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Faulty Toshiba TV 2505 DB

Our TV developed a fault over several months and was eventually beyond a joke - when Christine threatened to throw it out, I decided to attempt a repair on it. The screen had shrunk vertically until it was like watching a movie in the letterbox format!

So, after posting a message on sci.electronics.repair newsgroup, I was told by a few people that it was possibly a defective capacitor near the vertical IC?! A bit more tracking down on the net and I found I was looking for a 2.2uF cap near IC371. Another good website I came across whilst looking for information was http://fileshare.eshop.bg/repair_tips.php?search_rt=2505DB.

I hate TV's - they frighten me with all that HV stuff, but now was the time to remove the case and get in there. Now, I haven't been in that many TV's (because of above) but this was by far and away the dirtiest I had ever been in! Mind you, vacing the dirt out gave me time to pluck up courage to tackle the HV lead to the tube. Eventually I plucked up courage and shorted the HV lead to the earth wire on the back of tube with a large screwdriver and only got the tiniest little spark - phew! The wiring loom was tywrapped into place so I took some photos so hopefully I knew where everything went for reassembly before cutting the loom free. The photos below are taken AFTER the TV had had a good vacing with a dyson!

I then removed the connectors (I had to desolder the mains and HV earth connectors) and pcb tray and took the whole assembly to work to give it a clean with a compressed air line. It then got a brushing with a small paintbrush to remove the stubborn dust/dirt that had got stuck between the components and a final blast with the airline. Anything that could be removed and washed, was (i.e. plastic carrier tray, back audio video connector panel etc) while the insides of the TV were given a wipe over with a damp cloth (I hate working on dirty equipment!). At last I could find the components I was looking for!

The area you will find the IC/cap in is the on bottom left hand side of the picture above and shown magnified below (IC371 & C372).

I used my trusty Elektor Electronics capacitor ESR tester (September 2002 issue) and found that the cap had an ESR of 185R (in circuit) so it was pretty conclusive that this component was duff, especially that distinctive capacitor smell that it made when I desoldered it. Just out of interest I used my multimeter on capacitance mode and the cap read about 3.3uF, so without the ESR meter you may well have thought there was nothing wrong with it. Shortly after I took the photo below (sorry I left the camera in Macro mode - doh!), the leg dropped off the cap! 

I didn't want to be going back inside the TV so I took the decision to change the IC at the same time as it was only about £3, even though I doubt it was faulty. The offending components are shown below.

I got the replacement IC from www.dalbani.co.uk and the 2.2uF cap from www.cpc.co.uk - I didn't know the other specs of the cap, so I just got a low leakage Rubycon cap. I measured the ESR of the new cap before fitting and it was 2.5R, so quite a difference!

I'm glad I took plenty of pictures before I disconnected everything as I don't think I would have got it right first time if I hadn't had something to refer back to. Needless to say, everything was a lot less dirty when it went back than when I first opened the set up.

Now was the moment of truth, time to switch on!

Whey Hey! Success! A bit of fiddling around with the picture size and adjustment controls (they had been set to their extremes when the fault first developed to try to counteract the effects) and we were back in business:

Another successful repair job, time for a beer and to watch some now undistorted TV!