I now have an MX6000 which I need to repair. After 15 minutes or so, it shuts down (nicely, no noise nor smoke...). Haven't opened it yet, but apparently it needs new caps here and there and the supply protection circuit turns it off. I noticed there's a nice workshop on 3500/5500, does it apply to 6000 as well or does it have its own quirks?

The MX6000 is a higher integrated MX5500, the electronic is very similar to the older model. And they have the same problems.

 Replace the caps and it will work again. Dont forget the ones right in the middle of the mainboard. They usually have black feet ;)

I would tend to disagree about the level of integration ... whilst there may be a small reduction in components, generally the changes were the partitioning across the boards.

Again, unless one is qualified, I would hesitate to encourage amateurs to "have a go" ... opening can and indeed has been fatal.

I do not believe that beoworld should openly endorse this.  Lee, can you comment?

Neil

nobby:

Again, unless one is qualified, I would hesitate to encourage amateurs to "have a go" ... opening can and indeed has been fatal.

I do not believe that beoworld should openly endorse this.  Lee, can you comment?

Well, I've repaired several TVs (not B&O though, if I don't count the MX2000, which was a simple job) in the past and I'm still alive, so I presume I can manage this one too.

I agree though that these discussions always deserve a warning, as there may be people who don't realize the large voltages present in TV sets. Martin's workshop has clear warnings right in the beginning.

Short interim report. Per nobby's advice, I cleared the "last error" in service mode (was "pf") and waited till the set shut down again so I could confirm the current error. However, this time it did that hard, blowing the fuse. I now have the chassis apart, and TR1 (BUT12) has shorted. I'll replace that, and the caps that have been mentioned.

However, I also suspect the line output transistor and its cap (TR33 and C100). This transistor had been replaced by the shop the last time this set failed. It is now a BU2508DF, which includes a damper diode. The pictures in the MX5500 workshop show BU2508AF, without the diode. Can someone confirm which one it should be? The service manual on site sadly lacks section 3 with all the exact component values

Edit: the workshop actually shows BU508AF, while the MX6000 schematic just shows BU2508. The question remains, though  

BU2508DF is correct, also check solderings of C101/102 and the power supply area of the pcb since this could be the cause of the trouble.

ipaul:

BU2508DF is correct, also check solderings of C101/102 and the power supply area of the pcb since this could be the cause of the trouble.

Thanks - I already bought both AF and DF, they were cheap... the old transistor seemed OK but I'm replacing it anyway.

I'm working on the chassis now but have a delay, since most of the caps I've been pulling are of a higher voltage rating than what I have at hand... is it really necessary to have 35V caps filtering the 8-15 volts supply lines or would 25V do? Oh well, I'll need to go back to the store for some higher rating caps anyway, I'll just redo other solderings tonight...

OK, I got the caps and replaced every single electrolytic from 100uF up on the PS/deflection board (except for the two high voltage caps). I also replaced BU2508DF, BUT12 and went through any dubious looking solderings I could spot.

However, I still don't have the standby light and obviously the TV won't start. The fuse doesn't blow though, and BUT12 remains OK. What's next?

The "MX7000 won't come out of standby" topic seems like relevant reading and I'll think it over. I'm still open for suggestions, though, if anyone has quick ideas of what the dying BUT12 might have taken with itself to kill the standby supply...

Try checking the diodes on the secondairy part of the supply for short-circuit, especially the 2 doides mounted on the cooling plate (don't have the numbers at hand here).

Also check the drive transistors for the BUT12

nobby:

Also check the drive transistors for the BUT12

TR11 indeed seems to be shorted. Guess I'll just have to test just about everything

(once I come back from my long weekend in Iceland, that is )

Trace them back ... probably only 11, 10 and 9.

You lucky thing ... Iceland!

Neil

Well, this has been a good start for the week!

• I got back from the trip with just a bruised shoulder (shotgun cough) and a biblical hangover - the country is almost affordable at the current rates!
  
• after replacing TR11 (BC557) and some more resoldering, the MX sprung to life, and I've been watching it for two hours straight now!

Looks like 60 euros for a clean MX6000, motor stand and Beo4 wasn't such a bad deal after all

I will be returning on the general forum with some programming questions; the Beo4 and myself don't seem to get along too well. Thanks a lot to you all for your help! 

Aww, crap. The shutdown business is back again. 15 minutes from a cold start, and back to standby. Audio mode works fine however (the tv stays on for at least an hour), so I'd expect the problem to be at the line output stage?

I didn't replace any of the high voltage plastic caps nor the big diodes, all electrolytics are new however (except for the high voltage ones) and were spec'd at 105°C. Any ideas? 

Have you checked the selftest? There should be an error message stored in the cpu.

 Last error ....... ?

 

Last error = no

The set remains in standby after shutting down, so I suppose the CPU is running and would be able to store the error code if it was really shutting down due to power fail signal?

The last time the set shut down, I think I heard a not too loud "pop" sound maybe five seconds in advance. I think it's possible something might be actually arcing... I didn't find any tell-tales about that on the circuit boards the last time, though.

Hmmmm, listen to the high voltage transformer. It should be a very smooth humming sound.... summmmmmmmmmmmmmmm

If you hear something like summmm-tick-summmmmmmmmm-tick-tick-summmmmmmmm-tick....... the transformer has problems and needs replacement.

This is a very common problem. I've had already several damages on these transformers, almost every MX5000, 30-40% of the MX5500 need a new one, 10-20% of the MX6000 too.

Martin 

Hmmm ... never seen this failure mode on any of the MXs that I have ever seen ....

Well, in any case I tried to see & listen. There's a definite buzz at the tube neck area (I guess from the deflection coils) but other than that I don't hear anything funny.

However, since I opened the back cover and pulled the chassis half out to be able to see what's going on, the set has stayed on for an hour straight. I guess I'm back at the cracked / dry solder joint theory... 

Did you check the place I pointed to?

Not yet, I haven't had the energy to lift the set off the stand so I could pull the chassis completely out. Will do later and report on the results...

I resoldered a number of solder joints I didn't do last time (including one bad left by myself). The set has now worked fine for hours - even after I assembled it and the room is quite hot. Looks good