Hi B&O friends,

last week a friend of mine came with a defect MX4000 and needed some help with this tv. The defects on this tv are 90% always the same, so i think, that a small workshop would help other users.

I dont recommend this to a totally beginner, but if you know how to handle a tv with 27kiloVolts voltage, ok, then go on. If not, stop here... i dont want that you terminate yourself and your MX tv...

The mainboard and some of the other boards are universal boards, the mainboard is used in any MX4000/6000/7000 and AV9000. The same applies to the RGB driver/decoder board and the tuner unit. The AV switch unit is also used in MX4000/6000 and 7000, the AV9000 uses a different AV switchboard.

Additional are minor differences in the teletext and sound amplifier boards.

The tv should be unplugged to mains one day before, the MX can store in its caps high voltages up to several hours, so make sure to wait one day.

Remove the rear cover. Usually its fixed with 4 bolts, if a satellite decoder is used, there is one additional bolt.

Then you see this...

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On the left and right side of the mainboard is a grey plastic guide, pull the small hook and you can pull the complete chassis out of the cabinet. Some of the wires have to be loosened out of some plastic hooks, looking like a omega. Twist them and pull the wires out. Pull the chassis complete into service position. Then press the black plastic hooks on the frames, there are 2 hooks on every side, one on the top, the other near the alumenum plate on the front. Take care not to break them, be very carefull, the plastic becomes really hard and can break easily.

Then the chassis should look like this. Like a butterfly...

  link

On the left side is the RGB/PAL decoder/driver. In the middle the U-shaped AV-switch (it contains the switch unit, the cpu, teletext decoder and the sound amplifier), on the right the tuner unit. The mainboard with the powersupply and the defection is the big horizontal board.

Now you should remove the red high voltage wire from the tube. It's here...

link

Inside the grey rubber plug is a steel hook. DO NOT PULL this plug if you dont know exactly what you are doing or you will break the glass of the tube! That means total loss of your MX!

OK, do it this way. Pull the rubber on the top a little bit outwards, now you can see a steel hook inside, shaped like a big T. Push the plug with the hook a little bit down, then one piece of the hook will unplug out of the glass, then move the plug a little bit up, then the second hook will unplug. Make sure not to touch the steel hook, there could be still high voltage!

On the backside of the tube is a steel cord, this is ground, connect this high voltage wire to the cord, unload any currents here.

 Unplug the black main power cord and the white degauss coil cord. They are here in this grey plastic cover.... just pull.

  link

 

 Then remove the wires from the picture tube board. There are 4 wires. Remove the black and the white wire, to unplug the red wire you have to press the small lock on the grey box... just a little bit and you can pull the wire out of the the box. Remove the ground wire on the underside... and do never forget this ground cable when you operate the MX or you will have a firework of sparks around the neck of the picture tube. Doesnt look good and dangerous to the electronic.

 Pull the tube board from the tube, do it straight or you damage the connectors. Check the joints of the big resistors and the three transistors, sometimes there are dry joints on this board... if one of the RGB colours is missing, you can be sure there is a bad joint on this board.

  link
 

 Unplug the two speaker wires, the black IR wires and the white keyboard wires, they are here. Mark the plug for the speakers or... left is left and right is right ;)

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 Unplug the deflection and power supply from the mainboard, they are here, the two white wires.

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Unplug the wires from the RGB and tuner board. Make a mark with a pencil on the sockets. Especially on the tuner board are some sockets that can be mixed up... ;)

Remove these boards from the mainboard, if they are in horizontal position (watch the two plastic straps, unhook them from the alumenum frame) the can be removed easily from the mainboard.

Pull the AV-swichboard outwards, about 45 degrees, on the top is a H-shaped black plastic frame, unhook it from the AV switchboard. Unplug the wires from the mainboard in the front of the mainboard, 5 left, 2 right.

Unhook the strap of the AV-switchboard from the alumenum frame. Move the AV-switchboard to a horizontal position and remove it.

 Now you can remove the mainboard out of the cabinet. And here we are, this is the mainboard.

link

 Remove the alumenum frame ( 3 bolts), remove the grey plastic frame ( 3 bolts).

Now it looks like this...

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Now you can heat up your solder iron....

Known defects on the mainboard:

1.) Most of the caps are ready for replacement. Especially C100 fails very often, sometimes there is a real puddle of acid around this cap. If C100 failed, TR33 will be dead, sometimes followed by D82. If this happened, only the red light is on, if you switch the MX on there is a BANG

2.) Dry joints, very common to C101, C102 and C103.

3.) Blown fuse F1: TR1=BUT12 is dead, also C12 6.8nF failed.

4.) Sparks around the high voltage transformer: bad joints to the blue caps or a blown transformer. Or maybe a forgotten ground cable to the tube board...

5.) Bad geometrie: bad caps around the geometrie controller IC4=TDA8172 or the controller itself. Sometimes bad joints to this chip.

6.) a very loud "Bang", then dead: C102 failed, TR33 dead

One of the most famous faults is a burned C102, a defect BU2508DF and a defect D82 and C100... they are all here ;)

link

 

Check all connectors to the blue plastic caps, they can become loose and if this happens, there is a nice firework on the board. Especially when C102 fails, there are severe damages to the board, holes and lots of high voltage to all parts. So if you heard something like "  SCHHHHHHHH    BANG BANG" check this cap. And dont wait, do it really fast ;)

OK, here is what you need:

Part list:

Replace all of these parts and you have probably eliminated around 90% of all faults:

C32, C130:                                  2x 1uF 50V (use a MKS-2-5 Wima instead...)

C61:                                            1x 2,2uF 50

C137:                                          1x 22uF 50V

C31:                                            1x 47uF 63V

C29, C132:                                  1x 100uF 40V

 C82:                                            2x 100uF 63V

C100:                                           1x 220uF 35V

C44, C120, C121, C131, C134:     5x 470uF 25V

C46:                                              1x 470uF 63V

C48, C53:                                      2x 1000uf 35V

C52:                                              1x 2200uF 16V

D82:                                              1x 1N4002

TR33:                                             1x BU2508DF (watch out for "DF", not "AF", and manufacturer Philips) The "AF" type can fail after some hours, a diode is missing in the AF type.

 Use "low ESR" caps, 105 degrees temperature types. Do not use cheap 85 degree types, they will fail within short time again.

 There are only 2 caps, that do usually not need replacement: C09 and C42, they are the big caps of the power supply. Usually they do not fail... and they are very, very hard to get and really expensive. 

 Additional measurements:

Check all diodes with your multimeter, in general there should be around 0.5 - 0.6V in flow direction. The diodes D34 and D36 (they are mounted next to TR33) have around 0.4V.  In opposite direction open, no flow.

If you have a special isolation 220V transformer, you can also measure some voltages on these caps during operation, but dont do this connected to the normal 220V mains:

C29: 5V

C31: -5V

C44: -8.5V in operation, -0,6V in standby

C48: 15-16V in operation, 0.8V in standby

C53: 8-9V in operation, 0.5V in standby

C52: 8-9V in operation and standby 

C9: 300V, take care, very dangerous...

C82: 150-190V, depends on the model...

C120: 13V in operation

C121: 7V in operation

 

 

Enter Service Mode:

To enter service mode you shortcircuit connector P700 on the AV-Switchboard, P700 is right above AV-Port 2. It's only necessary to connect a second.

Then you see the type, serialnumber and the last error of the unit

For example: 3313   10195331 Last error no

Press the right arrow on your BL1000... (here some examples of a MX6000)

Rdr 50 (Red drive)

Gdr 45 (Green drive)

Rcu 28 (Red cut off balance)

Gcu 29 (Green cut off balance)

BRI 03 (Brilliance Preset)

COL 03 (Color Preset)

Now for geometry:

Hfq 37 (Horizontal frequency)

Hph 35 (Horizontal phase)

Ham 22 (Horizontal amplitude)

Vam 29 (Vertical amplitude)

Vsc 32 (Vertical S-correction)

Vsh 30 (Vertical shift for centering)

Vli 18 ( Vertical linearity)

EWc 05 (EastWest corner)

EWp 15 (EW parabola)

EWt 41 (EW tilt)

WARNING: dont transfer these data to your tv without writing down the original data. These data are special for your tube, that means they are unique only for your tv. Just for this one. The reason why i write here the data of a MX6000 is, that you have a comparison to your data, they will probably not match. But the EEPROM can loose data and here are some ;)

 Last Error No:

No tells you the last error of your tv, it will be stored in the EEPROM... if the MX has still the time and the power to do it.

No = no error registered

PF =  Power Fail

00 till FF =  Error address on the I2C bus

DF = Data failure (maybe EEPROM 6IC6 on the cpu board defect)

4E = 1/38IC6 Tuner & IF port expander

84 = 1/38IC2 A2 Stereo decoder

40 = 31IC7 NICAM stereo decoder

42 = 41IC5 D/A converter for cut-off and drive

22 = 37IC2 Teletext decoder

8C = 13IC2 Deflection controller

82 = 14IC1 Audio Controller

86 = 14IC9 Video Controller (14IC9 means Board 14 Chip IC9)

 

 

 

Good luck!

Martin