Hi all,
I've been following this forum for a while now and have gotten many helpful tips. This time, I have some questions concerning an old Sony TV that's been following me for almost all of my life.
The TV has given me all kinds of trouble over the years and went through several SG613s before I changed the circuit to a regular HOT. Also, at some point there were issues with the H Stat, the three beams started wandering around like crazy. After fixing these issues, the picture was always pretty good, minus some geometry issues. I also went through the set and replaced most electrolytics and checked the ones I didn't replace with a tester.
Over the years, the b/w picture remained pretty much unchanged and with excellent clarity, however some issues with colors started to develop. The set is very sensitive to the source of the image, it has serious issues with some VCRs (colors are completely wrong, the blue menu background is a dark shade of purple or has no color at all). As I have the service manual for the set, I decided to perform a bit of a calibration, and that's when I ran into some strange issues. I am hoping someone on this forum can maybe give me a few pointers in the right direction...
One of the first steps in the manual is to check and adjust the AFT. In its current state, the AFT is not working properly, when turned on, the colors all but disappear and the image is far from ideal. Going though the procedure in the manual, adjusting the coil (AFT-T3) proved difficult, as the ferrite core was stuck and crumbling. After replacing the core, I still could not detect an effect of the adjustment on the picture. Turning AFT off produces a much clearer picture. Any ideas what could be the issue here?
I proceded with other color adjustments, but they do not have the effect on the signal waveforms as described in the manual. Generally, I am dealing with some issues here, as all the abbreviations (BAT, AFT, DMP...) are difficult to interpret for me, as I have not been able to find a list with the full terms. This would make it much easier for me to relate them to the corresponding German terms.
The main issue with the set is, that the best tuning for the picture does not coincide with the best color image. It is either a clear b/w picture, oder bright and clear colors. Any pointers on what to check? The color image is generally a bit uneven, with varying color intensity from top to bottom. This can be seen a bit in the image below. I am not talking about the darker area across the whole screen from photographing, but the small darker area in the blue bar towards the right bottom corner.
I really hope to get this TV back to a proper working state, it seems like seemingly minor issues like these are ofter harder to fix than big things, like a set that won't do anything.
Thanks for all the help in advance!
Gunther
@gschwab I can't really help with your fault I'm afraid. I didn't see a lot of Sony sets back when I was in the trade and those I did see were usually straight forward faults thankfully. (1810UB excepted!) I can relate to being very fond of a set which has been owned for a long time as I have two sets myself that I have owned since my early teens, one a colour set my parents bought new. I can only suggest getting a 'scope on the set and checking to see if any waveforms in the IF or decoder can give you any pointers. I heard somewhere that Sony transistors can get a bit 'iffy' with age...
Good luck with it!
Rich
@slidertogrid thanks a lot for your kind words! I think you are right, I will just have to go through it and see where things start going wrong. It's too bad the service manual is not that comprehensive, despite consisting of quite a few pages...
Any ideas where I could find information on the abbreviations used?
Well, some progress. The signal after the video detector definitely doesn’t look the way it should.
Looks like somewhere in the IF decoder, the amplitude is limited. There are still 3 electrolytics to check in there, of course everything is under a cover soldered to the PCB…
Looks like it's crushed at the bottom, bias resistor around the detector?
Time to check some voltages
@irob2345 exactly! Need to remove the cover and start measuring. Glad I found an explanation for what I‘m seeing on the screen
Well, that didn’t go exactly as planned. An electrolytic decided to go up in smoke, creating a short and taking an inductor with it. Will have to find a replacement and hope that not too much damage was done. Before this happened, I measured the voltages around the transistors in the IF circuit, everything seemed pretty normal. Maybe it is an issue with a transistor, as mentioned by @slidertogrid…
Well, that didn’t go exactly as planned. An electrolytic decided to go up in smoke, creating a short and taking an inductor with it. Will have to find a replacement and hope that not too much damage was done. Before this happened, I measured the voltages around the transistors in the IF circuit, everything seemed pretty normal. Maybe it is an issue with a transistor, as mentioned by @slidertogrid…
You can probably say that capacitor was way below par before it finally smoothed it's last.. that maybe the root cause of your issue. Post up the part no of the inductor and hope someone was one or something similar.
TV is back to where it was, before I continue, I want to make sure the signal I‘m feeding in is ok.
The image on the left is still pretty weak, gets progressively better towards the right side.
I am using the color bars created by an HDMI to Scart converter, fed into an old VCR. Not ideal, but that’s what I intend to use with this TV once it’s working properly again.
I have an old test image generator that works ok, but going through it to make sure the signals are up to spec before continuing. Another rabbit hole 😝
What is it like in black and white? Shading like that can be caused by poor decoupling of the supply to the RGB stages.
@sideband unfortunately, the picture I took is terrible. The B/W picture is ok, it only seems like the brightness on the left side of the screen should be a bit higher. It all corresponds very well with the oscillogram of the video signal that I posted. The big question is why the amplitude on the left side of the signal trace is limited. Almost all electrolytics in that area have been replaced by now
@gschwab The capacitor in question often resides on the neck board. It decouples the HT to the output stage. Basically, it gets a kick of charge at the start of the scan line, but (if knackered) runs out of puff by the end. This won't be the case in black and white though, although you probably won't see it on a grey scale pattern. Have you got a real picture source, or test card F etc to try?
@doz very interesting, will definitely check that capacitor! Generally, I would say that the b/w picture is ok, maybe lacks a bit of contrast. The video signal at the end of the IF stage definitely isn’t ok. While I can adjust the overall signal amplitude in relation to ground, the AC amplitude of the signal is too small, resulting in too high a voltage level at the base of the output transistor directly after the detector diode.
I am not super confident about the quality of my video source, even though it works fine on other TVs. I will hook up a DVD player with a modulator to investigate further. Any recommendations for a test image DVD that doesn’t cost a fortune?
There was a free download somewhere ... it'll be PAL though, and I'm not sure where you are in the world.
And there is, of course, PiPatGen ... https://andydoz.blogspot.com/2023/02/pipatgen-raspberry-pi-television.html
While you are setting up your Pi there was a downloadable DVD test card reference on UKVRRR. See post #47, you will need to burn the iso to DVD.
https://www.vintage-radio.net/forum/showthread.php?t=71637&page=3
Frank
@nuvistor thank you, that will probably speed up the process! I’m out of town this weekend, hope to make some progress next week
And there is, of course, PiPatGen ... https://andydoz.blogspot.com/2023/02/pipatgen-raspberry-pi-television.html
Meanwhile, this has made me somewhat angry.
Pity I was banned from there - my response would have merited a ban. It's interesting that they have such a relaxed attitude to intellectual property over there, unless it's Paul's service data of course.
