902 and K112.

I hope tomorrow I will get more news.

bye

[Electronic M]

Whenever the wrong value part is installed in a set it usually means one of three things:
1.) Production change. Midway through production part values are sometimes changed to reduce the number of sets that, after being built need further work to function well enough to leave the factory. In short to lower the dud rate.
2.) Technician compensation. Sometimes repair techs who can't locate the source of a problem will change the value of a correct part to fix it. Basically treating the symptoms not the disease. It is bad practice, but is sometimes the only way to get the job done.
3.) Human error. Someone could have accidentally installed the wrong value. Or you are looking at different capacitor in the circuit than the one you think you are looking at (I've done that more than once).

[lucvic]

Effectively the cap is soldered in a suspicious place,
if I can tonight I will post the printed board
schematics where the cap I didn't find.
I hope no mistake I made.

[Sparky]

That 1nF would be more in line with the proper value. I am curious what is the the signal looking like (P-P) on the plate of the 15TP7 and the cathode of the CRT? Also, could you post a clearer picture of the video section as I cannot read the fine print. One area in question is the left section of the 16TP8. Does it say blanking driver?

Originally Posted by lucvic

Hi,
in last week end no time to work on this,
but this evening I found two things:

1) R557 increased from 5.6Meg to 27Meg ( tomorrow I will change)
2) someone in the past changed C549 (cathode of final video amplifier)
from 470pF to 100uF. I don't have one, I put a 1nF but the contrast in the
screen is very reduced compared to the 100uF.

In attach the pic of the signals at grid of video amplifier (TP5)
and node between F902 and K112.

I hope tomorrow I will get more news.

bye

[lucvic]

I hope this pic will be clearer...
if your question is
regarding the 16tp8 text "canc or" ==> "horizontal blanking"

[Sparky]

The text is still not readable but that's OK, I understand now what it says. That was the question.
Have you been able to take some measurements with a scope on the plate and cathode yet?

Originally Posted by lucvic

I hope this pic will be clearer...
if your question is
regarding the 16tp8 text "canc or" ==> "horizontal blanking"