Crackling Inside Beovision 7802

[bobbyball]

Well done with your replacement capacitor.
Based on the effect replacing just one of the old capacitors has had, further replacements in similar areas should improve the performance still. Just take it slowly and carefully, and along the way you are learning as well...

[Okto1984]

You're right, slowly is the best way for me with this. What I don't want to do is put in a whole lot of new capacitors, then find the set doesn't work or develops a problem and not know where to track it down.

As for learning, I'm glad I put my question up here, as although I'm not adverse to trying things out and looking stuff up, I really doubt I'd have got this far without the advice I've received. It's just not a topic explained anywhere else I've found at the right level for a beginner.

Meanwhile, there's still a few things to do in time. Mainly figure out why the tweeters don't work (I suspect a filter circuit inside the resin speaker boxes), and the mystery buzzing, as well as the stuck power switch. However, for now I'm just sticking to slowly replacing the capacitors which I suspect are getting tired and dried out from age.

[bobbyball]

The stuck power switch is commonplace on this chassis. As I recall the switch was a "special" but I think there are probably replacement types that will fit. As for the crossover network for the speakers I can't remember where that is, and I don't think it's inside the speaker boxes but until I locate my copy of the manual I can't say!

[Okto1984]

As it's lower down the to-do list, I haven't spent too much time looking for the crossover yet. However, it looks like two wires go in to each speaker box, and a further two leave to connect the tweeter above. Haven't opened one up, but that's my next step. The schematic shows a pretty simple crossover, just a couple of coils and one non-polar capacitor for each speaker assembly.

I have also found a couple of places selling the original switch, but they're about £20 - and postage from abroad might be high. That, combined with the original switches being a common fault, is making me wonder about an alternative that fits. Not too sure how to search for that however.

Meanwhile, things are going well with the TV, but slowly as I've been busy. I replaced the big mains filter capacitor. It works well and I also found the picture more stable. Previously, particularly on bright pictures I could see the screen flicker a little. Now it looks perfectly steady, which is great. But the audio still buzzes... Oh well.

[Okto1984]

It's been a little while since I've updated, but things are going well. Almost all the electrolytic capacitors on the primary and secondary side of the power supply have been replaced now. Mostly with Panasonic FR capacitors.

Although I was always happy with the picture, the quality has improved. It's genuinely surprising how good it is and compares well even to new HD sets of a similar size.

Still got the buzzing in the audio, but puzzlingly, it's fainter now. I kind of suspect the flyback transformer, I thinks that's what I can hear it buzzing from inside the TV, and it's the same frequency of buzzing from the audio. If I listen between the grill on the top and the speakers, the two merge perfectly.

[Welsh Anorak]

Hi
I'd be more inclined to suspect the scan coils as they happily buzz at 50Hz. Or possibly a choke on the mains input as you've obviously had to disturb them during your capacitor marathon.
Glyn

[Okto1984]

Hi Glyn, thank you for suggesting this, as I'd never thought about these before. I will have to investigate the choke further. However, I'm not sure how could it make the audio buzz? Well, I understand their producing a magnetic field that can cause interference with the audio, but not why they would now being do this or how to stop them doing it. My googling hasn't found anything about this, although I do know a lot more about coils now.

[bobbyball]

Good that it has improved so much with your capacitor changing marathon. These sets when working properly produce amongst the best pictures of all time.

I can't work out your audio fault, never had it on any similar sets of mine. I can only assume the 50Hz buzz is getting into the audio circuits somehow, perhaps via a faulty decoupling capacitor...

[Okto1984]

It's a very subtle buzzing when using the speakers, from about a meter or more away you'd not really notice it. It's only when I attach headphones that it is very noticeable, so it's possible many people have this buzzing and don't know as they're not using headphones.

I'm still working on the set and may discover the cause in time, and will update here if I do. In the short term, there's three remaining capacitors on the power supply to change. The ones replaced so far seem to have helped in various ways, the picture is a little sharper, the refresh is hardly visible (after the big mains filter cap replacement) and the power supply is buzzing much less. I'm curious to see if these last few do anything else.

I may move over to the amplifier board next as I've had record players of similar age recapped before with great results, but not sure which capacitors would be best there. In the power supply I've been using Panasonic FR for anything under 63V and a couple of high ripple current/low esr Vishay capacitors for higher voltages, both types seem to be well regarded for SMPS, but not for audio uses.

[Okto1984]

Interestingly, this thread scores highly in the search results on google for many things to do with repairing a beovision 7802, so perhaps it will help other people. I'm going to add useful things I find here as a simple way to share the details and to help me remember when and where I found things.

I've found a useful resource for vintage capacitor datasheets (www.datasheetarchive.com), and have identified the original capacitors in some locations and found their values, as well as suitable replacements. I'm still certainly an amateur, so always check things, but it could save other people restoring this, or one of the similar sets like the 7702 or 8902 some searching as I didn't find all of these things very quickly.

C7 on board 6 - the primary power supply, on my set has a 220uf 385V Roederstein EYV 35x50mm. A big ROE gold cap with four pins, two of which are just for mounting as it's a heavy cap. Found it on page 5 here (http://www.datasheetarchive.com/dl/D...SA00264092.pdf). Fortunately, Vishay who bought Roederstein some years ago still make four pin capacitors like this, and their 052 range contains one with the exact same values and size (http://www.vishay.com/docs/28345/050-052ped-pw.pdf). The new one is blue, but I suspect it's the same product inside as the exact values for everything listed all matching would otherwise be kind of uncanny. Whatever the case, it's been in and working well for several weeks now.

Board 42, the AF amplifier contains some curious Roederstein EDG caps - they have metal outer cans which have three terminals to the PCB and then one terminal in the centre. So, the outside of the can is it seems part of the circuit (http://www.datasheetarchive.com/dl/S...IH00244457.pdf). Turns out Vishay still make them (called mounting ring), and have the 2200uf 25V and 2200uf 63v versions needed, but finding anyone who sells them hasn't turned up anything yet.

The set also contains various blue Philips axial capacitors, from the 030, 031 and 032 range which I found here (http://www.datasheetarchive.com/dl/S...IH00025180.pdf). Where I have 40v or 50v version called for in the service manual, they've actually fitted 63v versions. Possibly just what was available or it was cheaper per unit to buy them all the same in bulk, or maybe it was on purpose? Well, I'm going to match the 63v version's properties when I replace them to be sure.

There's also a number of radial ROE EK 470uf capacitors, little red cylinders. Everyone seems to know what they are, but no datasheets yet.

It's been interesting to look at the datasheets as general browsing audio/video repair sites suggests that modern capacitors are almost inevitably going to be better than ones from the early 80s, but the datasheets I've found suggest this isn't true here - they compare fairly well. It's also worth noting B&O were using long life capacitors for all I've looked up so far. I'm going to be more careful with replacements after seeing this and not assume new is always better.

[Maarten]

Any Vishay capacitor range designated by 3 numbers isn't a former Roederstein range but a former Philips range, which is at least as good or possibly better.

Thanks for pointing out newer isn't always better!

I mainly use Panasonic long life / low impedance / high ripple capacitors since they tend to be cheaper than similar Vishay or Epcos capacitors, but I'll make sure to do some more comparison of specs next time.

[Okto1984]

Hi Maarten,

That's useful to know about the numbers. Through that, I've since found a datasheet which shows some of the Philips and Roedestein products which are discontinued and the suitable replacements they now make (http://www.datasheetarchive.com/dl/D...SA00433742.pdf). It's pretty relevant to many of the caps I'm finding in my set.

I've also been using Panasonic caps, mostly FR range as they're cheap, claim to last a long time and have better ESR/ripple than most anything else I've looked at and come in many uf and V ratings. But they're all radial, and this set does have some axial ones. Fortunately, unsoldering many of the little ones discovered extra mounting holes which allow radial caps to be installed in replacement. However, the big axial capacitors need axial replacements, and the most suited I found are from Vishay. So I am using some of both.

As for the TV, the sound still needs work. Picked up a bit with the new audio power supply cap, but it didn't last. Some sounds come through surprisingly bright and clear, other bits kind of weak (voices are the worst sometimes), as if there's a kind of unintended filtering going on. It's not terrible, but I know this set can sound a lot better than it does. I am however still getting a great picture, and will be recapping the preamp board when I get some time. May even find the source of the buzzing...

[Okto1984]

Just a small update - I fixed the tweeters by replacing the crossover capacitors.

They're located in the resin speaker boxes, which unlike most other parts of this set are rather hard to remove and require a fair bit of disassembling the rest of the set.

The crossover capacitors are soldered to a small circuit and their leads pushed in to a piece of fiberboard. I installed some film capacitors, Vishay 1839 as I found positive recommendations for them online for this use. They're also inexpensive. The tweeters are definitely working again and it sounds very good now.

Meanwhile, the EHT cable I ordered (HR 1689) from Donberg right at the beginning of this, which a few people were curious about, has been tested for many hours now and is still working perfectly.

[DAVE123]

Hi, i also have recently acquired one of these sets and I agree, they're great for age. One trivial thing is bothering me though. When i connect a SCART source, does the TV automatically detect it, or do I need to select a setting on the remote? I've tried everything but to no avail. Apologies for hijacking the post, but it seemed a relevant place to ask

[DAVE123]

Okto1984 - could i ask where you found the on/off switch as mine has the same problem too.

[gec2110]

The TV should auto detect, not sure if it was with pin 8 or 12, providing you are using a full SCART.

[DAVE123]

Have now managed to work out that the SCART is on channel 0, but with a dodgy remote this is pretty difficult to select. Thanks for your reply, gec2110 Still not been able to find a replacement on / off switch yet though.

[Okto1984]

Hi DAVE123,

No worries, you're not hijacking the thread. It makes perfect sense to ask someone who owns the set.

My set automatically selects the scart input, but it only is a stable picture on certain channels. 0 is one of them. Channel 33 also works, and might be easier to select on your remote? Remotes for these are easy to find on ebay for not too much money last time I looked. However, your comments about it being difficult to select with the remote make me wonder, have you found the fold out door below the power switch? I guess if someone didn't know to look for it they might not realise it's there. If you gently push the speaker section below the power switch it goes in a little and then pops out to reveal a control panel, from which you can select channel and other things like tuning.

As for the power switch, I'll investigate that and post back soon. The switch type I used has been a good replacement in both my beovision 7802 and 9000, but isn't an exact drop in, it does need some minor modifications to enlarge the switch's mounting holes.

[Okto1984]

This is the switch I used, I bought it from conrad-electronic.co.uk

http://www.conrad-electronic.co.uk/c...HA-latch-1-pcs

It's very similar to the original, but not quite exact as there's two differences.

First, It has some pins on the bottom, which you cannot see in the picture. I clipped these off, leaving just the tabs on the top to solder the wires to.

Second, the metal mounting plate holes don't line up perfectly with the mounting screws in the set. I had to slightly enlarge the mounting holes on the switch, then fix it to the holes in the TV case with a couple of small nuts and bolts. The result is solid and it's not going anywhere.

Overall, I'm happy with the switches. The switch fits the space and connects with the plastic button on the front of the set perfectly. They needed some adjustments to fit, but only to the switches, not the TV case, and have been in and working well for some time now. I did at the time find a place selling exact replacements for about £25 each, but that was far out of budget!

As for the TV, it has really been worth repairing. It has excellent picture and sound when using the scart socket, and making some adjustments with the focus also helped. So far it seems reliable since the repairs, many of which I did after receiving advice here. I'd estimate it's been running about ~200 hours the past year without problems (we're quite big TV watchers, at least 3 hours week), but our one has had a fair bit of work done. Hopefully now we'll get plenty more use out of it. However, our older, but better cared for beovision 9000 in the sitting room, which for many years has been used for just one or two films a month is still going in almost completely original condition, so I suppose how much if anything might need doing depends on the set. This 7802 was in poor condition when we got it. It worked, but was hanging on right at the point where it was about to give up. The EHT cable was sizzling, the LOPT had cracks in the solder joints, some of the capacitors had green stains around their pins from leaking, and the power switch only lasted a matter of weeks before it stuck. In hindsight, our positive experiences with the 9000 were based on it being cared for better and lightly used, and just buying and expecting another set from 1983 to work was optimistic. Everything proved fixable in the end however, but I mostly stuck it out as I didn't want one of the newer beovisions with a tinted glass screen over the CRT.

[Nickthedentist]

Originally Posted by Okto1984

...we're quite big TV watchers, at least 3 hours week...

4 hours a day is average for the great British public, allegedly