Hi all,

My MX4000 is having the problem that it only focuses properly in the centre of the picture. It is getting more and more out of focus when you get to the edges of the screen. 

Because it had a staying-in-stand-by problem I already replaced almost any electrolyt capacitor on the main board except the small 1uF/50V (C130 and C32) and 2u2/50V (C61) and the bigger 470uF/63V (C46) of the fly-back converter. When I turned it on for the first time after this refurbishing, the stand-by problem was over, but the picture wasn't focused at all. When I touched the focus potmeter it 'sprung' to focus, but not for the fully 100%; subtitles cannot be read. It also seems that turning the focus potmeter on the RGB board has no effect. Could the 4u7 C6 capacitor be the problem or is the focus potmeter bad?

Symmetry of the picture is OK and the picture is very stable.

Can anybody please help? 

Kind regards,

Bart.

Is there focus potiometer on the LOPT? Had this problem with computer monitors and its worked every time. Just remeber to turn it slowly.

Craig

Thanks Graig,

That could be a good hint; I did not pay attention on turning it slowly. I wll try it immediately.

BTW, what does "LOPT" stand for?

Regards, Bart.

Line output transformer I think. Just take care as this produces several thousand volts. When I have done this before I have found it easier to get someone else to watch the screen as you adjust it.

Craig

Yes, it reacts when I turn it slowly, but still I can't get it in focus: The picture is getting better and then...I am at the end of the potentiometer's reach.

There is no separate potmeter on the output transformer itself; the potmeter placed directly after (electronically) the transfomer on a different PCB placed on the neck of the tube.

After reading some topics on the forum I decided to try to turn G2 on the RGB board gently. This had a big positive effect on the picture. I can now read the text. Still, the picture is out of focus on the edges. It has 'shadows', like the colours are not laid exactly on top of each other.

What to do next? 

thanks in advance,

Bart.

It looks like the G2/focus unit is bad. 

Does anybody know where to buy a new one?

Regards Bart

Until recently, these were still stocked by your local dealer for about £25.

Failing that, grab one of another set.

Neil

Thanks,

Are they all the same; MX3500/MX5000 and MX4000/MX6000/MX7000?

Regards, Bart.

Yes. Original all the same.

Newer parts have a different design, but still the same function.

Thanks Die_Bogener!

My TV set has a white G2/focus unit, but there are also grey ones applied in MX sets that were made by Philips. So I assume these G2/focus potmeters can also be found in Philips TV sets? Maybe I can can get one from an old Philips TV. We do have a lot of Philips TV sets here in Holland ; much more than B&O. 

Do all these potmeters have the same value? 

Kind regards, Bart

Are the PCB's with the focus and G2 between a MX3500 and a MX4000 exchangable? The PCB of the MX3500 has different transistors; TFK43. The MX4000 has BF421. 

The boards are different, i dont know wether 3500 and 4000 are exchangeable... never tried.

But the focus/G2 unit is identical.

A B&O service centre made out that the boards of a 3500 and 4000 cannot be exchanged, that's a pity. 

It's a good thing that the G2/focus unit is nevertheless the same, but I don't dare to desolder the working one. If I break that one too, I have two TV sets to find a new G2/focus unit for. 

So that leaves me searching for a new/other G2/focus unit. I have already found out that that is very hard to find in Holland. I have phoned, mailed and visit a lot of potential suppliers, but to no avail. So far, a new one is not available and the used ones have been thrown away.

But in the end.......i will find one!

Regards, Bart.

I got one! And it solved the problem......for 98%. Now I have a minor problem with the Auto contrast. As soon as it catches light, the picture gets shadows on the edges of the screen. I know there are some problems with the auto contrast: A friend of mine had a MX3500 that switched off as soon as the sensor catched light. 

Does anybody know what the solution is?

Otherwise I replace the sensor with a fixed resistor.

PROBLEM SOLVED: I re-adjusted the G2 and focus with brilliance and focus at maximum and now it is perfect.

Thanks to all.

Regards Bart.