Italian 1962 TV B&W
 

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

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.

here's the schematics

thank you

Nice to have you ! Welcome !

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 ?

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.

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

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

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.

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

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).

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.

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?

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

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?

In these days I don't hve my camera,
I hope tomorrow yes, plate of 15tp7 and cathode of
CRT correct?

Hi guys,

last evening I tried to make a photo of the signals requested
but I found a new issue.
The signal at the videodetector was suddenly disappeared.
Seemed a bad contact but in 2 hours I didn't fix this.
After various simple checks I was very sad of this but the
signal magically re appear. Can this be a problem on high frequency
down converter or oscillator?
This set have two inputs VHF and UHF and two different tuners.
Since starting on this project I have used a VHF signal I didn't try to switch on the UHF signal.
I will try again to fix the issue tonight.

thank you

here I am,
today I had some time to work on this TV.
I found some differences in voltages at electrolytic caps
(anodes of the tubes).
This difference was because I substituted the the diodes (2 PY82) with one 1n4007 with a resistor 82 ohm in series. This was a mistake because the 82 ohm is the resistance of one tube but the PY82 are connected in parallel.
Now the vertical sync is more stable but the sound have some troubles yet.
ASAP I will post some images.

thank you for your help

Hi dear all,
some work on this project in these days,
I found some docs on this set,
various vawes are shown and the first I see is the amplitude
at grid of output video amplifier.
The value I have i 2.5V pk to pk.
This value in doc is between 2.5 to 8 V pk to pk.
So I figure there are troubles in tuner or IF, or a overload of these two
sections.
AGC seems to work propely because bias of IF tube increases if I slightly disconnect the antenna.

Any suggestion on verify I can do?

many thanks