Crackling Inside Beovision 7802

[bobbyball]

Keep us posted!

[Maarten]

The symptom your set is showing, is called going into protection or hickupping. The arcing is most likely the only cause and there's probably no other damage caused by the arcing.

[Okto1984]

Originally Posted by bobbyball

Keep us posted!

I will, but I think it's going to be a while. Donberg have emailed, and the good news is they can get the EHT cables, but they estimated 20-25 days before they have them. Combined with Christmas post, it could be a while.

I just hope the arcing hasn't fried anything inside the TV!

Originally Posted by Maarten

The symptom your set is showing, is called going into protection or hickupping. The arcing is most likely the only cause and there's probably no other damage caused by the arcing.

That's what I'm hoping. The arcing was going to the aquadag coating and nearby strip that connects the aquadag. I didn't let it arc more than a few times before I realised and pulled out the plug.

[Welsh Anorak]

I wouldn't worry too much - TVs are remarkably resilient to lots of volts flying around.
Glyn

[Okto1984]

I'm still feeling optimistic

Anyway not too much happening yet as the EHT cable isn't here. I'm currently trying to find a complete service manual (only turning up bits here and there so far and no paper copies to buy either), but can hopefully figure it out without if I have to. I looked inside the TV and can see how everything is connected now.

[Freya]

I have a service manual, if you PM me your email I can forward it to you.

[Okto1984]

Hi Stephen, thank you for the kind offer. I'll send a PM in a moment. It should come in useful, I think it will contain instructions for the EHT cable replacement, and maybe something about the power switch too.

[Welsh Anorak]

Hi
Coincidentally I have just been given one of those sets, complete with its odd stand. Guess what? Yes, hiss, trip, hiss, trip... I think I have a new EHT cable somewhere. I'll keep you posted on this one.
I have a customer who still has one in daily use so they are quite a viable set even now.
Glyn

[bobbyball]

Nice sets these, have several of them.

The strange EHT cable is definitely the weakest link though. It will be interesting to see what our friend Okto1984 gets from Donburg Electronics, as without this special cable/focus bleed resistor assembly these sets are essentially scrap. The only similar arrangement I can think of is the Thorn TX10 chassis which uses a similar combined chopper and EHT transformer. This chassis was notorious for it's focus control of course and it's EHT lead is different but the priciple was the same.

[Okto1984]

This cable had me worried at first just because it seems far more specific than the others I was finding. I ended up reading a Danish site with the help of a English-Danish dictionary that is listing the HR1689 code for a number of beovisions (including my 7802), and when I looked for it on the donburg site I found a photo that appeared superficially at least to match perfectly the one I have. So I figured from these two clues that it probably would be the one. Either way, I'll definitely have more to say once it's here.

Meanwhile, I still don't have a full service manual. The one Stephen kindly sent has turned out to be very helpful as it's all the schematics, and in good resolution - which is a big improvement on what I already had. But it's still the first section only. Judging by the chapter titles, the bit that would tell me more about the EHT cable is somewhere else further in. I have found someone selling a German copy. German isn't a language I speak well, but I suspect it will be plainly written and illustrated in places too, so I'm willing to give it a go if nothing else turns up from the other emails I sent out.

[Okto1984]

Well, I finally have a full pdf of the service manual - which was not easily found. It covers the beovision models 8802, 7702, 5502, 9002, 8902 and of course 7802. If anyone would like a copy, let me know.

[Okto1984]

Originally Posted by bobbyball

The strange EHT cable is definitely the weakest link though.

According to the service manual, B&O call it part number 6270209. As it turns out, searching for this finds several places selling the cable I've ordered earlier.

[bobbyball]

B&O manuals are very oddly laid out and, frankly, can be a pain!

I have the full manual for this series of models "somwhere" and I will try and dig it out - I need to do some whork on one of my own sets so there is a double incentive to find it.

Away for the weekend but I will have a look in the week.

[Okto1984]

I have good news. The HR 1689 cable arrived today and I fitted it. It looks much like the original and had all the correct plugs, and I can confirm the TV is working again with a decent picture and sound.

Anyway, I'm really pleased I managed it as this was all new. However, I also had a lot of advice from people here too which has of course been very helpful, and I am very grateful for it too.

As for the TV, it's working well, but I do notice some flickering when it's displaying on screen menus and things with sharp lines. I suspect I need to adjust something, perhaps the focus, but don't want to start changing things until I know more. It's not very noticeable with moving images however, so the set is very usable again.

[bobbyball]

Glad it works so well, and good that this "special" part can still be obtained.

With a set of this age, the electrolytic capacitors will be starting to give trouble and these can be gradually replaced with a bit of time and patience.

[Okto1984]

It is fortunate. Looks like you can still buy the LOPT too.

As for capacitors, I have wondered about them too as they seem to be a candidate for the humming from the speakers. Plus they're pretty old, most of them are Roederstein gold and labelled "made in W. Germany". Seems they're not available now, so I have to pick a replacement.

I have an OK idea what I should do, but I don't know what new capacitors would be good quality and well suited to a TV? Capacitors seem to be one of those things where you can spend as much or as little as you want, but I don't know that I should believe expensive ones are always the best or that cheaper ones are always bad.

Also, I was wondering what is going on with your set that it needs work?

[bobbyball]

Well, capacitors come in all sorts as you say but broadly speaking and with common sense "you gets what you pay for". It's more complicated than that of course as there are many different specifications and you can be sucked into paying silly money for "audiophool" types. What is needed for the power supply circuits is "low ESR" types that are specially designed to work "hard" at high frequencies. Makes such as Panasonic are always a good bet but there are plenty of others.

My set that "needs work" is (are) actually two 20" models that are the "basic remote". These just have an aerial input and the "amp" and "tape" DIN sockets. Fine to use with a modulator but these sets are designed for AV connectivity and I have a spare SCART panel that I am intending to fit to one of them, just need to check in the manual where the various plugs go (or compare it with a set that already has the panel, which I do have although it's elsewhere at the moment). Still need to find the manual!

What I will do before I switch it on is thorougly clean the EHT cap, EHT connector on the tube and surrounding glass, and the ends of the leads that plug into the high voltage transformer.

As for your "hum" on sound, I have not had this on any of my sets before and as you suspect it could be down to poor smoothing on the supply rails or even a lead carrying the audio signal being dressed too near something else. Does it hum at all settings of the volume control or just when it is turned up?

[Okto1984]

Interesting you mention the scart socket. I noticed the service manual has a few pages about fitting that panel (if you can't find yours, or it's different, I can email the pdf). I've also been figuring out what to do with my scart. So far with the devices I have and the available cables, I'm using the scart with composite video and left and right audio, which is giving a good picture. I gave up using the HDMI to composite box because it was the cause of the flickering. I'm getting a much better picture without it, in fact it's a very good bright, steady picture and all the on screen displays and even small text look sharp. The only down side is NTSC DVDs and all blu rays will only play in black and white now. Still, I've got iplayer and PAL DVDs.

There are other outputs from the blu ray player, but the problem I have is that I don't know quite what I can connect to the scart and AV din socket on my TV, it's just not well explained in the manual. I suspect standards have evolved a lot since it was made, and chances are it just made more sense at the time as many of the devices I'm wondering if I can connect today didn't exist then.

As for the sound, it's a steady unchanging humming/buzzing. It doesn't change with the volume, it's even there when the TV is muted and it's present on all channels and AV. I've tried unplugging other devices around the house to see if they're causing it, but no change. Through the TV speakers it's subtle enough to not matter, but through headphones it seems much louder and they're not usable.

I will replace the power supply capacitors soon anyway, so that may solve it. I've found they're all numbered on the board and in the service manual, just need to look at them to confirm their sizes before buying new ones. Some are in fairly tight gaps between other components.

[Michael Maurice]

The capacitors I've had trouble with in the past are on the scan panel which is trhe panel sitting at the bottom of the set.

I use either Panasonic Nichicon or Vishay capacitors which are availasble from RS or Farnell.

[Okto1984]

I haven't thought much about the scan board before. Have they just been troublesome, or specifically a cause of audio buzzing?

Anyway, that's two recommendations for panasonic now, so I'll try to get those. I've had the case off briefly earlier to look some more at the capacitors. There aren't that many electrolytic in the power supply, the most noticeable one that I assume filters the mains as it's in the section marked mains is C7, which seems to be a 220uf 385V capacitor. Should I worry about the other ceramic and plastic ones? I am likely to replace C2 at least, as it's an evox RIFA across the mains type, which I know from owning a few BBC micros tends to abruptly pop and smoke sooner or later when it's old. It's worth doing just to never smell that smell again!

I also took the chance while it was open to let it warm up for about 40 minutes then adjust the focus, which seemed a little out with the new EHT cable. It's a really nice picture now.

Also looks like someone has repaired the board before, a few solder joints look different, slightly heavier solder on them and some left over flux while the rest of the board is spotless. The LOPT has either been replaced or resoldered, and R11 and something next to it called the PTC too - but I have no idea what a PTC is.

Just a quick addition: I now think C7 is the mains smoothing capacitor as it's straight after the bridge rectifier.