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Toshiba CRT TV fault... what could the problem be?

Discussion in 'Troubleshooting and Repair' started by alex1878, Aug 11, 2016.

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  1. alex1878

    alex1878

    15
    2
    Aug 11, 2016
    Hello!

    I have got a faulty 25" CRT TV to ask you about - it is a Toshiba 2573DB, and it is from 1997, I believe. I got this television in 2008 and it has been fantastic for retro gaming for many years... until a couple of weeks ago. I was moving the television downstairs and I temporarily placed it onto my sofa, thinking it would be secure enough for a few minutes. Unfortunately, it must have very slowly rolled forward (being so front-heavy) and I heard a loud bang about five minutes after leaving it on the sofa. The TV had fallen about 40cm from the sofa and landed directly on its head on the floor. :(

    When I originally plugged the TV in after its fall, the TV would not come on and would just make a "click" sound whenever I pressed the power button. At this point, I thought it was dead. However, I have been trying to turn on the television every few days since then in the hope that the situation will change (it was just such a good TV)... and yesterday, it did!

    Yesterday evening, the television actually came "on", in the sense that I could hear it booting up with the degaussing "clunk" followed by the high-frequency noise that all CRTs make. I do not know why it started up yesterday after looking like it was dead, but it now comes on every time (I tried it again today a few times) - however, there is no picture.

    When I press the power button, the screen flickers in the corners for a few seconds, but no full picture. And when I turn the TV off, there is a brilliant white flash in the centre of the screen. Aside from this, the screen is black while the TV is "on", but the sound works perfectly (I tested a games console with it). I can also tell that the TV is operating correctly because I can switch channels and sources with the remote control.

    Please watch a short video I made today which clearly shows and explains the issue...


    The reason I made this thread is that I was wondering if any of you have any ideas of what the problem might be here. I haven't opened up the television because I have extremely limited knowledge of CRT TVs, and I know it is dangerous if you don't know what you are doing. It is out of interest, more than anything, that I ask for your suggestions on what the issue could be. I am fascinated by how CRTs operate and find them very interesting devices. If I could get it repaired by someone, I would, because this TV really is fantastic.

    Thank you for your time! :)
     
  2. Heliman

    Heliman

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    13
    Feb 4, 2016
    It appears your not getting any sweep of the beam, likely a problem with either high voltage or the yoke itself. Try taking the back off the TV and look for any connectors that may have come loose from the fall. Be careful though, capacitors and the CRT itself stores high voltage for long periods of time even when unplugged.
     
    alex1878 likes this.
  3. Heliman

    Heliman

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    13
    Feb 4, 2016
    Another suggestion, probably even a easier solution. Check Craigslist under free stuff. People are giving away TVs like the one you have on a daily basis. Most say in perfect working order, they cant throw them away so they give them away.
     
  4. alex1878

    alex1878

    15
    2
    Aug 11, 2016
    Thanks for your response. Do you think then, that it's not a problem with the tube itself? I was hoping it wasn't the tube, because I've read that if it is then you basically can't repair them.

    I have never opened a CRT before so I'm a bit nervous about doing so - should I leave it unplugged for a few days to discharge it? Anything I shouldn't touch if I do open it up?

    I actually bought a CRT locally via eBay a few days after mine stopped working, so I have got one set up that works. However, it's not as good as my Toshiba, as all of the colours bleed a couple of centimetres to the right... on a side question, what could cause that? :D

    In any case, I would really like to try and get the Toshiba working again if it isn't something major, so I might try opening it in a few days after I have discharged it.
     
  5. Heliman

    Heliman

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    13
    Feb 4, 2016
    You need to stay away from any filter capacitors and the HV lead where it attaches to the CRT. Its not hard to discharge if you have a grounding lead with a probe. Its a possibility the fall could have damaged the guns in the neck of the tube but I think its a high voltage problem. With colors bleeding its a convergence problem. A simple adjustment of the magnets on ring behind the yoke will fix that.
     
    Last edited: Aug 11, 2016
  6. Heliman

    Heliman

    65
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    Feb 4, 2016
    A trick I use to find loose connections that works 75% of the time is, use a 3/8 or similar wooden dowel rod about 2 feet long. While the set is on use the rod and depress areas of the circuit board. If you notice a change in the TVs operation, investigate that area looking for cold solder joints or connections. Saves alot of trouble shooting time with a 50 cent tool. Just need to be careful anytime while in the back of an old TV when its plugged in or unplugged for that matter. I got shocked 40 years ago by a CRT. It was a lesson well learned, never got shocked again.
     
  7. Sunnysky

    Sunnysky

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    118
    Jul 15, 2016
    I agree it is a HV problem. The flyback transformer operates at high audio f is making the noise and is connected to high voltage rectifer caps called voltage doublers which if touched will give a big shock , even after a long time..

    Since the sound continues, it is working but with an arc inside.

    The little transformer will have heavy insulated wire and may have been rattle enough to cause leads to have moved causing an internal short when turned on. YOu may learn lots trying to fix it. But if you don't understand the risks, don't try it. 25kV can arc between 1 -2 cm air gaps. TV techs would use a screwdriver and jumper to chassis ground to discharge any doublers for 10 seconds before getting close.

    Dust can also be charged up around the flyback and can cause an arc too. So electronic spray cleaners or paint brush with isopropyl are sometimes used... carefully.

    If you have ever felt a car ignition spark plug , it will activate all your muscles and you react in pain if not lethal thru both hands to the heart.

    They give these TV's away here or go to the junk yard.
     
    Last edited: Aug 11, 2016
    alex1878 likes this.
  8. alex1878

    alex1878

    15
    2
    Aug 11, 2016
    Thanks both for your helpful info. I think I may open it and look for anything obviously loose but not go much further than that.

    Sunnysky, since you say the arc might be inside the flyback transformer, do you think replacing the flyback transformer would be something to try? Is this particularly dangerous or does it just involve some soldering?

    I was actually about to take the TV to be recycled when it started to come on again. I'm guessing the fact that it just clicked before and did nothing was because the electricity wasn't arcing across a gap, but now it is managing to.
     
  9. Heliman

    Heliman

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    13
    Feb 4, 2016
    To replace a flyback youd have to check and re-calibrate the high voltage settings. You need a HV probe for a volt meter which is kinda expensive.
     
  10. Heliman

    Heliman

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    Feb 4, 2016
    This video shows how dangerous HV discharge can be.
     
  11. debe

    debe

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    Oct 15, 2011
    Colour bleeding is most likely a small Electrolytic cap on the RGB circuit on the board pluged on to the neck of the tube. The capacitor dryes out & usualy a 250V cap.
     
    alex1878 likes this.
  12. Sunnysky

    Sunnysky

    470
    118
    Jul 15, 2016
    I would inspect the flyback for dust and short out connection to doubler cap with a grounded alligator clip jumper to tip of a clean insulated screw driver.

    Try vacuum or clean doubler and flyback with paint brush and lots of isopropyl. alcohol.

    If not too dusty, toss it. Dry well with fan before trying.

    TV repairmen used to keep one hand in pocket to avoid shocks thru the heart !

    in the nice arc video above the HV is disconnected by the ground contact which connects to the back of the tube.
     
    Last edited: Aug 11, 2016
  13. john dougherty

    john dougherty

    9
    1
    Feb 11, 2013
    Sounds like you have a line circuit problem . The high pitch whistle you hear is the line frequency and drive the EHT about 1200 to 1500 volts to give E H T to the crt . As you switch off the the line and frame circuits collapse because there is no ht to drive the circuit . However it sound more like a Video fault and perhaps with the fall the tele may have a break in one of the circuit boards or a broken wire from the base of the Tube . fred sharpe electronics
     
    alex1878 likes this.
  14. davenn

    davenn Moderator

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    1,869
    Sep 5, 2009
    actually, usually around 20 - 25,000 V
     
  15. alex1878

    alex1878

    15
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    Aug 11, 2016
    OK, based on all of your responses, I think that the problem with my Toshiba would be too difficult to repair for me. I wouldn't feel at all confident with all of those high voltages present! If I had more experience then maybe I would try to repair it. I feel like I have learned a lot from your replies and suggestions though, so thanks! It's nice to know what could have gone wrong inside and to get more knowledge on CRTs.

    While I'm here, here are some pictures of the colour bleed on my working CRT: (it's probably much easier to fix!)
    IMG_20160812_110611.jpg IMG_20160812_110651.jpg IMG_20160812_110859.jpg IMG_20160812_110927.jpg IMG_20160812_111111.jpg

    As you can see, it's very prominent with white-on-black. The bleed does happen with all colours, it just seems to be worse the lighter the colour is (and the darker the background). It can be pretty annoying!

    Heliman - are you sure this could be fixed using the convergence controls behind the ring? I thought the convergence controls were for when you could see the separate red, green and blue colours on-screen, incorrectly aligned. This TV is just leaving long streaks after everything - maybe a capacitor change is needed, as debe suggested. This sounds like an easier repair than the Toshiba ;)
     
  16. debe

    debe

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    Oct 15, 2011
    Unless you have experience in seting up Convergence & have access to a Cross Hatch Generator, Don't go there. Its more likely the Video Output stage power supply capacitor. Convergence is unlikely to have altered. Post a clear picture of the component side of the board on the picture tube.
     
  17. debe

    debe

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    Oct 15, 2011
    Un fortunately Ive thrown out most of my CRT TV workshop manuals. But ive found an NEC circuit that shows the capacitor C543, 33uf 250V that will cause the problem you describe NEC CTV VIDEO DRIVE.jpg
     
  18. alex1878

    alex1878

    15
    2
    Aug 11, 2016
    Thank you for the diagram and info. It will probably be a few days before I have the time/space to take the back off that TV. But if I locate that part and want to replace it, that will just be a matter of de-soldering and soldering again, right? And being 250V, will I have to take precautions when removing it?

    Finally... will these capacitors be readily available or will they be hard to get hold of?
     
  19. debe

    debe

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    64
    Oct 15, 2011
    Should be easy to remove & re solder, Should be readily available. When you do get to it post a picture of the component side of the board.
     
  20. john dougherty

    john dougherty

    9
    1
    Feb 11, 2013
    I cannot help much more as you will need a diagram to find your way around the circuits and this will give you the readings required
     
    Last edited by a moderator: Aug 15, 2016
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