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Pay someone to service my B&O MX7000

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Lastmarine View Drop Down
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    Posted: 06 Dec 2019 at 11:37pm
Thanks loads that's very helpful.
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John Bennett View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote John Bennett Quote  Post ReplyReply Direct Link To This Post Posted: 06 Dec 2019 at 10:16pm
A higher voltage rating is fine, just watch for the dimensions (although always check that as caps are often smaller than they used to be).

Capacitance... close and never smaller is a fair rule-of-thumb. So 50uF is fine for 47uF. These are supply buffer capacitors rather than part of something like a precision RC oscillator.

The letters will be manufacturer specific. I'd say anything goes for a TV - it'll be things like extended temperature ranges, which you won't need, but do no harm.


http://www.philwip.com -sibling 'fix-off' (I’m losing by miles).
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Lastmarine Quote  Post ReplyReply Direct Link To This Post Posted: 06 Dec 2019 at 8:09pm
Hi Guys.
Just wanted to say that I haven't electricuted myself removing the LOPT LOL. I'm still here, Just awaiting some tools before i take on the work. Haven't heard anything back from the various people I contacted regarding service the B&O. Even tried the Instagram Guy RetroRestorationUK as you suggested RIchard May, but alas no response. I guess he is overcome with work. However after some diliberation I have decided to take on the work myself. After totting up the cost of recapping the boards and the new LOP, it really would have been just to dear to make it worthwhile paying an engineer to service the set also, especially considering postage costs.

I found this excellent post over at the B&O forums which indicates how to service and more imporantly which caps need replacing on the the MX range of sets to illiminate 98% of issues. I've put together a shopping list of parts via Donberg. However I have a couple of questions I was hoping someone with some better knowledge of circuitry might be able to help me with.
https://archivedforum.beoworld.org/forums/t/24571.aspx

Firstly I am unable to find a couple of the exact caps listed on that thread on donberg. Namely C31: 1x 47uF 63V. Could I use a higher voltage or uF as a substitute if the exact same cap cannot be located ie in place of the above 47uf 63v could a 50uf 63v, or 47uf 70v for example be used?

Also can someone help me understand the difference in labelling on caps? for example if I search for a 50uF 50v cap, I am presented with 50V, 50VR, 50VA, 50VH, 50VRHT, 50VARHT. I gather that VA and VR refer to either Axial or Radial ie the alignment of the pins, and obivously V refers to the voltage, but what is VH, VRHT, VARHT etc.

Much thanks for explaing what is probably the most basic of engineering theory. I am really a novice with this.




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Lastmarine View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Lastmarine Quote  Post ReplyReply Direct Link To This Post Posted: 03 Dec 2019 at 9:12am
Cheers for all the info. Replacing that LOPT does look like a job for someone with more experience than me. I'd give it a go but I'd worry a bad solder join on any of those many connections could be a real hazard. Soldering on the Gun board looks a little skillful too which isnt me.
Im sure I can at least get it off the board though
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Post Options Post Options   Thanks (0) Thanks(0)   Quote eggplantUK Quote  Post ReplyReply Direct Link To This Post Posted: 03 Dec 2019 at 12:38am
Originally posted by Lastmarine Lastmarine wrote:

Hi. I have spray duster if that's the same thing?
Compressed air is effectively the same, usually not as high pressure and you have to be a bit more cautious about it freezing and blasting liquid over electronics.  Don't use long blasts and keep it upright.

Originally posted by Lastmarine Lastmarine wrote:

To discharge should I use a decharging rod that's sent to earth somewhere?
God, no!  The TV should be unplugged, not earthed.  Use a HT probe (or the TV tech's old trick, two screwdrivers) clipped to metal on the chassis and shove it under the anode cap.  Just be very careful not to touch anything as you're doing it.  Leave one hand outside the set if you're unsure.  A probe is insanely expensive.

Originally posted by Lastmarine Lastmarine wrote:

I was gonna check first but I wasnt sure if leaving the set unplugged for 24hrs plus, would do that job sufficiently?
Absolutely not.  It's a huge capacitor with the ability to recharge.  It's possible it has a self-discharge and nothing will happen - but it's also possible it isn't functioning.

Originally posted by Lastmarine Lastmarine wrote:

Also how do you even remove the wires?
Unclip the anode cap then pull the neck board off.  Unclip the focus wire on the CRT socket and desolder.

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Lastmarine View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Lastmarine Quote  Post ReplyReply Direct Link To This Post Posted: 02 Dec 2019 at 10:11pm
Also thanks so much for all your help everyone really appreciate it.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Lastmarine Quote  Post ReplyReply Direct Link To This Post Posted: 02 Dec 2019 at 10:05pm
Hi Barry. Not sure on pins in the neck. If theres any way the tube can be salvage I'd definitely be up for it. I hate to see these old CRTs especially quality ones like the B&O go in landfill. Such a shame no one wants to repair them anymore cos of cost. We all know how great CRTs are. I wish the general public could look beyond size and weight of the things.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Lastmarine Quote  Post ReplyReply Direct Link To This Post Posted: 02 Dec 2019 at 10:02pm
Hi. I have spray duster if that's the same thing? The tv is situated in a garden cabin. The room is built with 50mm thick siberian larch and a further 40mm of insulated plasterboard. However there is obviously no central heating so I have electric heaters inside. While they are set to come on at 5 degrees to avoid antifreeze obviously it's not as good as inside the house. I haven't noticed any moisture however it may well be coincidence but obviously the issue has only occured since it's been in the cabin?

My plan going forward was to completely remove the main board and do a proper check over of caps and joints. Especially if this LOPT mentioned by Eggplant turns out to be a fit. I'd like to recap the set anyway.
I wanted to ask you guys advice on removal of the LOPT. I've never removed one. To discharge should I use a decharging rod that's sent to earth somewhere? I dont own one but can buy one. I was gonna check first but I wasnt sure if leaving the set unplugged for 24hrs plus, would do that job sufficiently? Also how do you even remove the wires? I've seen a guide on removal from the tube but there is a second feed going into the gun which looks a fiddle to remove. Can I just unplug the two wires direct from the transformer?

Oh and to answer your other question. No haven't seen any issue with focus. As I said originally, the image and sound seem unaffected and as good as ever. Apart from that slight picture flicker that accompanied the tick sound on random lines of picture when this fault first began. Like a small power surge.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Lastmarine Quote  Post ReplyReply Direct Link To This Post Posted: 02 Dec 2019 at 9:48pm
Oh my that is amazing thanks so much eggplant. I'd have never found that on my own. That could well be a life saver. Even if the issue wasnt related to that it's worth getting the part while its available still. I'll wait to see if it's the correct one.

Edited by Lastmarine - 02 Dec 2019 at 10:03pm
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Post Options Post Options   Thanks (0) Thanks(0)   Quote BarrySlisk Quote  Post ReplyReply Direct Link To This Post Posted: 02 Dec 2019 at 3:16pm
Does anyone know how many pins the neck has? Can the tube be used as a spare for a monitor? Loads of those MX7000's (and MX4000's) in Denmark. 

Edited by BarrySlisk - 02 Dec 2019 at 3:17pm
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Post Options Post Options   Thanks (0) Thanks(0)   Quote tb2000 Quote  Post ReplyReply Direct Link To This Post Posted: 02 Dec 2019 at 2:05pm
It's almost certainly arcing from the lopt as said above. If you've got an air compressor, that's probably better to use that to blow the dust out rather than a brush. Is the room damp in any way? If so then there's the possibility of HV trying to escape from a possibly slightly deteriorated anode cup on the back of the tube. Also, do you notice any problem with the focus of the picture (sharpness of the image) when you've first turned on the TV? If so then you may have a problem with the neck socket (easily replaced). That lopt appears to be of the type that doesn't have the focus or screen voltage controls on it, as such these would be elsewhere (sometimes lopts can start to crack around the focus and screen controls).
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Post Options Post Options   Thanks (0) Thanks(0)   Quote eggplantUK Quote  Post ReplyReply Direct Link To This Post Posted: 02 Dec 2019 at 1:49pm
Donberg still have the LOPT.  I would double check it's correct, though.  Don't forget to discharge the tube before removing the LOPT if you're doing it!


You could ask Alfonso at the Sony Audio Centre in Croydon if he does televisions (don't think he does, but he did do Betamax) or knows of anyone who still does.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Richard May Quote  Post ReplyReply Direct Link To This Post Posted: 02 Dec 2019 at 12:53pm
I'm sending some Commodore branded monitors to Jan Mlotkiewicz in Coventry.


Never used him before but I hear good things so I'm taking the plunge.
videogamevampires.co.uk
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Lastmarine Quote  Post ReplyReply Direct Link To This Post Posted: 02 Dec 2019 at 9:54am
Thanks John. I think it may well be looking like replacing with a spare part is the only solution. I'll remove the board anyway and see if I cane see any other issues. I've heard the cap for the transformer is sometimes at fault.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote John Bennett Quote  Post ReplyReply Direct Link To This Post Posted: 02 Dec 2019 at 9:27am
Inside the transformer is thousands of turns of hair-thin insulated copper wire, to get rectified mains voltage up to 30kV.
Over time the insulation breaks down, so I’d imagine there’s a fair possibility of arcing internally.

Edit: sadly it’s the sort of reason why folk are mad to pay lots of money for old broadcast monitors and TVs sets as they’re full of obsolete components. At least there’s a fair amount of spares around for some arcade monitors.

Edited by John Bennett - 02 Dec 2019 at 9:29am
http://www.philwip.com -sibling 'fix-off' (I’m losing by miles).
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Lastmarine Quote  Post ReplyReply Direct Link To This Post Posted: 02 Dec 2019 at 8:37am
Would u recommend using isopropyl to clean the area in and around the transformer or just wipe away the dust with a dry brush? There is a fair amount of dust in the tele and even a large dead spiders nest

Edited by Lastmarine - 02 Dec 2019 at 8:38am
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Lastmarine Quote  Post ReplyReply Direct Link To This Post Posted: 02 Dec 2019 at 8:35am
Thanks alot Lix. I did worry that if the issue was related to the transformer there would likely be little I could do to fix it. I will certainly try and clean the area once its had some time to discharge. I found this excellent thread on the B&O forums from a while ago which talks through replacing the most likely failed components. No mentioned of the transformer though. Also shame imageshack has removed all the photos. Good idea on the lights off recording. Will try and have a go

https://archivedforum.beoworld.org/forums/t/24571.aspx

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Post Options Post Options   Thanks (0) Thanks(0)   Quote lix Quote  Post ReplyReply Direct Link To This Post Posted: 02 Dec 2019 at 2:15am
That's most likely the line output transformer (the black block with a thick wire connected to the top of the tube) developing a leak of high voltage which is arcing / discharging through its insulated body to something nearby ie. the rest of the circuitry, hence a slight distortion on a picture line when you hear a click.

Generally that is usually game over for that particular component as it'll only get worse if you continue to use it, either the transformer will burnout or it'll kill something in the horizontal scan circuit.

Now personally I have managed to rescue a couple of line output transformers, sometimes it's as easy as giving it a clean with a brush to remove all the accumulated dust. That's a very rare case though. Another one I fixed by wrapping PVC electricians tape around the base of the housing where the thick EHT wire goes into the transformer, once again that's a rare fix.

However some of the transformers I've attempted to fix have just ended building up such a high charge that they've eventually discharged with a massive zap and gone and killed the board. So ideally you'll need to check to make sure it's 100% the transformer, and then source another one, which with a TV like this is probably only going to come from another set. I don't know. Unless B&O have some good spares service going on.

Try turning the lights off and see if you can see where the transformer is arcing from. And yes, give it a day or so to discharge before cleaning it with an artists paintbrush or something similar.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Lastmarine Quote  Post ReplyReply Direct Link To This Post Posted: 01 Dec 2019 at 10:54pm
Ah yes good advice. I have done so and despite it being rather a scary experience I have documented the issue on video.

Definitely seems to be coming from the main motherboard. Particularly the large red thing. I am going to assume that's a large TMR? As you can hear if you watch to the end, a worrying sparking sound suddenly starts up out what appears to be the large black power supply to the right of the TMR which I assume feeds power to the tube. I think perhaps eiher one of those might be the culprit but it could of course be something else. Perhaps you could have a watch and see if anything clicks for you?
I should add thankfully there is no smell of burning or electrical damage coming from the set but I didnt leave it on long as you can see when I panic and switch it to standby.
https://youtu.be/VQpVFonfg2k
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Post Options Post Options   Thanks (0) Thanks(0)   Quote thegreathopper Quote  Post ReplyReply Direct Link To This Post Posted: 01 Dec 2019 at 9:00pm
instead of disconnecting things, first turn on the TV and see if you can see where this buzzing sound is coming from.

Do this with the back off but don't touch anything while doing this. The fault may be obvious.

good luck Smile
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