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MX4000 Repair

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dabbler
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dabbler posted on Sat, Jul 27 2019 8:29 PM

Hi, I hope some one can advise me on a repair im trying to complete. I picked up a MX4000 and it has the following issue:

Switch it on, after a couple of minutes it goes into standby, the standby led is on. You switch it back on and after a minute it will go back into standby, this repeats and the time to go into standby from on decreases.

I took it apart thinking maybe a powersupply issue, someone in the past has already reflowed nearly all the PSU board components (hmmmm) any way, i reflowed again - no difference and the problem persists.

Ive now replaced: c32, c130, c61, c137, c31, c29, c132, c82, c100. c44. c120. c121, c131, c134, c46, c48, c53, c52, d82 and tr33

The problem still exists, does any one have any thoughts please? 

Many thanks for your help.

Darren

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dabbler
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Some good news. The MX4000 is now fully functional! Thanks to all that posted here (and via email) for help and guidance,

FYI, the error is B6 and i never did find out what that error was.

I finally repaired the switching off issue, by re-capping board 13. I ended up thinking, id just re-cap every board and then check transistors, diodes, however after i recapped the U shaped board (which fixed the onscreen menu colour bleed) I run out of many capacitors, i had just enough to complete board 13 - so i used them up!

I reassembled the set to keep it safe and out of people way, thought i power it up and hey presto - fully working!

I hope this helps others, it really is a lovely CRT. Ive learnt - capacitors (even if they dont look bad or bulging) can fix a whole variety of issues, and on old 80's / 90's kit - just replace them, it doesn't take long and will need to be done at some point any way!

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dabbler
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Ive noticed another issue that i didn't notice before regarding the on screen menus, they appear to be bleeding and have colours missing (i didn't know it wasn't supposed to look like this - its my first B&O set!) - this is the onscreen menu only, the teletext display is 100% perfect.

Click for larger image:

Ive enabled the service menu, and its very hard to read the code due to this problem, turning the contrast / brightness up im just able to make out the last error code, which looks like B6 or maybe 86, which is :

14IC9 Video Controller (14IC9 means Board 14 Chip IC9)
Im determined to fix this set, its in such lovely cosmetic condition with remote and motorised stand.
I reached out to a couple of forum members via email, but am hoping other out there will also be able to point me in the right direction.

 

dabbler
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14IC9 Video Controller (14IC9 means Board 14 Chip IC9), this is a TEA6416 by ST.

It is a video matrix ic.

Should i replace the chip, or does the B&O error codes suggest this has an issue due to other factors, caps etc?

Im not sure how to proceed so any help would be great,

 

Thankyou

flex
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flex replied on Tue, Jul 30 2019 10:47 PM

Looks like the lack of colour is probably a symptom of the issue on the video board.

What you have to remember about the error code is it is not pin pointing the exact place of the issue but pointing at the circuit and chip that is telling the protection mode to kick in and keep the TV in standby mode. 

Your issue (86 = 14IC9 Video Controller) is not specifically going to be IC9 that is the issue but one of the many components it is monitoring / connected to. I really am no expert here but I wouldn't mind betting your issue is on PCB 14 though as this is where most of the video signal circuitry is and we can see from your screenshot that you maybe have an issue here with the red colour as that is the colour of the text that is missing / very faint and seems to be what is bleeding in.

Go through Diagram D & E for the audio / video switching circuit in the service manual with a fine tooth comb and check all of the components on PCB 14, looking for dry joints / faulty components and probably a recap. PCB 14 should be that U shaped board directly at the back of the set with the scart sockets on and the service mode pins etc.

Let me know how you get on.

Good Luck!

dabbler
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dabbler replied on Wed, Jul 31 2019 10:59 AM

Thanks for the reply! I have PCB14 out now, it looks ok - still im going to re-cap it, reflow anything suspect and see if that makes a difference. Fingers crossed!

dabbler
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Well I recapped board 14 and now the onscreen menu is sharp and correct - great.

Alas it still switched itself off :-(

One problem fixed. Main one still outstanding.

At least I can read the code's now :

 

dabbler
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I cant find any reference to B6 at all. Any ideas please?

dabbler
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As a test, i killed the power to the set. Error code was "Last error no", it then switched itself off. I powered it back on and re-entered the service menu, the last error code is again B6. I wish i knew what this meant!!!

Also to note, when it switched itself off, it makes a slight "pop" like a static discharge of sorts (from the speakers), when i switch it off manually it doesn't do this..

flex
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flex replied on Fri, Aug 2 2019 2:29 PM

Progress!

B6 doesn't seem to be a common one that's for sure as not listed in any of the guides or the service manual. Have a good read of the service manual section 7-1 onward it might give some clues about how to troubleshoot these codes.

Hopefully someone here may have seen this before and can advise.

 

dabbler
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Some good news. The MX4000 is now fully functional! Thanks to all that posted here (and via email) for help and guidance,

FYI, the error is B6 and i never did find out what that error was.

I finally repaired the switching off issue, by re-capping board 13. I ended up thinking, id just re-cap every board and then check transistors, diodes, however after i recapped the U shaped board (which fixed the onscreen menu colour bleed) I run out of many capacitors, i had just enough to complete board 13 - so i used them up!

I reassembled the set to keep it safe and out of people way, thought i power it up and hey presto - fully working!

I hope this helps others, it really is a lovely CRT. Ive learnt - capacitors (even if they dont look bad or bulging) can fix a whole variety of issues, and on old 80's / 90's kit - just replace them, it doesn't take long and will need to be done at some point any way!

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