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Old 5th Dec 2013, 10:30 pm   #21
Nuvistor
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Default Re: Crackling Inside Beovision 7802

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Originally Posted by AC/HL View Post
The Aquadag doesn't extend to the connector, there is a patch of clear glass around it.
Yes outside but I was meaning the DAG coating on the inside of the glass where it connects with the Final anode socket. The thought was that too much current there could damage the joint where the anode connector and DAG meet. It was only painted over and would be a thin film.
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Old 5th Dec 2013, 11:02 pm   #22
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Default Re: Crackling Inside Beovision 7802

I was replying to Okto, but I suppose a large CRT could hold quite a bit of energy. I've also discharged them with a short, but it has never caused any damage.
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Old 5th Dec 2013, 11:18 pm   #23
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Default Re: Crackling Inside Beovision 7802

Sorry, I thought you were replying to me.

It is one of those things that may never happen, it was just classed as best practice where I was.
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Old 5th Dec 2013, 11:30 pm   #24
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Default Re: Crackling Inside Beovision 7802

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Originally Posted by Welsh Anorak View Post
Don't be tempted to try and improve the scratch
I think you're right, using abrasive polish on the screen is likely to make it worse. So it will just have to stay.

As for the switches, both my sets (Beovision 9000 and 7802) are now permanently stuck in the on position. Maybe I'll try to replace them some time (although difficult to change doesn't sound so good). I'm currently not sure if I can get a new switch anywhere anyway, and it isn't essential.

The only remaining problem with this set is a puzzling buzzing from the speakers/headphones. With the speakers it's there, but subtle enough I don't mind it. With the headphones, it's very annoying and seems louder. I've tried it with nothing attached to the aerial and scart socket, I've tried unplugging everything else on the circuit, and nothing has changed it. Adjusting the volume doesn't affect it either. I can only guess it's something the TV is doing itself, but it shouldn't be.

Anyway, thank you to everyone for your advice.
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Old 6th Dec 2013, 2:13 am   #25
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Default Re: Crackling Inside Beovision 7802

It is indeed best practice to use a resistor, but as long as you don't discharge the tube tens of times the damage to the inner conductive layer is probably minimal to none.
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Old 6th Dec 2013, 11:25 am   #26
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Default Re: Crackling Inside Beovision 7802

Hi
I hold my hand up to using the 'two screwdriver' method of discharge - at least you know it can't bite any more!
There shouldn't be a buzzing - check the internal wiring hasn't been disturbed, especially the scan coil leads. It could be a capacitor but somehow I doubt it. Ideally the mains switch should be replaced, but ulike the Philips ones which used to arc and cause a hazard, in my experience these suffered from mechanical failure which resulted in them being permanently 'on'. Perhaps a B&O expert (hi Tim) could comment?
Glyn
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Old 6th Dec 2013, 11:43 am   #27
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Default Re: Crackling Inside Beovision 7802

B&O's reputation was seriously harmed when the insulating material used (srbp) for the line scan coils on the tube actually caught fire causing a number of fires and a death.
The solution was to remove a pin and its wire and sleeve it. If the material had been
glassfibre (for a few more pence) this would not have happened.
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Old 6th Dec 2013, 12:53 pm   #28
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Default Re: Crackling Inside Beovision 7802

Seen a few charred scan coil PCB's but luckily no major fires. The field service guys, as part of company policy, would either resolder the connections if board not showing signs of heat or we would just simply fit a new set of coils and bill back to B&O. But more often or not, the Mullard/Philips scan coil assemblies on these sets would hum badly due to a detached ferrite yoke. Many of these were replaced under warranty with a different scan coil assembly (I think probably ITT). At its peak we were typically changing five to ten scan coils a week.

Mains switches were a regular PITA, even the correct B&O replacements did not last long and this must have cost B&O dear since the majority were replaced under warranty. Two main problems were; broken latch mechanism and contacts welding in the on position. This points to the wrong contact material being used or excessive turn on surge current. On my own B&O, knowing the problems, the mains switch was never turned off. Instead it was switched to standby and turned off at the wall socket, reasoning being it was cheaper to replace the wall socket! Well this method worked fine for over 25 years until the tube failed, but the socket is still working fine.

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Old 6th Dec 2013, 9:55 pm   #29
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Default Re: Crackling Inside Beovision 7802

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Originally Posted by Welsh Anorak View Post
Ideally the mains switch should be replaced, but ulike the Philips ones which used to arc and cause a hazard, in my experience these suffered from mechanical failure which resulted in them being permanently 'on
Thank you - these sound like places I want to investigate, but my knowledge of components inside a TV is limited. There's a lot of wires, so I'm not sure which ones to look at or what to look for? I'm guessing that some wires shouldn't be too close to others because of interference?

As for capacitors, I'm wondering why not suspect them as they should be pretty old by now?
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Old 8th Dec 2013, 12:45 pm   #30
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Default Re: Crackling Inside Beovision 7802

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The lead from this comes out and takes a fairly tortuous route to the tube and anode cap, where a "bleed" resistor for the focus supply is fitted inline on the cable - looks like a small box.
Well, this box in the EHT cable is now arcing to the coating on the back of the tube and the TV does not work at all. I suspect this was the problem in the beginning - but my moving it around to clean under the cap must have made it worse

I'm not sure how to solve this, so it might be the end of the TV. I'll have to investigate more, but not a lot has turned up so far. Any advice would be very welcome?
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Old 8th Dec 2013, 1:51 pm   #31
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Default Re: Crackling Inside Beovision 7802

Ok, after a bit of googling, puzzling at some Danish, and a cup of coffee later I have found a new EHT cable that I believe is the correct replacement part:

http://www.donberg.ie/catalogue/line...s/hr_1689.html

I don't want to use silicone tape as some sites suggest, that just doesn't sound safe.

However, I'm not too sure where to start with the process of replacing it. I can do the anode cap, but the rest (the destination of the other two cables) is a mystery for now. I should have a good clear idea what I'm doing before starting.
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Old 8th Dec 2013, 2:14 pm   #32
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Default Re: Crackling Inside Beovision 7802

Hello,

Here are some pictures from a very similar Beovision 8800 (type 3312) 26" set. Is your TV like this?

Regards,

Dazzlevision
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Old 8th Dec 2013, 2:19 pm   #33
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Default Re: Crackling Inside Beovision 7802

Hi, thank you. These pictures are very similar. The notable parts appear identical, which are the anode cap, the resistor box and the two cables coming out of it. I believe one is for focus and the other I assume is the high voltage supply. My technical problem is not knowing quite where they go and how they're attached.

Last edited by AC/HL; 8th Dec 2013 at 2:25 pm. Reason: Unnecessary quote of the entire previous post removed
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Old 8th Dec 2013, 2:42 pm   #34
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Default Re: Crackling Inside Beovision 7802

If it arcs, the TV set is obviously working, if it wouldn't work at all there wouldn't be any arcing. What are the symptoms?
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Old 8th Dec 2013, 3:21 pm   #35
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Default Re: Crackling Inside Beovision 7802

The EHT cable assembly goes back to the high voltage transformer where it is "held" by turning a sort of locking collar on the transformer itself. The focus feed goes to the focus control. Whether the part you have found from Donberg includes the correct connectors at the ends of the wires is not made clear but they could be removed from the old one.

This problem, apart from the well known dry joints in the IF can, is probaby this series of chassis' worst vice.
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Old 8th Dec 2013, 3:26 pm   #36
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Default Re: Crackling Inside Beovision 7802

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If it arcs, the TV set is obviously working, if it wouldn't work at all there wouldn't be any arcing. What are the symptoms?
Ok, to be clear I mean there's no picture or sound. When I plug it in the set is in standby mode and this seems normal, but when I wake it up with the remote there's an arc from the resistor box to the coating on the back of the tube, then it pauses and does it again. I turned it off pretty fast and tried again a while later, but the same happened again.
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Old 8th Dec 2013, 3:38 pm   #37
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Default Re: Crackling Inside Beovision 7802

Sounds like the EHT cable/resistor assembly has finally broken down then. As a test, you could always try the cable assembly from the other set if you wanted, as far as I recall they are identical unless they did longer or shorter ones for different tube sizes, though electrically they would be identical.
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Old 8th Dec 2013, 3:42 pm   #38
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Default Re: Crackling Inside Beovision 7802

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Originally Posted by bobbyball View Post
The EHT cable assembly goes back to the high voltage transformer where it is "held" by turning a sort of locking collar on the transformer itself. The focus feed goes to the focus control. Whether the part you have found from Donberg includes the correct connectors at the ends of the wires is not made clear but they could be removed from the old one.
Well, that sounds like something I could do. However, can I just check there's no special tools needed? The cables (assuming they have the right plugs) just plug in and and the transformer can be tightened up to hold it?

Also, thank you to you and everyone for the advice. It's helping me form a better idea what is going on here.
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Old 8th Dec 2013, 3:54 pm   #39
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Default Re: Crackling Inside Beovision 7802

No special tools needed, just common sense about working with high voltages.

The cable(s) push down tube(s) in the high voltage transformer and there is a locking assembly at the mouth of the tube which can be turned about 90 degrees to clamp the cable in place.
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Old 8th Dec 2013, 5:48 pm   #40
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Default Re: Crackling Inside Beovision 7802

Thank you, this sounds manageable enough so far. I've sent an order for the EHT cable and will see what happens when it gets here.
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