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B&O Beovision 8802 (chassis 7130) - no sound...   Goto page 1, 2  Next  
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bikermack



Joined: 29 May 2009
Posts: 23
Location: Crewe

PostPosted: Tue Aug 14, 2018 10:21 am    Post subject: B&O Beovision 8802 (chassis 7130) - no sound... Reply with quote

So, as mentioned in the title it's an unusual one. I've just rescued a c.1983 Bang & Olufsen Beovision 8802, if anyone even knows what that is since I gather it's a rather rare set. Being in the region of UK 600 when new, I can see why too as it's rather top-end...

Anyway, just wondering if anyone could help with where I might find a schematic for it?

At the moment it powers on but has a problem with vert. stability (it doesn't roll so much as it jumps/flicks about, when it stays put the raster looks clean and square) and there's no sound either.

There's evidence the HOT has been changed in the past and the solder joints look OK, also on the Horiz. board there's a combined resistor and PTC thermistor that has also been changed previously. Other than this I haven't noticed other repair work although I haven't got deep in there yet.

Cheers all, on the (far, far) off chance anyone knows anything about these sets.


Last edited by bikermack on Sun Dec 02, 2018 11:36 am; edited 1 time in total
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JTS1957



Joined: 21 Jan 2009
Posts: 2393
Location: Far, Far Away

PostPosted: Tue Aug 14, 2018 10:39 am    Post subject: Reply with quote

HERE
bikermack



Joined: 29 May 2009
Posts: 23
Location: Crewe

PostPosted: Wed Aug 15, 2018 7:57 am    Post subject: Reply with quote

You, sir, are a bona-fide star! Thank you very much indeed. Will have a look through that now & see what I can do.

I did have a little poke around last night, the power switch is crocked from the damp & had to be bypassed for now & the volume/bass etc pots in the module below that are crusty so might be reason for the sound being dead. Not a huge amount of dirt inside though and the neck of the tube suggests either low hours or replacement tube as it's like new in there visually at least. Off to chase down the vert issue and sound I go. Thanks again, really wasn't expecting to see any reply to this let alone so quickly!
bikermack



Joined: 29 May 2009
Posts: 23
Location: Crewe

PostPosted: Sun Dec 02, 2018 11:48 am    Post subject: Reply with quote

OK been a while since I got a good look at this set. Current situation is we have good picture (vertical issue was a dirty pot) and apart from the power switch it's in good shape.

The prevailing issue though has been with the sound, or lack thereof, through any input.

So far I've ruled out the amplifier & it's TDA2040 IC, and have tested as far back as the TBA120U IC, which I believe is an IF amp/FM demodulator/AF pre-amp. At this point, all voltages around the chip seem good and everything forward of it's output pins is very much awake. Any attempt to stimulate it's input though draws silence.

So, I'm fairly sure this chip has failed & ready to order a new one, just wondering if this chip is known for failure much since I know the 8802's AF amp was originally specced with a TDA2020 which was known to fail & later models used the TDA2040.

If the TBA120U is in fact failure prone then I'd possibly be interested in subbing it with a compatible 14 pin DIP item.

Mainly posting for my own reference too, so no worries if nobody has suggestions thanks Smile


Last edited by bikermack on Sun Dec 16, 2018 7:43 am; edited 1 time in total
bikermack



Joined: 29 May 2009
Posts: 23
Location: Crewe

PostPosted: Sun Dec 16, 2018 7:41 am    Post subject: Reply with quote

Follow up to the follow-up, TBA120U replaced and sound is back. It could have been a cracked trace since one of the pads lifted only too readily on removal but equally that could have been my bad.
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bikermack



Joined: 29 May 2009
Posts: 23
Location: Crewe

PostPosted: Wed Dec 19, 2018 2:43 pm    Post subject: Reply with quote

Another small update, since the sound fix I've been pressing the set into use with a Sega Mega Drive (Genesis)... Anyway, after running for a couple of hours white smoke began to billow from the vents and, lo & behold, the across the line cap has started to short. (on removal, it's reading 0.8 Meg)

Managed to unplug it within a few seconds of noticing smoke, picture and sound were still good as I pulled the plug & I've got a few new caps on the way now. Throwing caution to the wind, I'm just replacing the one that blew plus a couple of others with 250v across them that have started to discolour and bulge (they measured about 30Meg) & none of the 'lytics since they've been behaving well and running cool.

It's a trio of RIFA metallized paper caps that were the sick ones, the Roe "Elco" electrolytics *appear* to be holding up well with age but suffice to say the set will not be running unattended so oughtn't be a major worry.

Fingers crossed I can have it back up before Christmas as it was great fun playing Sonic! Gotta love the smell of roasty caps lol
bikermack



Joined: 29 May 2009
Posts: 23
Location: Crewe

PostPosted: Sat Dec 22, 2018 9:13 am    Post subject: Reply with quote

Right, I have a question now. Just replaced the across the line cap with a like-for-like 0.1uF X2 and a couple of cracked and bulged 4.7nF whilst in there (not like for like, original was metallized paper and replacements are Y2 discs of the same AC voltage rating), fired up the set again and we have no raster & what I can only guess from initial checks, very little HV...

Everything seems awake, sound, deflection circuits, CRT filaments but no raster. What suggested to me the HV was down was the lack of static when I switched on, since I don't have a probe I then popped the cap off and can barely draw 2mm of sickly-weak looking arc on lifting the anode away from the tube.

What could have caused this does anyone think? I had a good picture when I shut the set down with the blowing cap, and all I've done is replace the 3 caps mentioned plus re-flow the HOT... Classic mistake there I guess, more than one change in between testing lol but could killing/dry jointing the HOT drop the HV low? (I've since re-installed the original 4.7nF caps to see if they were an issue, no difference).... I'm estimating it's under 2kV from my crude test.

Go easy on me please lol my head isn't really in gear today (hence my reflowing the HOT when it was known to work just a bit ugly) so I may be missing something obvious. Cheers, will maybe edit the post when my brain engages and I figure what I've done.
JTS1957



Joined: 21 Jan 2009
Posts: 2393
Location: Far, Far Away

PostPosted: Sat Dec 22, 2018 1:39 pm    Post subject: Reply with quote

TR3 (HOT) condition?
bikermack



Joined: 29 May 2009
Posts: 23
Location: Crewe

PostPosted: Mon Dec 24, 2018 5:49 am    Post subject: Reply with quote

Yes that's my thinking. It was known to be working just the solder joints were a bit ugly and blobby. In the absence of proper equipment for this side of things (still have no scope either Sad ) and given the work just done I think I have either dry jointed or otherwise taken out the HOT in trying to tidy up the joints.

I wonder how likely it is I could have killed the HOT reflowing it, I had my soldering station at 310c and only spent a couple of seconds on each leg :/

Been busy playing with Game Gear consoles so not looked at the set since, thanks for the pointer though I think you're right. Will post back when I've either replaced/re-reflowed the HOT or maybe even got a scope for Christmas lol I wish! Thank You & wishing you a good Christmas.
JTS1957



Joined: 21 Jan 2009
Posts: 2393
Location: Far, Far Away

PostPosted: Mon Dec 24, 2018 6:49 am    Post subject: Reply with quote

Resoldering shouldn't be cause (unless you were trying with TV On).

https://vetco.net/blog/test-a-transistor-with-a-multimeter/2017-05-04-12-25-37-0700

Since I don't see a type number in manual, I'll assume it is as drawn on schematic - a NPN bipolar.

NOTE: even before Step #1 blog indicates removing transistor for best accuracy.
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