ARCHIVED FORUM -- March 2012 to February 2022READ ONLY FORUM
This is the second Archived Forum which was active between 1st March 2012 and 23rd February 2022
Hi all. Further to our introductory thread in the vintage area of the forum, we have a later model Beovision 8802 which we rescued from a friend's damp shed a couple of weeks back.
I've just got stuck in properly with it as I managed to find a genuine factory service manual which I promptly bought and it arrived today.
The set initially had multiple symptoms of very jumpy (but not rolling) vertical and extremely tweaky horizontal, a flaky main power switch and no sound at all... The picture issues have now been fairly well resolved with no more than a clean and wiggle of some dirty pots, the power switch was pretty well dead, had been arcing internally and a spring was broken so it's hardwired on for the moment while I locate a suitable replacement.
The prevailing issue then, is one of no sound. I did get a little crackle from the speaker when powering up with no signal but only the once so far. There's no response at all when rotating the volume/bass/treble pots nor when operating the volume on the 'video terminal' remote so I'm leaning toward a bad connection to/on the AF amp board.
Just wondering if there's any common issues with the sound before I assume corrosion is all? (EDIT) Oh, and also wondering what the consensus is on the electrolytics in B&O kit of this age? Generally reliable/worth changing the higher voltage ones or recap the lot? (they do look to be of high quality, but I'm aware that means little with electrolytics as they start to age so just looking to be safe with it)
Cheers, Dan.
I think the sound is muted when no signal is present?Do you have an external source connected,eg digibox,dvd etc,via the Scart etc socket?
There were several variants of this set.Early versions had manual presets for the tuning,then later versions were more sophisticated and employed digital tuning.
The AV switching became more convoluted later,with multiple connection facilities available.Does your version have a Scart socket or 6 pin Din for AV.
The TDA2020 audio output chip was a common failing.
The electrolytics here are quite long lived,But it would be prudent to replace those in the power supply,particularly those in the primary stage.
Nick
Yes got a DVD playing via scart (it's a later set) and on further checking I think the output stage is working. At least as far as I can get a crackle when inserting/removing a headphone jack, and I can hear a faint hiss when the volume's turned up.
The pots on the DA board have come back with a bit of a lube and wiggle, and I've also noticed when/if I touch the pot's pins while powered up I can increase the hiss when it couples to ground via my body (presumably).
My thoughts at the moment are, when I get a moment, I'll look into whether the audio is seeing any input since I feel like the issue is further back.
(I think this set might have a TDA2040 but not sure, still a bit brain-addled as been working on a couple of Volvo stereo head units earlier too and the kids are almost as loud as those!) :D
Thanks for the advice on the caps, kind of echoes my thinking. Cheers, Dan.
Curiously,the audio signal routing is not shown in the manual for the mono version tv,and it does seem as though the signal in your tv is getting lost somewhere in the av switching for the Scart socket.
As you can see from the manual,there were many variants and module options too.
You should be able to "blip" the input to the main amplifier(yes indeed TDA2040) by touching pin 7 at connector P14,and hear a buzz from the speaker if the chip etc are ok.
Other than that it means signal tracing (without a circuit!!)around the av switching stage.
I'll keep digging!
Thanks, just to confirm it is a TDA2040 chip. I've yet to source a decent RF signal of any sort, so can't say for sure if it's just AV that has no sound or both. Ideally the next step would be with a signal generator with a probe to inject IF or get an oscilloscope on the input to see if it's seeing any sort of signal/where the signal drops out and work back until something shows it's head.
Sadly I have neither of these essential bits of kit at the moment as I'm only starting to get into this as a hobby recently. I'll be on the look out for an old 'scope first of all I think, since this would also be useful in my other hobbies working on cars (I've managed with a multimeter and intuition until now but it'd be useful), unless you'd advise otherwise. Which tool would you think most useful tracing the audio, 'scope or signal generator?
Thank you for the help, it's much appreciated.
"blipping" the various points of the audio route by touching with a finger,is a crude form of signal injection,and you should be able to do this all the way back to the Scart socket.This will largely excuse the output stage if successful.
An oscilloscope has to be the most versatile piece of kit to invest in if you intend to do more work of this type.They are much cheaper(and smaller) these day's,and I'm sure you could find one via that well known auction site etc.
Do you have an old vcr somewhere perhaps?This would have an analogue rf (coax)signal output that you could tune the '8802 tv to ascertain whether the sound problem is just affecting the av input?
It will need to be an old analogue vcr,as the later digital (DVB)versions didn't incorporate modulators in the rf output.
Sadly no, don't even have a VCR any more :( it's something I intend to rectify soon though but for now the old pinkie will have to suffice as signal generator.
Glad I seem to be on the right track with thinking of a 'scope, it would be very useful for a lot of things I reckon. It'll have to wait for the moment though as I need to spend my next bit of "spare" cash on a new clutch master cylinder for our Volvo. Typically, it's started showing it's age by flipping the seals the day before a long journey! Fortunately I managed to flip them back but here's hoping they hold out until I can replace it in the next week or so...
Well we managed our trip without any problems & are back home now. Had a further play with the TV last night and so far have ascertained the amplifier is working as it should, the DA board is fine and the pots on that are functioning despite the treble control being a little crusty still. And there's continuity, at least, from DA back to the pre-amp although very little in the way of signal output from it, at least that can be detected with a DMM.
So now it's pretty much a case I think of waiting till I get my hands on a scope (would like a signal generator as well) to determine more accurately what's going on since I imagine the voltages/current from pre-amp to main amp would be nigh on impossible to verify on a DMM display. Other than this it'd be a guessing game I suppose, but I was thinking maybe I could inject some sort of signal into the pre-amp and see if there's anything getting through it. Unsure of the levels it'd usually work at but my thoughts currently (no pun intended) is that the few mA and mV that an Ipod or similar would put out from it's headphone socket ought not to do any harm at least? Or maybe even the output of a DVD player scart lead (which I measured to be around 150mV max on my multimeter, using the opening scenes of Terminator 2 as the test)
So if I experience an uncharacteristic bout of saintly patience I shall be waiting until I have the proper equipment before I continue troubleshooting the sound, but otherwise will attempt to stimulate the pre-amp (And knowing how impatient I can be, possibly also removing the relevant transistor and testing it out of circuit.)
For the moment if anyone knows (even roughly) the sort of input levels one would expect into the pre-amp and/or main amp that would be useful to know, if only to save overdriving the living snot out of either of them with my headphone idea!
Hi Nick, just seen your email and replied. Thanks, that convertor could be helpful with more than just fixing this TV.
Also, on re-reading your last post I have a sneaking suspicion I've inadvertently found the problem without even noticing, since touching the connectors from the DA board to the amplifier creates a fairly loud buzz which varies nice and smoothly with the volume pot and/or volume buttons on the video terminal (suggests to me the amp and volume pot at least are working fine) but then touching a point between pre-amp to the DA board (even right on the DA input) produces barely a crackle.
This is me typing while quite distracted and tired but I think maybe it could be a problem on the digital/analogue board or one of the tone pots. Would make sense too given that this & the power switch are the main areas of moisture damage. Will have to re-read these posts and re-recheck my "test" points when the kids are back in school and I've got a bit more time to think logically about it but it wouldn't surprise me if your advice had led me straight to the issue.
Cheers again, Dan.
Well, today I had a surprise. Doorbell rang and it was a parcel... "I've not ordered anything?" thinks I...
Certainly wasn't expecting a scart/RF convertor to turn up so quickly, let alone a spare (much cleaner) video terminal remote also! Thank You very much indeed Nick & I shall get on paypal Tuesday when I get paid. I guess the battery covers breaking/falling off on the video terminal must be a common failure since I've not seen one with the cover in place yet.
Not had a chance to play with the convertor yet but I'll try and give it a go later on hopefully & then we'll at least know whether the sound is getting lost in the AV/scart input side or further up the line. I do have a suspicion though that it could be on the DA board. I hope it is anyway, that would be a nice easy repair whatever it is that had failed on it.
Thanks again. I'll update what I find when time allows me to test further.