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MX7000 CRT - No Power

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flex
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flex posted on Fri, Nov 23 2018 1:55 PM

Hi Guys,

I am new here!

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 did find an old thread called Workshop How to rebuild a MX4000 MX6000 MX7000 and AV9000 but it is missing the pictures.

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

I am fully aware of the high voltage dangers of working on CRT's so am hoping this might be an easyish fix. I have experience with soldering / electronics etc. and I have done a lot of research on how to discharge this particular CRT and plan to get a tool like is used in this video to do so.

https://www.youtube.com/watch?v=rhMT40hDNFw

I am hoping to bring this beauty back to life for use in a retro gaming setup.

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flex
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flex replied on Thu, Jan 10 2019 11:33 PM

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 Crying

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.

 

I am sending out a cry for help for anyone who has experience with these models that might be able to help me!

 

dabbler
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Did you ever fix this problem?

 

I have a mx4000 with the same problem, it switches into standyby after a few minutes, so far ive replaced : c61, c137, c31, c29, c132, c82, c100, c44, c120, c121, c131, c134, c46. c48, c53, c53, d82 & tr33 and the TV still has the same issue, does anyone have any thoughts please?

 

flex
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flex replied on Sun, Jul 28 2019 10:49 AM

Not with this particular set in the end I threw in the towel because I believed there was an issue with the high voltage transformer and ultimately I could not find a suitable replacement part, also this particular set had been run for many many hours as was evident from burn in on the tube etc. I ended up finding another MX7000 for a really good price in much better condition, I still kept some bits back from the old set though as spares.

I learnt a fair bit about these sets on my journey though and they have a very complex / clever protection system that kicks in if something is amiss hence the set staying in standby mode with the red led. The trick is to find out which circuit is kicking the protection mode in, with my old set i knew it was to do with the high voltage deflection circuit so was concentrating on the main board where these components are but it could be anywhere, it is possible to force the TV to come on and bypass this protection circuit by shorting the service mode pins and turning it on so you can read the last error code from the service menu but this has its own associated risks as it can damage the set / components running like this and is quite risky.

There is good information on the protection circuits in the service manual especially if you follow the wiring diagrams.

You mentioned you have replaced most of the caps but have you verified there are no dry solder joints as this is a really common problem which can cause this and I certainly found a few.

Have you followed all the advice given on the workshop thread i linked in my original post?

Also I posted this issue over in the workbench section of this forum instead of the general section and had a much better response there so suggest you do the same for your issue. Here is the link as it has some better information about my issue:

https://forum.beoworld.org/forums/t/35992.aspx

Also the following thread provides an example about how to read what is going on with the protection circuit. This is pretty advanced stuff though and was above my capabilities personally but it may help you out.

https://archivedforum.beoworld.org/forums/t/26870.aspx

Hope any of that helps. Good Luck!

P.S. Please remember to be extremely careful when working on the high voltage circuits especially if bypassing any protection circuit. Like someone said to me get a professional to look if not sure   

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