I have a Beovision MX6000 currently on the bench.
I normally don't do TV's or VCR's so my experience in these
matters is quite limited.
This particular white design MX6000 is in mint condition and one I
really would like to get going though as the plan is to put it into daily use.

Problem is that it won't start properly;
Mains on brings the standby LED on. So far so good.
Pressing TV on the Beolink 1000 turns off the standby LED and I can hear
the crisp sound of the highvoltage static charge as I would normally expect.
After apprx 2-3 seconds, I get a fairly loud pop from the speaker and the
MX6000 returns to standby.

As already said, I don't have a lot of experience to pour from regarding TV's but
from an electronic point of view, I could think of several reasons for this
behavior and probably spend hours tracing this fault.
However, I wouldn't be surprised if this is yet another standard fault
for this model and I'm sure that one of you experienced guys can give
me a hint or two where to look in the given case.

Martin

Start by checking if it will start in audio mode ok ... i.e. use the AV Radio ... if it starts ok, chances are its something in the HT section.

Neil

Neil,

What do you need as an input to try out the audio mode?

Brian

Thanks, Neil.
I see where you are going but I don't have a Beo4, can I use a Beolink 1000 ?

Martin

Dillen:

I see where you are going but I don't have a Beo4, can I use a Beolink 1000 ?

Sure, just use AV + RADIO (or something else). I don't think you even need a real input to see what happens, but you can connect a suitable Beomaster to the AV AUX link if you wish.

If this is a power supply / line output problem, my MX6000 case from last year might be helpful. It's still working great!

Thanks guys. Tournedos' MX6000 case thread and Die_Bogeners wonderful MX workshop thread
are both superb sources of information.

I measured around a bit and found a B-E short on TR33.
C100 and D82 both seems fine though I will of course replace C100 while in there.
I suppose a C-E short would potentially have damaged the HV transformer but
a B-E short maybe wouldn't ?

Any other things I can check ?

Martin

Dillen:

I measured around a bit and found a B-E short on TR33.

Are you sure it's shorted? It has a damper diode built-in between B-E, so it will look like it's conducting also in the "wrong way" on diode test range (of course it could be defect, I replaced mine just to be sure - it's just a couple of euros).

One test that did not end on the public forum in my case was to look at the underside of the chassis in dark and maybe tap around a little to find places that might be arcing over (bad solders most probably).

Yep, 25 ohms DC resistance both ways between B-E so definitely dead.
I just wonder why. When B-E shorts occur there's usually a good reason but of course the reason here could
be the transistor itself.

The built-in damper diode sits between C-E if I'm not mistaken. I'm aware of it, thanks.

Martin

Oh yeah, it wasn't the damper diode - I remembered incorrectly - but the resistor built in between B-E. Mine measured 33 ohms when new, which is actually the typical value given on the Philips datasheet for BU2508DF

Martin, if TR33 is the HT transistor and with the startup you do get the HT (for a short while) that transistor will likely be ok.

(i'm at work, don't have the diagram here..).

The short is because of a transformer driving the b-e of the HT transistor.

Check for bad solderings on C101/102/103 close to the HT transistor, also check for bad connection/solderings on the tube, deflectioncoil-connections and check for bad solderings (sometimes a magnifying glass comes in handy here !) at the doides in the power supply part and the coils/transofrmers in the deflection area.

There's a chance of 95% it's one of those....:)

Thanks also to you, Paul.

Yes, I checked the datasheet for the transistor and I was aware of the diode but
not the resistor.
I tested the transistor out of circuit and was fooled into believing it was dead, but it's not.
Obviously a very low impedance B-E path is needed.

I couldn't find any obvious faults, the C101/102/103 etc. all tested fine, I checked around and corrected
a couple of dodgy looking solders at the main board around the HV and power supply areas. I can't say that
I found anything specific but I now have a picture. So far so good.

It's not particularly dirty or dusty inside but I will give the whole inside a good clean and then a soak test.

Thanks for all the help, I will get back if it goes bad again.

Martin

Well...
It was dusted off using compressed air and worked fine yesterday but not today.
However, the symptoms are slightly different now;

- Mains on.
- Standby LED comes on.
- Pressing TV on the remote leads to a brief change from red to green LED and then back to red.
- The above can be repeated without removing mains.
- Occasionally a little audible thumb sound from the speaker as the red/green changes.

Am I looking for more cracked solders ?
C100/101/102/103 all measures fine but will be replaced none-the-less.

Any ideas ?

Martin

Again, look at the deflection panel solder side in the dark and try and start the tv ...

Thanks nobby,

I will replace the caps first and then do just that.

Martin

Just to clarify: we're talking about the little connection board on the tube neck: 5 coloured leads (black, yellow, orange, red, brown) are connected with a connector on a small pcb on the tube neck.

Take the connector out and check for burn marks (sometimes it even melts together with the other side !!) and flip over the connection board on the tube neck by slightly pushing out the 2 plastic clamps on the sides, so you can see the back of this little pcb.

Also looking at the back of the main pcb in the dark while starting the tv sometimes helps, you might see sparks where there is a bad soldering.

(i think this is what Neill is referring to).

If the C 101/102/103 didn't have bad solderings i wouldn't bother replacing them...

Thanks both of you.
I will check both the large mainboard and the little deflection board
under the tube neck.

Martin

OK, checked the boards, put in new capacitors and powered up again.
I didn't see any cracked solders but resoldered the deflection board anyways to be
on the safe side. The same goes for the main board, all connectors and larger
components were resoldered. As were anything else that looked the slightest bit
marginal.

First time it worked for 10 minutes then went into standby.
The first 5 minutes I was sitting in the dark, waiting for an eventual spark
(that didn't show) and so I was watching the screen as it went into standby.
Right after this, I powered up again and it ran for nearly half an hour
with me sitting in the dark watching the solderside of the mainboard.
I didn't notice any sparks or anything else as it went into standby again.

Picture and sound were both good while it worked.
Teletext also clear with bright white where supposed to be.

I suppose it could be a defect inside the HV transformer ?
Or is there something I'm missing ?

Martin

Dillen:

Right after this, I powered up again and it ran for nearly half an hour
with me sitting in the dark watching the solderside of the mainboard.

martin,

pardon the misspelled pun, but your DILLigENce never ceases to amaze me...

i hope you at least had a beer or two while sitting in the dark!

hope you get it running!

Oh Jeff, that was a nice one. 
Thanks.

I tend to become pretty stubborn with things like this and as much as I think
general repairs are fun, I really enjoy the occasional odd.
Tv's less so, though but I really still wanted to get this MX going again.

And this time my patience paid off - I saw the spark !
What a nice firework !

The TV started to power down after shorter and shorter time, finally only running
for a few seconds, the main board being very sensible to the touch and
I was able to locate a cracked solder at a blue 6n8 capacitor in the power
supply area. Even in a strong light I wasn't able to see the crack but under
a microscope, there it was. Very nice and very bad. The soldering at the
other pin of the same capacitor showed signs of stress under the microscope so
both ends were soldered properly.

Its running as I write this and I am quite confident this cured the poor thing.
Enough for today, it will be tested further tomorrow.

Thanks all for your help and suggestions. Greatly appreciated !

Martin

Hej

Martin

Du skal huske at skifte den blå tilbageløbs kondensator,den har garanteret

taget skade ellers er jeg bange for problemet genopstår

mvh

jan

Good...it's fun isn't it :), but that's why i made the remark abt having a magnifying glass at hand: i've been 'fooled' by these tv's many times already and rarely anything else brakes down but the solderings.

So if you want to play it safe just tap all boards with the tv on and see if the screen doesn't respond to the tapping and /or even better: check the boards with a magnifying glass.

On the smaller left and right pcb's are also some IC's regularly getting bad solderings, enough weak spots in these tv's as far as that is concerned but once dealth with that they hardly ever go wrong...