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MX7000 TV gone to meet its maker

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geearr
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geearr posted on Fri, Jun 1 2012 7:27 AM

Hi everyone

 

After 13 years of a perfectly reliable and high quality life, my MX7000 has finally showed the signs of reaching old age.  During a recent viewing session there was a strong pungent burning smell and the TV was quickly switched off.  When I switched back on later to test the situation, the screen now shows a single vertical white line down the middle and nothing else.  Response to the Beo4 is OK and the sound is still working.  It has now been switched off and it will stay off until I get some idea of what to do????

 

The situation is very simple, the set has next to zero value but it is cosmetically in perfect condition.  I have other TVs that I use so there is no necessity at all to fix it – only sentimental value and a desire to preserve life if there is still hope.

 

Question – is this a case for the quick visit to the local dump or is there a possibility for a relatively simple fix.  What is likely to be the fault?  Can the MX experts advise?

 

Regards

 

Geoff

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solderon29
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This is a common problem with this chassis,and is easily sorted if you can solder,and you are competant with the innards of telly's?There is  a thread on the site relating to this,where a member took some photo's too.

Nick

tournedos
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The old thread Nick refers to is probably this:

http://archivedforum.beoworld.org/forums/t/10557.aspx

You'll need to adapt the information a bit, as the thread talks about the Unity 1 chassis, while MX6000/7000 are Unity 2. They are very similar though, and you can easily follow it with the MX6000 service manual (the good one we have is easiest to find under MX4002).

You have now a horizontal deflection fault, which may have been triggered by a bad solder somewhere or a typical failed cap / semiconductor. Probably very cheap to repair, but may take a while to faultfind.

--mika

Dennis
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tournedos:

The old thread Nick refers to is probably this:

http://archivedforum.beoworld.org/forums/t/10557.aspx

You'll need to adapt the information a bit, as the thread talks about the Unity 1 chassis, while MX6000/7000 are Unity 2. They are very similar though, and you can easily follow it with the MX6000 service manual (the good one we have is easiest to find under MX4002).

You have now a horizontal deflection fault, which may have been triggered by a bad solder somewhere or a typical failed cap / semiconductor. Probably very cheap to repair, but may take a while to faultfind.

There is also a thread for MX4000, MX6000, MX7000 and AV9000. Smile

Take a look here

 

- Dennis

 

geearr
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Thanks very much for the fast replies – much appreciated.

 

I had already found Die Bogenars workshop on the MX5500 and noted that it was quite different to the MX7000 that I was looking at.  However, I didn’t know that he had done another workshop for the MX4000 and 7000.  That thread is proving to be extremely helpful on this project.  Martin did a great job – yet again.

 

I have now got to the stage where the power board is out and ready for working on.  The amount of dust inside the unit was huge – not really surprising after 13 years.  I have vacuumed everything so that I can now recognize the components and read the labels.  So far, I can’t see any horrendous burn marks but maybe the problem has been caught early.

 

Next step is to get the replacement caps and check the diodes.  Then I’ll put the parts in and re-solder the board for good measure.  That looks as if it could be a big job.

 

Thanks again for your help and advice.

 

Regards

 

Geoff

solderon29
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When you've removed the "dust of ages",and "the dog can see the rabbit",have a look at the scan coils connector on the base of the crt.You will almost certainly find that the last pin on the right hand end of the connector is burnt.Carefully loosen the little pcb that the connector goes to,and check for a burnt connection behind it.Resolder the connection,or if badly burnt,bypass the connector and solder the wire direct to the scan coil termination.

Nick

Step1
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Step1 replied on Sat, Jun 2 2012 3:04 PM

It must be stressed folks that CRT's should not be attempted by anyone who does not have a good understanding of the high voltages used in this set - quickly looking at Die bergers thread seems to suggest that the 27kv voltage is the dangerous bit and implies the 400 or so volts in the reservoir cap could be a cause of trouble - well IMO the smpsu cap is by far the bit to be cautious about. I have had a few belts from the EHT side before (not while powered but shortly after) and they hurt like hell, and can throw you off your chair - but I would not want to touch a fully charged reservoir capacitor in the power supply, IMO certain death or severe burns at the very least!!!!

 

ONLY TRAINED FOLKS SHOULD EVER SWITCH A TELLY ON WITH THE BACK REMOVED!

 

Please take care Geoff!

Olly

Evan
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Evan replied on Sun, Jun 3 2012 4:23 AM

If it were mine, I would fix it or have it fixed. There is no way I would part with such a beautiful TV. I hate modern TVs, absolutely characterless in terms of form bar BeoVison 5/9.

If I were ever to get back into watching TV in any capacity and could devise a way to get one of these sets to work over here I would have a white MX on its motorized floor or wall stand. Or for that matter, smack in the middle of the floor! No other way about it. 

Sorry to deviate from the course of this thread but I feel compelled to say this!

 

PS: Now here's a question for the pro's.. Were the MS versions sold stateside?

Beo4 'til I die!

geearr
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Thanks for all of the comments everyone, always appreciated.

 

Solderon29

 

I took some photos of the parts that I think that you were referring to.  The first was taken from the front where everything now looks clean and OK.  Can't seem to get that one to load up???

 

The second was taken at the back and there definitely looks like a bad joint at the back of the socket.  I can’t see anything on the fifth terminal but I will definitely have a go at re-soldering the second.  Just hope that it hasn’t burnt the contact pad away.

 

Well done and excellent advice – obviously the true voice of experience.

 

Olly

 

Safety advice is always welcome.  This is my first proper TV repair job – up till now, I have stuck to the radio, tape deck and turntable side of the business.  I’ve ripped open a few TVs to get some parts but I still have a lot to learn.  Normally, I leave the units off for a few days before diving in and every capacitor gets the screwdriver across the terminals.  So far, so good but one must never become over confident.

 

Evan

 

I agree that a tidy and clean MX is always a pleasure to look at.  Even though I now have two BV7s for general viewing duty, I cannot bring myself to throw the two MX7000s away.  They will be around for a while yet as long as they work.

 

Regards to all

 

Geoff


solderon29
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Yep,thats your problem.It's very burnt though,so I would bypass it as the plug/socket will be burnt too.Cut the wire where it goes into the plug,and resolder it direct the the terminal on the coil assembly.

Yes indeed,take care in there.The resevoir cap referred to is C9 on the main board,but it will discharge fairly quickly.

Check for dry jointed  C12 ,C102,103.Replace C100,C29 and C31,but otherwise "if it aint broke,don't fix it"

Super telly's,hope you can keep it going.

Nick

geearr
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geearr replied on Mon, Jun 4 2012 10:46 AM

Thanks again for all of your advice.

 

Excellent news for you all….. the MX7000 is now working again and the picture and sound are as good as they were before the failure.  This is my first ever TV repair and it was a very interesting experience for me.  Without the Beoworld team contribution, this TV would have been resting down at the dump. 

 

On the technical side, I cleaned up the pad around the pin and tested for damage.  I was surprised to find that there was plenty of conductive material around the pin so I decided to do a solder repair rather than by-pass the socket.  Not much room to work in but a fairly reasonable job in the end.  All of the resistance measurements through the coils looked good.

 

On the main board, I tested the diodes and made a mistake in measuring and concluding that D82 was open in both directions.  When I took the diode out it was OK so I put in a new 1N4002.  I replaced capacitor C100 at the same time.

 

I had bought a replacement IC for TR33, the BU2508DF, but when I compared measurements on the old one and the new one, they were basically the same.  So I left the old one in.

 

I repaired the solder joints that Nick referred to and then following his philosophy that if it is working – don’t change it, I decided to do no more.  I reasoned that the burning smell had come from the small arc at the pin and the melting plastic in the socket.  The picture had lost its horizontal deflection because the joint had finally broken and luckily I had caught it all before too much other damage had been caused.  So I decided to reassemble the TV set and test it.

 

First time switching on is always a concern for me but I bit the bullet and the TV fired up first time as if nothing had happened.  No more to report – it all looks good and I am still alive to tell the story.

 

Thanks again for all of your expertise.  This MX7000 has been raised from the dead at a total cost of $1 plus some more spares in my cabinet.

 

Best regards to you all

 

Geoff 

Step1
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Step1 replied on Mon, Jun 4 2012 6:59 PM

Well done Geoff :)

Olly

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