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 Post subject: Bang & Olufsen MX7000 CRT - No Power
PostPosted: Thu Nov 22, 2018 9:12 pm 



Joined: 17 Sep 2018
Posts: 31
Hi Guys,

I just picked up this lovely CRT recently for next to nothing but it wont currently switch on and I see no red standby light at all. It has a 2 pin Euro plug on the end of the cable which I have plugged into an adapter (I am in the UK so a 3 pin adapter) and the TV is rated for 240V AC.

I assume the fuse would be a good place to start, does anyone have any experiences of the MX range for things I could look out for?

I am fully aware of the high voltage dangers of working on CRT's so am hoping this might be an easy fix.


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 Post subject: Re: Bang & Olufsen MX7000 CRT - No Power
PostPosted: Fri Jan 11, 2019 12:21 am 



Joined: 17 Sep 2018
Posts: 31
Ok an update....


I spent some time doing lots of research into the common faults and testing components on the board and found a failed TR33 (BU2508DF) transistor. I couldn't find any dry joints or anything like that but i replaced the following components in the circuit.

TR33, C100, C101, C102, C103, C104, C105, C106, & D82.

So after replacing them.... Success! Red standby light came up and the TV switched on. I was feeling quite proud of myself at this point but alas it wasn't to last.... 5 minutes later it switched itself off and went back to standby :cry:

The TV now has the red standby light but wont come out of standby the green power led lights up for a second and then goes off again. However if I leave it unplugged for a little while it will turn back on again for a few minutes and then goes off again.

I found the service manual / wiring diagrams for the MX6000 model (which is essentially the same TV minus the active speaker system) here http://beomanuals.com/manuals/Beovision ... 0,6000.pdf


I am sending out a cry for help for anyone who has experience with these models that might be able to help me! I am so close to getting this going again.


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 Post subject: Re: Bang & Olufsen MX7000 CRT - No Power
PostPosted: Sun Feb 03, 2019 10:12 pm 



Joined: 17 Sep 2018
Posts: 31
UPDATE:

I came to conclusion after much investigation and swapping capacitors that it was likely to be the high voltage transformer and I was not able to find a replacement for it.

Not all was lost though I picked up another MX7000 (SW1.0) in excellent condition with the motorized stand for about £40... It had been sitting for 5 years unused but powered up fine, it did switch off after about 20 mins and went back to standby mode. However this was a different error (Powerfail) and in my investigations i ended up mixing the mainboard from this set with the other boards from the original one and now have a fully working set... and whats nice is I am able to enter service mode with the remote etc (this must have something to do with the AV switching board that came from the SW4.7 set.

I have given the other set to an electronics guy i met recently (friend of a friend) to get a 2nd opinion on it to see if it is indeed the high voltage transformer or if it is still repairable.


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 Post subject: Re: Bang & Olufsen MX7000 CRT - No Power
PostPosted: Mon Feb 04, 2019 11:18 am 



Joined: 06 Mar 2017
Posts: 93
Which version was your first set? I bought replacement parts (complete boards) for a MX7000 once through a Polish website. Maybe they can also hook you up with a flyback transformer. I wouldn't look for one until you are absolutely sure that's the problem though. I have 2 identical MX7000's, which makes troubleshooting a lot easier, because I can just switch boards and parts and pinpoint the fault.

Anyway, glad you got a replacement set.


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 Post subject: Re: Bang & Olufsen MX7000 CRT - No Power
PostPosted: Mon Feb 04, 2019 12:08 pm 



Joined: 17 Sep 2018
Posts: 31
Makinx wrote:
Which version was your first set? I bought replacement parts (complete boards) for a MX7000 once through a Polish website. Maybe they can also hook you up with a flyback transformer. I wouldn't look for one until you are absolutely sure that's the problem though. I have 2 identical MX7000's, which makes troubleshooting a lot easier, because I can just switch boards and parts and pinpoint the fault.

Anyway, glad you got a replacement set.


Hi, the original set was a SW4.7 and the replacement was SW1.0 (in much better condition than the later 4.7 though).

The issue is 100% on the mainboard (PCB4) on the original set as currently all 4.7 boards (AV switching, teletext, main processor etc etc.) are working with the 1.0 PCB4 sitting inside the 1.0 shell (which houses the speakers amps, the tube, outer plastic etc) if that makes sense? I also had it all running like this in the original 4.7 shell for a bit, so the only swapped component was the PCB4 from the 1.0 everything else in the 4.7 was running fine.

When I did have it working for a bit it was showing error code 8C which i believe is "13IC2 Deflection controller" but it would only stay on for a few minutes at a time and eventually it gave up doing this, and eventually progressed to a couple of bangs and sparks!

I have been over the original 4.7 PCB with a fine toothcomb and replaced most capacitors, been over the wiring diagram testing all the components with the meter (desoldering to check if i needed to). Other than the blown TR33 I found initially I did find a couple of dry joints on R2 and C2 (to do with the degauss circuit) which I fixed up but other than that it is a bit of a mystery still which is why I think it still points at the transformer.

It is a bit hard to explain the series of events but I have another thread open on the B&O workshop forum which goes into a little bit more detail here https://forum.beoworld.org/forums/t/35992.aspx

At this stage I am not sure I am up for swapping Transformers to confirm though ! Hence me handing it off for someone else to take a look.

I would be interested if you could let me know who the supplier was though?


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