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-   -   Bang and Olufsen LX2802 TV advice (https://www.vintage-radio.net/forum/showthread.php?t=126013)

justanotherhigh 1st May 2016 11:57 am

Bang and Olufsen LX2802 TV advice
 
Just lost my beloved B&O LX2802 late 80s tube set. No before symptoms, turned it on last week and got sound but no picture. You can hear the tube start (I am sure you guys know the noise) but it stays just completely black. When you turn it off you still get the white flash. Have looked in the set, nothing immediately obvious, checked all the boards for visible poor soldering. I need some pointers on where I should be looking, I dabble in electronics and deal with industrial electrical for a living, but I don't really know the ins and outs of TV fault finding. Any thoughts? Much appreciated!

Red to black 1st May 2016 12:55 pm

Re: Bang and olufsen tv advice?:)
 
Try turning up the A1 or G2 control (second pot down) on the lopt (mark it first), and see if you have frame collapse.

justanotherhigh 1st May 2016 3:52 pm

Re: Bang and Olufsen LX2802 TV advice
 
Cant find any pots labelled A1 or G2, there are two unlabelled on the lopt. Marked and adjusted each one, one made no difference at all, the otherat one end of its travel produced a mergey picture of blues and greens across the whole screen

Studio263 1st May 2016 4:27 pm

Re: Bang and Olufsen LX2802 TV advice
 
This fault is normally caused by a duff colour decoder IC, random flashovers in the tube can damage it. I've got loads of panels for these, PM me if you would like a set for the signals side (that should get it going).

While you are there, make sure that a link has been added between the emitter of the line output transistor and ground. Originally this went through the scan coil plug to disable the line output stage if the coils were unplugged, however it only takes a slight increase in resistance at any of the various contact points to ruin the transistor so its best to disable the arrangement (as B&O recommended at the time). The electrolytic capacitors in the base drive circuit of the line output transistor should also be replaced if they look a bit care-worn, use Matsushita 'FC' series ones (from RS Components etc) as a durable replacement. That's another B&O tip from the period, these sets developed a reputation for random line transistor failures when they were only a couple of years old but these measures fix that.

Also note that the wiring is a bit flimsy and apt to break where it goes into the various plugs that link the PCBs together (most especially the white stuff). Wires can snap off anywhere so it is worth giving anything in the suspect area a little tug to make sure that the cores haven't broken under the insulation, many hours of my time have been wasted tracing the results of this little problem.

justanotherhigh 1st May 2016 5:05 pm

Re: Bang and Olufsen LX2802 TV advice
 
Much appreciated, sent you a message!:)

Red to black 1st May 2016 5:41 pm

Re: Bang and Olufsen LX2802 TV advice
 
I had half expected a frame fault as this blanks the screen too, however S263 is looking after you now. :)

justanotherhigh 30th Jul 2016 8:08 pm

Re: Bang and Olufsen LX2802 TV advice
 
Awakening this topic again, at my wits end with this set. Now I am a sparky on all sorts of big electrical kit but not exactly electronics.
Same symptoms as previously mentioned. A kind member has sorted me out with a set of signal boards which made no change when fitted. Tested a load of components on the output board, found HOT useless. Replaced with equivalent parts now tests out ok, at the same time made the ground mod copied from an L2500 i obtained. Powered up, no change. All caps and other transistors appear OK, diode D34 seems a bit wobbly... anything else likely to cause this problem?

Mad Mal 4th Aug 2016 10:41 pm

Re: Bang and Olufsen LX2802 TV advice
 
Not sure if this will help... EsI have the service manual. Just found the link.
http://www.eserviceinfo.com/index.ph...hstring=LX2802
It's a winrar file and will need to be unrared to make it viewable on a PC.


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