UK Vintage Radio Repair and Restoration Powered By Google Custom Search Vintage Radio Service Data

Go Back   UK Vintage Radio Repair and Restoration Discussion Forum > Specific Vintage Equipment > Vintage Television and Video

Notices

Vintage Television and Video Vintage television and video equipment, programmes, VCRs etc.

Reply
 
Thread Tools
Old 12th Oct 2017, 1:10 pm   #41
1100 man
Hexode
 
1100 man's Avatar
 
Join Date: Apr 2016
Location: Ventnor, Isle of Wight, & Great Dunmow, Essex, UK.
Posts: 300
Default Re: My first antique TV-Olympic Model 755-need help.

Hi Chris,
Don't loose heart!! Changing all the capacitors is really only the starting point for a restoration Only once all the caps likely to cause problems have been done can fault finding & repair actually start!! I don't even apply power until I've tested/ replaced likely caps, done cold checks on resistors and potentiometers, reformed/ replaced the main electrolytics and heated up the line o/p transformer. By this point there is a fair chance that nothing nasty will happen when power is applied and that the LOPT might survive! There will still be a whole bunch of faults to sort out until good pictures and sound are achieved
You have done well to get to this point, but now you need to apply some more methodical fault finding. Study the circuit diagram. Measure the valve voltages: are they roughly what would be expected on each IF stage and also on the video amplifier?
You may have one or more faulty valves which will add to the confusion!! Measure the windings of each IF transformer for continuity (with close reference to the circuit diagram) These can sometimes go open circuit as the wire is very fine.
It's well worth studying exactly how the signal side of a TV works and how the sound, sync pulses and video information is extracted from the original RF signal at the aerial input. This makes fault finding much more meaningful and rewarding.
Good luck
All the best
Nick
1100 man is offline   Reply With Quote
Old 12th Oct 2017, 1:47 pm   #42
Argus25
Heptode
 
Argus25's Avatar
 
Join Date: Oct 2016
Location: Maroochydore, Queensland, Australia.
Posts: 608
Default Re: My first antique TV-Olympic Model 755-need help.

Chris,

I would echo the words of 1100 man.

With your level of experience here, there will only be so much you can do.

You can do all the basic checks and it might be possible that you will find the fault still.

The Tuner unit and IF in a TV set of this vintage is a moderately complex arrangement for a beginner to tackle.

When the tuner is working properly the very small level incoming antenna signal is amplified by one tube and mixed (beats with) with a signal from the other tuner tube which is the local oscillator.

The beat note, or hetrodyne if you like, is a down converted frequency for the sound and vision signals that comes out of the tuner and is passed to the video intermediate frequency amplifier (IF). So for starters the tuner has to be working properly and on the correct channel setting with respect to the signal you are feeding it.

The the video IF has to be working and have the correct band pass response. Meaning that all the small screw adjustments in the coils there have to be set right (Hopefully they won't have been touched in the recent past).

The sound signal is extracted out of the video IF at the detector with a 4.5MHz beat note between the sound and vision signals (which are transmitted 4.5MHz apart) and fed to the sound IF and FM detector circuits, then on to the audio amplifier. This is called "Intercarrier sound"

If there is an excessive sound carrier signal, or response in the video IF for the sound carrier signal, it will break through into the video signal and modulate the picture. Or if the sound traps are not set right it can also break through.

Also with adjustment errors, a picture buzz can end up in the sound channel.

Assuming none of these multiple adjustments in the video and audio IF stages have been touched, the problem could still relate to a faulty component. But it might be, that to get it working you will need some help from someone with the equipment to go through it systematically and sort it out. But I think you have done very well so far.

One approach I could suggest, since its getting a bit frustrating for you could be, put the set aside for a while. See if you can get a copy of Grob's book Basic Television 2nd Edn McGraw-Hill. This explains everything you would need to ultimately fix it yourself if you got stuck and couldn't get help. Its a good book for home study. There is a lot to learn, but it would be worth it.
Argus25 is offline   Reply With Quote
Old 12th Oct 2017, 2:23 pm   #43
ms660
Dekatron
 
ms660's Avatar
 
Join Date: Apr 2011
Location: Cornwall, UK.
Posts: 4,896
Default Re: My first antique TV-Olympic Model 755-need help.

So far as I can make out the sound IF take off is via the anode circuit of the common IF amplifier not the IF vision detector.

Lawrence.
ms660 is online now   Reply With Quote
Old 12th Oct 2017, 3:12 pm   #44
Nuvistor
Dekatron
 
Nuvistor's Avatar
 
Join Date: Aug 2013
Location: Wigan, Greater Manchester, UK.
Posts: 4,390
Default Re: My first antique TV-Olympic Model 755-need help.

Yes the set does not use intercarrier sound, sound IF 21.25Mhz.
__________________
Frank
Nuvistor is online now   Reply With Quote
Old 12th Oct 2017, 3:18 pm   #45
ms660
Dekatron
 
ms660's Avatar
 
Join Date: Apr 2011
Location: Cornwall, UK.
Posts: 4,896
Default Re: My first antique TV-Olympic Model 755-need help.

Thanks, that's what I figured.

Lawrence.
ms660 is online now   Reply With Quote
Old 12th Oct 2017, 9:16 pm   #46
Argus25
Heptode
 
Argus25's Avatar
 
Join Date: Oct 2016
Location: Maroochydore, Queensland, Australia.
Posts: 608
Default Re: My first antique TV-Olympic Model 755-need help.

Quote:
Originally Posted by ms660 View Post
So far as I can make out the sound IF take off is via the anode circuit of the common IF amplifier not the IF vision detector.
oops, I had not looked back at the schematic and noted this, So Chris, ignore the remark in my post about intercarrier sound. Most USA TV's, even ones older than yours do in fact have it. The idea of it was to avoid any effects of the sound channel going out of tune with drifting of the local oscillator in the tuner. If that drifts the effects are a bit less noticeable for the vision channel as its a wide bandwidth. So on most sets when you adjust the fine tuning knob, you do it for best picture quality, and the sound signal tuning looks after itself.

So in your set, the fine tuning control would be used to peak the amplitude of the sound signal.

In any case, I suggest for now, check all the voltages in the tuner and IF area, the anode voltages of the valves, the AGC voltage, especially as noted the 140V rail. See if you can find anything abnormal. Also check the voltages across the cathode resistor of any of the valves you can as this is an indication of their plate current and if they are biased into conduction, you can compare the cathode voltages on stages with similar valves and similar cathode resistor values even if you don't know what exact voltages should be there.

Last edited by Argus25; 12th Oct 2017 at 9:26 pm.
Argus25 is offline   Reply With Quote
Old 12th Oct 2017, 10:27 pm   #47
Argus25
Heptode
 
Argus25's Avatar
 
Join Date: Oct 2016
Location: Maroochydore, Queensland, Australia.
Posts: 608
Default Re: My first antique TV-Olympic Model 755-need help.

Quote:
So in your set, the fine tuning control would be used to peak the amplitude of the sound signal.
Chris,

Sorry to quote myself, but there is a silver lining here.

I just realized while driving to work and thinking about your TV problems and how to help you with some practical advice, the fact that your set is not an intercarrier sound model can actually be used to help you fix the set.

In this design, when you feed the set's tuner in the usual way with the TV signal, there will (or should be) a position of the Tuner's fine tuning control where the sound is best. It might not be a particularly sharp peak but it should be obvious where to set it. So If you can set it there, what you really have passing from the tuner, via the first vision & sound common IF amplifier tube V8, then the sound IF amplifier stages and then to an FM detector, is just really what amounts to a standard FM radio which no doubt you are already familiar with.

So one approach in fault finding here, is to completely ignore for now any of the faulty vision functions of the set (rest of the video IF & amp stages , sync seps etc) turn the CRT brightness to zero.

Just concentrate on working on the sound receiver system and getting that right before anything else. And think of it as repairing a typical valve based FM radio. When its working the sound would be expected to be crystal clear with good volume.

So work your way systematically on testing all the way from the tuner, V8, V3, V4, V5,V6,V7 and try to get that working before moving to any residual fault in the vision system.

(The above method doesn't work well for the intercarrier sound take off method because the entire vision IF has to be set up properly for the sound IF to work.... but luckily this doesn't apply to your unique TV set )
Argus25 is offline   Reply With Quote
Old 12th Oct 2017, 10:35 pm   #48
ct92404
Tetrode
 
Join Date: Sep 2015
Location: San Bernardino, California, USA.
Posts: 51
Default Re: My first antique TV-Olympic Model 755-need help.

I just noticed there are a couple of "bumblebee" capacitors I missed (black with colored stripes). Holy cow, this thing has a lot of capacitors!! I'm going to replace them tomorrow, and I have my fingers crossed that might do something.

Could bad capacitors cause problems like this, with the sound interfering with the image? Earlier, I had to put the tv on channel 4 to get reasonably clear audio from the vcr and yet had to to put the tv on channel 3 to get any kind of discernible image. (The sound on channel 3 was just a loud buzzing). So even when I was getting a faint fuzzy image, something wasn't quite working right. Now it seems like the video and sound are both coming in on the same channel. Maybe I did "fix" something, if they're both coming in on the same channel, but then I ran into this newest problem.

I noticed on the diagram something called a "sound trap." I read a little online and is it supposed to help to separate the sound out of the video signal? If so, I wonder if any remaining bad capacitors (I thought I got them all!) could cause it to not work and maybe that's why I getting this problem with the sound interfering with the video?

If changing the capacitors doesn't do anything, then I'm going to check the voltages at the tubes as suggested. I actually haven't really done any in-depth measurements yet.

I'm still trying to be hopeful, but yeah I might have to take a break from the tv for a while if I don't start getting somewhere with it soon. I was so excited about having an antique tv like this that I've been pretty much working on it non-stop since I got it! It's turning out to be a lot harder to fix than I thought it would be.

Edit: Argus25, I just saw your post. Any silver lining is definitely welcome! I'm going to work on that!

- Chris
ct92404 is offline   Reply With Quote
Old 13th Oct 2017, 5:41 am   #49
Argus25
Heptode
 
Argus25's Avatar
 
Join Date: Oct 2016
Location: Maroochydore, Queensland, Australia.
Posts: 608
Default Re: My first antique TV-Olympic Model 755-need help.

Quote:
Originally Posted by ct92404 View Post
I noticed on the diagram something called a "sound trap." I read a little online and is it supposed to help to separate the sound out of the video signal?
Chris, once the sound IF carrier signal is split off after V8 (in the resonant circuits L5) it is better that any remaining sound IF carrier signal (at 21.25 MHz) is not amplified by the video IF amplifier, otherwise it will or could appear as sound modulation in the picture.

So you will notice a cathode trap L7 in the cathode of V10. This raises the impedance in the cathode of V10 at the sound IF frequency of 21.25MHz, crippling V10'S ability to amplify it to any great extent.

In addition, there is another trap to help eliminate sound interference, it may seem odd that it is 4.5MHz, L11 resonat circuit in the anode of V12 pin1. This is because, at that point in the circuit, the video and sound IF carrier frequencies, which in the USA system, are 4.5MHz apart, just as they are for the transmitted signals from the TV station, can beat together at 4.5MHz.

You will also notice that once the sound IF carrier frequency is split off by L5, and feeds the sound IF amplifier, in that amplifier the resonant circuits L1 and L2 are tuned (peaked on) the sound IF frequency of 21.25 and they can be just peaked on that for alignment purposes. (The FM discriminator coil L3 is a bit more tricky to set up and really needs a sweep generator/scope to get it perfect, but you don't absolutely need that and you could probably get away with it by ear).

One other thing you might notice; the video IF coils are not peaked on the same frequency, for example L4 is peaked on 23MHz, L6 on 26.5Mhz and L8 on 25MHz. This is because, for a video IF amplifier, it needs a wide bandwidth to accommodate the vision signal frequency range which for practical purposes needs to be at least 4 MHz or more wide, for a clear, crisp picture. So the video IF resonant circuits are therefore "stagger tuned" even though the actual video IF carrier frequency they are being fed with(that comes out of the tuner) is 25.75MHz I think.

This is one reason why, when trying to fix this set, it is easier to get the sound channel working first, because you don't have to worry initially at least about the stagger tuning in the video IF, if say it happened to be miles out of adjustment. The sound system can be tuned up much more easily.
Argus25 is offline   Reply With Quote
Old 13th Oct 2017, 9:48 am   #50
Nuvistor
Dekatron
 
Nuvistor's Avatar
 
Join Date: Aug 2013
Location: Wigan, Greater Manchester, UK.
Posts: 4,390
Default Re: My first antique TV-Olympic Model 755-need help.

Referring back to post 42, learning some basic TV theory would make repairing the set a lot easier for you and once you have that knowledge itís there for the next TV you repair.

I donít know that book but if Argus recommends it , it will be a good one.
__________________
Frank
Nuvistor is online now   Reply With Quote
Old 13th Oct 2017, 10:25 am   #51
Argus25
Heptode
 
Argus25's Avatar
 
Join Date: Oct 2016
Location: Maroochydore, Queensland, Australia.
Posts: 608
Default Re: My first antique TV-Olympic Model 755-need help.

Quote:
Originally Posted by Nuvistor View Post
I donít know that book but if Argus recommends it , it will be a good one.
That was a very nice thing to say, thanks for that kind remark Nuvistor.

Bernard Grob's book (Second Edn 1954) is outstanding, it even covers early NTSC color sets like the RCA CT-100 chassis. It was edited By Donald Fink. It has large size fold out schematics in it too.

Fink wrote an outstanding textbook Principles of Television Engineering also by McGraw-Hill publishing, but earlier in 1940, the technology wasn't as well advanced then, but his book contains all the early insights into the technology and at that point the audio was AM sound for American sets.

Grob's Basic television, second Edn, comes up for sale from time to time, like this one in AU for sale I saw recently, if the mods excuse the ebay reference, but it shows an image of the book:

http://www.ebay.com/itm/Basic-televi...8AAOSws4JW72xb

It is such a wonderful book, I would have to say that most things I know about television were acquired from it. I got my copy when I was about 16 years old, it is pretty tatty now, but I still use it all the time and would never part with it, it is a lifelong companion for anyone interested in analog television technology and Grob has a way of explaining difficult concepts in a concise manner that I could never master.
Argus25 is offline   Reply With Quote
Old 14th Oct 2017, 11:33 am   #52
ct92404
Tetrode
 
Join Date: Sep 2015
Location: San Bernardino, California, USA.
Posts: 51
Default Re: My first antique TV-Olympic Model 755-need help.

I'm back on track! I think I might have figured out what could be wrong!

I hooked up another working tv to the vcr, just to double check what channel the vcr was set on. (It doesn't have a channel switch like some older vcr's, it just has buttons to go up or down. But pressing them never had any effect). The other tv is a smaller portable one, but it has rotary tuning knobs. So I just flipped the knob through the channels until I got a clear image and sound. It turns out that the vcr is on channel 2. All this time, I assumed it was on channel 3 or 4, and that was what channels I was trying to get the Olympic tv to pick up a clear signal on. So I put it on channel 2, and now at least I have it on the same channel as the vcr!

My next idea was that maybe the horizontal oscillation frequency is off. I thought about that after reading a topic on another website, from a guy who was also working on restoring an antique TV. Warning, it's a LONG thread! But here's a link to it if anyone wants to read through it sometime. I definitely learned a lot from it:

http://antiqueradios.com/forums/view...p?f=3&t=269342

Before all this, I had no idea what a "horizontal oscillation coil" even was!

I set the horizontal hold knob around the halfway point, and then slowly and gently turned the "horizontal frequency" adjustment on the back. After fiddling with it for a while, I got the picture back! It was still really fuzzy, but at least I had some kind of image again. It actually does kind of make sense that I would have to adjust the frequency...a couple of the capacitors I replaced were connected to the horizontal oscillation coil. So with more capacitance on that circuit, I'd have to adjust the coil to get it back in resonance. That's what I'm thinking, anyway.

I also replaced a few more capacitors that I had missed. I swear, this tv has more capacitors than I've ever seen in my life!
I definitely saw incremental improvements after that. The picture seemed to get a little bit more stable. It's still fuzzy, but I am noticing a difference.

I also found that if I turned the volume knob up, I can now very faintly hear the sound from the vcr on the same channel that the video is coming on! (Channel 2). The sound signal doesn't interfere with the picture on channel 2. But there is interference coming from somewhere...it doesn't seem to be a signal, but more of an overall chaotic noise causing the image to be really fuzzy and occasionally throwing off the vertical and horizontal hold. I think I know what it might be. I'm really beginning to suspect the variable resistor for the "picture" control (contrast?). The knob feels kind of loose to me, and if I barely touch it, it causes a lot of static on the picture. I'm thinking that if it's worn out and not making good contact, it might be arcing and causing electrical noise. I know that old TV's are really sensitive to electrical noise. Even tv's from the 80's...I remember the tv used to go nuts whenever my mom would run the vacuum cleaner.

Another reason why I'm suspecting the picture control is that it seems like the image picks up more interference whenever there is a bright scene. Whenever the image would go from a dark scene to a light scene, it would suddenly get more fuzzy and I would have to adjust the controls to try to get the picture back. I'm thinking that on bright scenes, more current would be going through the variable resistor, and if it's making bad contact, it would cause even more electrical noise. I did check it with my multimeter earlier and the resistance looked right as I turned the knob. But I'm still very suspicious about it. I don't think it's working right while the tv is powered up. I've tried cleaning it with electrical contact spray and that isn't helping. I think it's just worn out. I'm not 100 percent sure, of course, but I'm really thinking that it could be the MAIN culprit causing the problems.

I'm going to try to replace the variable resistor and see what happens. Maybe, just maybe I'll have the tv working after that!

- Chris

Last edited by ct92404; 14th Oct 2017 at 11:40 am.
ct92404 is offline   Reply With Quote
Old 16th Oct 2017, 12:44 am   #53
ct92404
Tetrode
 
Join Date: Sep 2015
Location: San Bernardino, California, USA.
Posts: 51
Default Re: My first antique TV-Olympic Model 755-need help.

It turns out the variable resistor for the picture control would be kind of tricky to replace. It's in line with the volume knob. The shaft for the volume control goes through the shaft for the picture control. That's because the picture control is dial, and the power and volume knob is on top of it. I didn't really want to mess with it. So I decided instead to just change the capacitor that's connected to the picture control to see if that would do anythng. I did notice a slight improvement in the contrast and the picture control isn't quite as "touchy" now.

Also, I decided to use a DVD player to test the tv, instead of a VCR. I should have thought of that before. Now I can just leave the DVD on the menu screen to test and adjust the tv. The image looks better than I thought. But it's still really fuzzy and it's definitely getting interference from somewhere. I can't get the image to stabilize. One moment I'll adjust the vertical and horizontal holds and get a better picture, and then something causes it to jump around again. It comes in more clear whenever it feels like it.

I might have a clue though. There is yet ANOTHER bumblebee capacitor that was hiding on the chassis! It's hooked up between pin 3 on the 6V6 tube and the chassis. I'm confused though, because on the diagram, on page 110, the only capacitor that's connected to pin 3 is supposed to have its other lead connected to pin 4 and the audio transformer. Why do they have it connected to the chassis? The connection on the chassis is a big solder lug...it definitely looks like something the factory did. Maybe it was a change they made later on. I'm going to change that capacitor...because, why not, I've sure been having fun changing capacitors for the past several days.

If that capacitor was bad, could that cause sound to modulate or disrupt the picture? I'm thinking that, since it is on the 6v6 tube.

- Chris
ct92404 is offline   Reply With Quote
Old 16th Oct 2017, 1:50 am   #54
Argus25
Heptode
 
Argus25's Avatar
 
Join Date: Oct 2016
Location: Maroochydore, Queensland, Australia.
Posts: 608
Default Re: My first antique TV-Olympic Model 755-need help.

Chris,

I think you are referring to C18. This capacitor has the same effect, from the alternating current perspective, if it is connected across pin 3 to ground or pin3 to pin 4. In the pin 3 to pin 4 case you will see it is across the primary of the audio output transformer, this provides high frequency cut for the sound. In this instance the capacitor has very little DC component across it, just what is dropped across the transformer primary.
In the case where its grounded it has the full DC plate voltage to contend with as well as the AC currents, but that is ok if it has a decent voltage rating like well over 400V. I would use a 600V rated capacitor here with the ground connection and if you have a 1kV rated one all the better.

As you could see, pin 4 is bypassed to ground at audio all frequencies by the electrolytic caps there.

Probably a good thing you are getting rid of those black bumblebee caps, that are notoriously bad at this age, but I don't think a problem with this capacitor relates to your current picture issues. Can you post a photo of those ?
Argus25 is offline   Reply With Quote
Old 16th Oct 2017, 8:28 am   #55
ct92404
Tetrode
 
Join Date: Sep 2015
Location: San Bernardino, California, USA.
Posts: 51
Default Re: My first antique TV-Olympic Model 755-need help.

Ok, I tried to get some pictures. All I had handy was my cell phone camera. I took some pictures with the dvd on the title screen. It's an astronomy video.

The image on the tv kind of continuously ripples in both horizontal and vertical directions. It's also fuzzy, like there is a layer of static over it. That's why it seems to me like it's picking up interference from the sound. But I can still see the image and even some text is legible. I can see "Play Chapters" on the screen.

I'm attaching pictures, and the first few are of the tv when the image looks a little better. Since the image is continuously rippling a little up and down and left and right, the image looks blurry in the cell phone picture. The real tv image is a tiny bit better than the cell phone picture.

One weird thing is that there is a black bar going down the right side of the image. No matter how much I try to adjust the horizontal hold or horizontal frequency, I can't get rid of it. I have no idea what's causing it.

Then all of a sudden out of nowhere, the image will go nuts. It gets distorted and starts shaking horizontally. You can see this in the 4th picture I attached. If I leave the tv alone for a few seconds, it will "fix" itself and the image will stabilize again. But only temporarily.

The 5th picture is a screen shot I took from my computer with the DVD on the title screen, just so you can see what it's supposed to look like.

Any ideas what could be happening?

- Chris
Attached Thumbnails
Click image for larger version

Name:	tv better image1.jpg
Views:	88
Size:	41.0 KB
ID:	150833   Click image for larger version

Name:	tv better image2.jpg
Views:	79
Size:	40.5 KB
ID:	150834   Click image for larger version

Name:	tv better image3.jpg
Views:	77
Size:	31.4 KB
ID:	150835   Click image for larger version

Name:	tv distortion.jpg
Views:	81
Size:	27.4 KB
ID:	150836   Click image for larger version

Name:	screen shot.jpg
Views:	72
Size:	54.8 KB
ID:	150837  

ct92404 is offline   Reply With Quote
Old 16th Oct 2017, 11:04 am   #56
Argus25
Heptode
 
Argus25's Avatar
 
Join Date: Oct 2016
Location: Maroochydore, Queensland, Australia.
Posts: 608
Default Re: My first antique TV-Olympic Model 755-need help.

Some of that patterning on the image looks like carrier wave interference, in other words another signal there interfering with the main signal. Possibly, some could be chroma sub-carrier interference (the color signal that rides on the luminance signal) causing interference.

Probably, you do not have a signal generator that generates a definite known good monochrome test pattern and modulates that onto a specific RF carrier & channel frequency. This is the type of box (test equipment) that a TV repair person would use to feed the set, to make sure the source signal was known to be good & stable.

The next best move; get the signal you are using to feed this TV and feed another known good working black and white TV set, and see what the signal looks like on that.
Argus25 is offline   Reply With Quote
Old Yesterday, 7:26 am   #57
ct92404
Tetrode
 
Join Date: Sep 2015
Location: San Bernardino, California, USA.
Posts: 51
Default Re: My first antique TV-Olympic Model 755-need help.

I replaced C18 today, and I decided to connect it between pin 3 and the chassis, the way it was connected originally on the actual tv. I'm using a .01 microfarad capacitor, rated at 1.6kv, so it should be fine with the plate voltage.

There might be a very slight improvement with the picture...it seems like it holds steady for a little bit longer. But there is still definitely interference coming from somewhere.

Argus, I don't have another black and white tv to test the signal. It's actually pretty hard to find them now. I could look around in a thrift shop though, and maybe if I got lucky I could find an old portable B&W tv from the 80's or something. Usually whenever I find CRT tv's, they aren't that old, just from the late 90's or early 2000's.

I think at this point, I'm going to have to systematically check the voltage in every part of the circuit and see if it matches up with what's shown in the diagram. As I check each line, I'll mark it on the diagram with a green highlight marker if it measures good. I don't have any fancy equipment, all I have is a multimeter. (Well, I do have a vintage Heathkit capacitor checker but who knows how reliable THAT thing is!) So pretty much all I can do is just basic voltage and resistance measurements. Still, if the voltage isn't right somewhere, that might give a clue about where the problem could be.

I don't really know how TVs work, so I can't approach it in a diagnostic way. I understand that the CRT forms an image by "painting" it line by line with the electron gun and that the electron beam is controlled by deflection coils at the back of the tube. But that's pretty much ALL I know! I'm definitely going to have to do some reading! I'm planning to get that book you mentioned. I actually saw it on Amazon.

- Chris
ct92404 is offline   Reply With Quote
Old Yesterday, 8:23 am   #58
Argus25
Heptode
 
Argus25's Avatar
 
Join Date: Oct 2016
Location: Maroochydore, Queensland, Australia.
Posts: 608
Default Re: My first antique TV-Olympic Model 755-need help.

Quote:
Originally Posted by ct92404 View Post
I don't really know how TVs work, so I can't approach it in a diagnostic way. I understand that the CRT forms an image by "painting" it line by line with the electron gun and that the electron beam is controlled by deflection coils at the back of the tube. But that's pretty much ALL I know! I'm definitely going to have to do some reading! I'm planning to get that book you mentioned. I actually saw it on Amazon.

- Chris
Well, with what you have achieved so far with the limited knowledge and experience with the task I think you have done remarkably well, so you must be very smart and quick to catch on. Take a break from it and get that book. Once you have read it, a lot of the pieces of the puzzle will fall into place and you will know what to do with your set. It will be a great journey of discovery.

Hugo.
Argus25 is offline   Reply With Quote
Old Today, 9:24 am   #59
ct92404
Tetrode
 
Join Date: Sep 2015
Location: San Bernardino, California, USA.
Posts: 51
Default Re: My first antique TV-Olympic Model 755-need help.

Hugo, thank you for all your help, and your kind comments. I'll probably take a short break and then I'll start doing voltage and resistance measurements on the circuits. Up to this point, my only strategy has been to just replace parts and hope that I get lucky. That did get the CRT to come back to life, and now there is an image at least. There's definitely something still wrong though. But now I've replaced all the easy parts and fixed the obvious problems. I think the only capacitors left are mica caps, and I've read conflicting opinions about whether they should be replaced. I'll probably have to do a more methodical check of the voltage and resistance point by point, before I just arbitrarily mess with the mica caps.

I'll get that book soon. I like collecting vintage books too.

I'll post an update if anything measures way off, or if I have any other clues.

- Chris
ct92404 is offline   Reply With Quote
Reply

Thread Tools



All times are GMT. The time now is 6:42 pm.


All information and advice on this forum is subject to the WARNING AND DISCLAIMER located at https://www.vintage-radio.net/rules.html.
Failure to heed this warning may result in death or serious injury to yourself and/or others.


Powered by vBulletin®
Copyright ©2000 - 2017, vBulletin Solutions, Inc.
Copyright ©2002 - 2017, Paul Stenning.