How to dismantle the MX5500:

 WARNING: in this tv are voltages up to 27KiloVolts, 27.000 Volt. If you hit the red cable or the picture tube while the tv is still under operation, then you will be injured or dead. This is really no fun! The power supply runs with around 350V and very high power, if you hit here the wrong part, there can be very high currents, melting metal, sparks and total loss of the equipment and your life.

Ok, but we are here to repair it, not to kill it  😜

Disconnect the mains plug, pull it out of the socket. Wait at least 1 hour, this will make the power supply not dangerous any more.

The high voltage of the picture tube can stay up to several days, so it is necessary to discharge them under control.

I would recomend to wait 1 day before you make repairs or opend the tv. 

All MX5500 and MX3500 have 4 bolts on the rear cover, if a LM-Sat is installed, there is a 5.th bolt in the middle of the cover. Open them, take care not to drop the cover, the picture tube could be damaged.

Ok, now you see the chassis in the MX. The chassis has on both sides a plastic guide, on the top is a small hook, press it an you can pull out the complette chassis to service position. But before you do this, there are a lot of wires fixed with some Omega shaped clamps on the rear side of the picture tube. Just twist them and make them loose.

Picture.....

On the rear side of the picture tube you see a steel cord, fixing the picture tube in the chassis. This steel cord is chassis ground = 0V

The first thing to remove is the red high voltage wire. This wire is the 27kV line... so take care not to touch the contact inside. It ends in a grey round rubber cover. If there is a lot of dust around this rubber cover, clean it first with a vacuum cleaner, please carefully, the picture tube is glass and can break. Dust can make problems with high voltage, there can be sparks otherwise, dust conducts high voltage.

Pull the rubber cover a little bit out on one side, now you see two metal hooks inside. Hold the rubber cover right in the middle, push it a little bit to the right and the left hook will dismount out of the hole inside the picture tube. Move a little bit left, and the right hook will disconnect now. Now you have the high voltage cable in your hand, dont touch the hole in the picture tube and dont touch the contact inside the rubber cover. There may be still some high voltage... press the contact to the steel cord and discharge it completely. There may be a small spark, after 1 day usually very small or nothing... but still good enough for a small electric shock.

OK, the most dangerous part is over now... 🙂

Now pull off the board on the neck of the picture tube. Do it carefully, dont bend the board or the glass. Put it in a clear plastic bag, it will be veeeeery dusty, black smoke and black fingers and black clothes... nasty. There is also a big wire for ground on this board, pull it off carefully, it is sometimes hard to remove, dont break the connector. When you assemble the tv later, dont forget this ground cable, otherwise there will be sparks around the neck of the picture tube !

Now pull the complete chassis almost out of the the plastic guides. Disconnect the wires for power from the power supply, the wire for demagnisation, the two speakers, the wire the ir control and the connector for the deflection.

Thats all, now pull out the board completely. All wires cannot be mistaken, there is only on position they fit to the board and all are different. The only wire that can be mixed, are the loudspeaker... ok, left to left and right to rigt connector, that's easy.

Picture.....  

 When you pull out the chassis, take care not to touch the power supply (look to the next part how it looks like...). On the power supply is a big golden capacitor, this cap is the main supply using around 350Volts. Usually this cap is discharged within some minutes, there should be no voltage at all after one day, but... dont touch it or the contacts on the board. if you want to be sure, measure it before you start working on it.

This is the complete chassis of this tv (yes Thomas, that's your LX5500 😐 ) 

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And from the rear:

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 On the left side is the power supply, on the right the tuner. In the middle, the U-shaped board the video and audio switch unit, above the crt tube board. Inside of all boards the RGB board and in the silver metal box the cpu board... and as a basic unit, the horizontal mainboard.

To disassemble the boards, start with this sequence:

- Open the left wing with the power supply, there are 2 hooks to open. Remove the wires from the power supply.

- Open the right wing with the tuner unit, remove the wires on the tuner board.

- Open the the H- frame in the middle, pull the U-shaped board a little bit backwards, ~10mm, not more!

- Remove the H-frame

- pull out vertical the RGB board around 15mm, just get it out of the small plastic rail on the mainboard... or the rails will break.

- now the U-shaped board can be opened 90 degrees and separated from the mainboard. More or less, all wires stay on the U-board...

- now mark all connectors with a pen on different locations, it makes assembly easier, maybe also some fotos...

- pull off all connectors/wires from the mainboard.

to be continued

The power supply:

The power supply can be set to a service position, press the hook on the top and a pull a second one on the black metal sheet in the front. The plastic is old and very hard. Watch out, these hooks can break easily. But the frames are still available, around 20 Euros each ;)

http://img178.imageshack.us/img178/5791/p1120009qe3.jpg

 Put it on the desk.... unhook the black cable

 http://img209.imageshack.us/img209/9238/p1120010pu4.jpg

 Disconnect these wires...

 http://img209.imageshack.us/img209/6999/p1120014li6.jpg

and here we are 😁 

Cleaned, washed....

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... and here all typical caps are replaced, almost like new 😁

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 The typical caps are replaced, the test in my (test-)MX5500 showed no problems. This power supply is working again within the specs.

Common Problems:

The MX is completely dead:

Check the fuse SI1. If this fuse is blown, there is a real severe defect on the power supply board. Usually there is a defect around tr1. Either TR1 is blown and has now a shourtcut. If this has happened, then check the blue C5 6.8nf 630-V for cold spots, better replace C5 and TR1. Sometimes the small transformer L5 has cold spots, sometimes there is a black hole around one pin.

 C5 and TR1 are located here:

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 The MX has a red light on top, but does not power up:

The MX wants to power up, you hear 3 times bzzz bzzz bzzz, the red Led is flashing 3 times, and nothing else happens, no picture, no sound.

The capacitors C20 and C25 are dead. Usually there are golden Roederstein used, 47uf 25V. If you find these types in your tv, replace them all. They have all problems. A better replacement for C20/C25 is 100uf or 220uf 25V.

The MX has during power up white lines on a grey screen:

This may be a defect, but it is a more common misbehaviour... let's say, most of the MX5500 have this. Almost quite normal, it's "design".

But defect caps can make this effect more visible and much longer.

The MX shuts down after some minutes or hours, the time between becomes shorter:

One or more caps are gone or out of spec.

Replace C20 + C25 100uf 25V, C11 + C15 1000uf 25V, C32 2200uf 16V, C18 470uf 16V, C10 470uf 63V..... and especially C5 MKP 6,8nf 630V (usually you hear a loud bang ! when it shuts down). Also replace TR1 .....

If the defect goes on, replace also C6 150uf 385V (also 220uf 400V possible) and C13 100uf 250V. C13 is hard to get, it has 4 Pins. If you replace it, make a wire bridge for the outer ring or a connection gets lost.

IMPORTANT:

Use only LOW ESR 105 degree caps for repacement. 85 degree types will cause serious trouble after some hours, their lifetime is gone after 3-4 month or earlier, the repair wont last very long! The power supply becomes very worm inside, temperatures of 50-70 degrees are quite normal.

Reason: 

A 85 degree cap can survive 85 degrees for around 1000 hours.

A 105 degree cap can survive 105 degrees for around 1000 hours.

Every 5-10 degrees less, the lifetime is doubled. So a good 105 degree type will last for around 2 exp 4 = 16 x longer than a 85 degree type. It makes a difference wether a tv runs 1000 hours or 16.000 hours 😜  

to be continued

The mainboard:

Rear view:

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Front view:

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The big black metal sheet is a frame and a cooler at the same time. From left to right you see 4 chips mounted on this frame:

2x TDA 2040 chips for the sound amplifier, a 11-pin Chip for the deflection and big transistor for the deflection.

Problems with the mainboard:

The MX is almost dead. The Red Light on the top is on, if you press TV the MX tries to power on, the Light turns to green for one second and then it powers off again 

 The reason could be a blown resistor R112, maybe combined with a defect diode D25. This is the 12V power supply for the tuner unit, the RGB and for the CPU. If there is a short, the resistor will burn. R112 = 0.1 Ohm 0.4 Watt. Check C67 on the teletext/cpu board, there must be 12V=

 The MX has serious trouble with the teletext. Missing or wrong text, wrong colours or does not power up

 The reason could be a blown resistor R109= 0.1 Ohm 0.4W, maybe combined with a defect diode D24. This is the power supply for the teletext module. Check also C66 on the teletext/cpu module. There must be 5V=.

The MX makes a sudden power off, very similar to a power fault in the power supply. The time between this defects becomes shorter, sometimes it's a loud "Bang" and the MX switches off

 The deflection transistor TR8 is bad and can have a shortcut. The reason is, that the cap in front of TR8 C12 is leaking and made an overload to the transistor, sometimes the transistor will not switch off and cause an overload to the power supply, blowing the fuse.

Sometimes there is a lot of dirt around this cap, sometimes a real puddle of dark electrolyt around the cap, the resistors around are green oxidated... in good condition it looks like the one on the picture, this one here is almost intact. Look at the top of the black cap, it's a little bit deformed. This means, the cap has pressure inside and the metal top was damaged.

Replace always both, TR8 BU508AF and the cap C12 220uF 16v

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The MX has sound on only one channel

 One of the TDA2040 cips has a dry joint to the board or may be defect. Replace this chip, it's cheap. The reason is, that the thermal expansion of the board and the metal cooler is not quite the same, ripping the chips out of the board. If one of the joints fails, the chips can go defect and overheat. The green and red caps around can be replaced, but usually they dont fail. But i had already one of the very big 3300uf caps in the background... it was really exploded. 😉 

When you replace the chips, mount the chips first with the clip and then start to solder. Dont forget the transparent insulation foil !

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The MX has trouble with colours, geometry, drop outs for some seconds

 This is a typical cap problem. If the power supply is ok, some of the caps on the mainboard will cause the same symptom. Replace more or less all caps on this board... they are all problem maker after 20 years.

 The MX has vertical stripes on the left, visible on dark surfaces like an echo, the stripes are a little bit brighter than the black background

Replace R36, 1K 1W, (next to L3)

Replace C18, 10nf 250V

Replace C16, 10nF 250V

 The MX makes strange sounds, buzzing, bzzzzzzschhhhh or the MX is working with a black picture, showing something like rainbow colours on the screen, dark blue and dark pink glowing

 The high voltage transformator has dry joints, resolder them carefully. The same can happen on the blue plastic caps, dry joints. There are also some big resistors on this board, becoming really hot. You can see the heat in fact, the board is deep brown around these hot parts. Clean the joints and resolder them carefully.

This defect is very dangerous, causing big black holes in the board. If this happened, it's very hard to repair because this caused overvoltage to many parts. At least, TR8 needs replacement.

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 Check all these blue caps that there is no bad joint. There are voltages between 180 to 600V on these parts, a defect joint can cause an ark and burn the board. That's a very bad damage... 

The MX is working perfect, you hear sound, you can switch channels,  everything is fine, but you have a complete black picture. The picture just faded out, becomes grey and disappears within 5 seconds. Sometimes it returns when you hit the MX

The heat line for the picture tube is defect... the tube itself is usually intact, no damage, but there is no heater current. This defect is caused by dry joints in this area, i had this already several times. Around these holes are tensions in the board, ripping some parts out of the board or even cracks, i cant explain why, probably heat. Some resistors and wire bridges are loose. Clean and resolder these parts carefully.

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Dry joints:

here you see one...

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The PAL/Secam/NTSC Decoder and RGBdriver board:

This is the RGB Board.

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 Typical defects: heat problems.

The picture is not clear, there are distortions or lines

Replace all electrolyt caps.

The picture flashes in green or red during power up, strong colour distortions, green or red lines

There seems to be a series of boards, where the copper lines are too thin and break. Check ground from 2pin connector to IC5 pin 6-7-8, IC4 pin 24, IC3 pin 8 and 22, IC7 pin 4. Sometimes the ground signal breaks.

Check also the 8V supply of IC7 pin 8, IC3 pin 9 and pin 18. This line also breaks invisible right under a smd part.

 Usually i replace the small 1uF caps by WIMA MKS-2-5 types. The tv picture becomes more sharp, the effect is visible.

The board can be tested easily outside the MX on your desk. Connect ground to the 2-pin "GROUND" connector, 16V to P37-2 or to the left side of R95. The power consumption is around 280mA at 16V, the chips become pretty worm.

Then check 12V on IC4 pin 6 and IC5 pin 1+2. Check 8V on IC7 pin 8.

Check powerfail signal on P37-5+6, use a 1k pullup resistor to 16V supply. When it pulls to ground, there is a power supply defect around TR19 and TR21.

The tuner board:

 OK, here we are, this is a tuner board of a MX5500. MX3500 and LX5500 use the same board, models with NICAM are almost the same... just the Nicam modul additional.

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 A very common problem is the black plastic frame, it breaks easily after this long time. But it is easy to remove just 4 bolts... and it should be removed, you will see why.

Common problems:

The MX is running perfect some time, then it shuts off suddenly or will not power up

No information is shown in service mode, maybe there is a power supply error shown (usually it does not). This defect can be the power supply or the mainboard, but also the tuner board.

There is a part of the power supply also on the tuner board, around TR9 and TR20.

All parts are here on the picture below...

You can also connect 8V and 12V to the tuner and test it separated from the MX on your desk. Use an external power regulated supply, for testing. If it does not take too long, you can use also 15V and a 47 Ohm resistor in line for the 8V. On your desk you dont have the risk of damaging the MX or yourself 😕

On connector P2 are, from left to right...

Pin 1+2 Powerfail line, Pin 3 15V, pin 4 ground, pin 5 8V

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Check L10, it looks like a big resistor. There must be on both sides around 15V. If not, the power supply or L6 on the mainboard has a problem. 

Check TR20 (BD436), it's the transistor with the black cooler, and D24 (1N4004). They become very hot and have heat problems. On the cathode (silver ring) of D24 must be 12V. I have had some defect D24's already.

Check TR9 (BC338), it also becomes hot, on it's emitter (signed E on the board) must be 5V

Check D25 (1N4148, next to D24...) on its cathode, there must be 13V

If one of these voltages are missing (and the power supply is already checked...), replace D24 (1N4004), D25-D28 (1N4148), TR20 (BD436), TR9 (BC338) and C78 (22uf).     

Check R158 (left in the corner...), there must be something around 5V. If it is less, then there is a powerfail in the MX 

For testing it on your desk connect Pin1 with a 1K resistor to 15V. If there is less than  5V on pin 1 then there is a Powerfail on the tuner board.

If you unsolder R158 and the MX powers up, then the defect is definitly on the tuner board. But beware... if it powers up and there is a bad shortcut on the board, you can kill the board by this short... But if the MX is still running and has sometimes the problem, that it switches off without any reason, then unsolder for testing R158. If the switch off problem disappears and changes to a different problem like bad colours, no tv station ... then the defect part is on the tuner board. But do not unsolder R158 for ever... the powerfail system would be disabled.

The tuner does not like some frequencies or does not find some tv stations

This can be a internal defect of the tuner unit, the silver box (ground...) is broken inside... usually you must open the box, that's a lot of work and check all connections of the small board to the box. Probably one is broken... very hard to find. I have heard of this defect, but never found on a MX5500, only on newer models.

But very common is this defect: the complete tuner box is broken out off the board... that's why you should look under the plastic frame ;)

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 Or the hf-jack is broken out of the box... and missing 😉

The tuner does not find any tv station in automatic search... but you see, that there are some stations. The tuner is running over them and does not stop. It is possible to tune manually to a certain station, but automatic does not work.

 The problem is R137, a trimmer, this one here. It has contact problems, dirt, dust, smoke. Make a colour point on it, turn it around several times and adjust it to the old position... or adjust it by tryout, it's not critical. The tuning process will stop if a tv station is found and the signal is strong enough. I would also replace the cap C102 (2.2uf) next to it.

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The MX has no sound, but you see a perfect picture.

Check IC2 TDA2557. 12V at pin 13+15, Ground on 14. If wrong, it's omething around TR9 and TR20... look above.

If it becomes hot, replace it.

The MX has a grey screen with white snow, does not find anything

 That's pretty difficult...

Check IC4 SAB3037. Usually it will show a error message ( "C0" = tuning citac ) on selftest. Check 12V on pin13, 13V on pin 19.

Start a tuning process, on pin 12 there must be an increasing or decreasing voltage beginning dependent on the frequency from 1V till 25V.Low frequency around 1V, high frequency around 25V. This is the tuning voltage for the tuner box.

If any tv stations are found, the pin 5 becomes 0V (the signal comes from IC1 Pin 8 (_STOP_TUNE_).

Depending on the frequency, the pins 15+16+17 switch between 0V-12V.

The MX has a darkgrey or black screen with tiny small white snow, does not find anything

 This is the tuner box... sorry, it needs replacement. But before exchanging check all voltages... maybe some are missing.

This defect is typical for overvoltage on the hf-jack. Usually the tunerbox is destroyed, the power supplies on the tuner board (D24-D28) and very common IC5 TDA8124, i found this several times. The overvoltage kills the 12V on the tuner board, more or less all chips will have trouble to survive...

The MX finds tv stations, stops and continiues tuning

Check R137, see above...

The MX finds tv stations, stops, but fine tuning is not good

Replace C32 (22uf), C31 (100uf), C35 (1uf), C36 (1uf), C37 (10uf).... it makes always sense to replace them ;)

The MX finds tv stations, but the picture is distorted, sync is bad, picture is running

Replace C30 (4,7uf), C2 (1uf) .... i replace all 1uf always against 1uf MKS-2-5 types, they are much better.

The picture is grey, white is grey, black is grey, distortions

Replace C5 (10uf), C97 (10uf)

to be continued

The video and audio switch board:

This is the U-board... it's the video and audio matrix. Every source can be controlled from every input to every output line. Inside this board are around a hundred electronic switches.

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Typical defects: dry joints.

Resolder the AV1 and AV2 sockets, usually you will find some cracks there.

There are 3 very hot resistors, you can see the heat, the board is deep brown around these resistors. Clean the contacts and resolder them and the parts around.

The 1uf caps can be replaced by WIMA MKS-2-5 types. Sound and picture become better, you can see and hear it.

On the top is C221 470uf 25V, replace it. Usually its very dirty and hot...

The picture tube board:

 This is the picture tube board. 

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 Typical defects: dry joints... and usually a lot of them. If one of the RGB drives is defect, then you see a complete colour missing, the picture is totally green or red.

This board becomes hot, very hot and very high voltage, so it collects all the dust in the air. This one here is pretty clean, i did not clean it for the photo... but after 20 years it's usually black and dusty.

Resolder the socket for the picture tube, the dry joints and replace the cap C6 4,7uf 25V. Clean the tube socket with alcohol or paint thinner very carefully. Any rest of the fluid used in the solder will cause sparks because of the high voltage.

Be very carefull with the grey box. It's just a high voltage trimmer... but very expensive and very hard to get. 70 Euro 😉

On the backside you see 2 trimmers: G2 and FOCUS. Focus is pretty clear what it does, right? Here you can adjust the the Focus of the picture tube. Use a long plastic tool and never metal for it... it's better for the MX and for your life.

G2 is something like brightness and contrast at the same time. Be carefull not to turn around without reason. The voltage on this trimmer can magnetize the picture tube, it becomes too bright and the picture can suddenly become blue or pink. This can damage the tube irreversible.

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 The IR Transceiver

A real funny defect happened now on one of my own MX5500. After 5-10 Minutes the MX switched off, no sound, no picture, also the red led was off and there was no function at all, complete dead from one second to the other.

After waiting around one minute suddenly the red led was there again, i could start the MX quite normal. Interesting is: there is no error message at all, nothing in service mode.

This happened several times, always just one time, never twice a day.

OK, everything on this MX was already done, new caps, new dst, everything clean and in very good condition. So i decided to control the 5V supply, since there was no error message at all, there must be something with the cpu. And i was right, there was a drop of the 5V supply when it happened.

Here is the solution: it's the IR board. There are 2 smd caps 220uF 10V. Defect. When the cpu sends an ir command, these caps have to buffer the 5V since the ir diodes need a lot of current.

2x C6 = 220uF 16V, standard caps will work.

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So, remove the finisher on the top of the MX, it's easy to disassemble when the rear cover is removed, 4 hooks.

Good luck!

Martin

New software for the MX5500:

The latest software for the MX3500/5500/LX5500 is 2.2S or 2.2P.

S= Standard or P= PIP Module.

 If you like an upgrade for "DVD", it's possible 😐

 link

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to be continued