Mitsubishi VS-5072 (V-13 Chassis?)

[jaluhn]

Hello, I am in need of some advise from those with more knowedge than I.

I recently aquired an older mitsubishi projection TV, model VS-5072. The unit was given to me due to a power on problem, it was apparently working properly, was turned off then turned back shortly after and did not have any picture. The sound worked, and it was possible to change audio channels. I looked at it, checked all the fuses and did some basic testing. I observed that it apeared to power up normally, and the HV to the crt's seems to be working, since the distinct high voltage hum that would be expected is heard The audio system works completly with channel and volume controls working.

Upon visual inspection, I found evidence that a tranistor of the main power baord (IC9A1) had gotten quite hot (scorced pcb in the area) and the solder on one lead was either broken free of very weak. (I gently touched the top in trying to identify it and when I did this it broke free of the pcb, with 2 traces having come loose from the board and the one broken at the solder joint. I suspect the solder joint failed eariler) This IC appeared to be a 'SE130N' which I was able to replace with a new component. With the new ic installed, I now observe a series of clicking noises coming from somewhere on the main power board when the unit is turned on, with the audio and HV systems still working as previously observed. Also, when first plugged in (tv turned off) several clicks are heard in the same area with decreasing frequancy. These sound similar to those heard when the unit is turned on, though there are only 4-5 of them. Sounds like something is charging up, though I am not sure what would be clicking.

This problem sounds very similar to a dersiption I have found of a common problem in the VZ-2 chassis. But, from what I can tell, this unit is a 'V-13' chassis. Is this chassis similar? I have not yet gone through and check for shorted caps, this would be my next step. What I would like to know, however, is if I should look for any other components. I have found refernce to a repair kit for the VZ-2 chassis which includes several caps and resistors, will this work for my unit?
Thanks ~ John

[Krankshaft]

Re: Mitsubishi VS-5072 (V-13 Chassis?)

Check the necks of the picture tubes while the set is on are the heaters glowing?

The reason the set is shutting down is because the power supply is entering protection mode due to a fault.

The blown semiconductor you replaced (an error amp IC) most likely has other shorted components around it and thats why the set is shutting off now.

Your problem probably is in the power supplies feedback circuit. The voltage from the supply is rising past its normal limits and the protection circuits are shutting the set down.

[Maxxarcade]

Re: Mitsubishi VS-5072 (V-13 Chassis?)

These TV's usually have tons of leaking caps in them too. Look for black goo coming out of the bottom, and they will smell if the leads are heated with a soldering iron. The smaller size ones between 1uf and 220uf are the most commonly bad ones.

Also resolder any broken solder joints. Sounds like it has a few of those

[jaluhn]

Re: Mitsubishi VS-5072 (V-13 Chassis?)

I see no evidence of the tube heaters working, though I am not exactly sure what I'm looking for. There are no visably glowing parts within the viable part of the tube neck. I presume I should be able to see it glowing brightly if it was working, correct?

I looked at the caps I could see and didn't see any witch looked to be leaking. I also checked most of the caps on the main board for shorts with a DMM and didn't find any.

When the unit is plugged in (not turned on) I can heard a 'tick tick tick' sound coming from somewhere on the main pcb, about once per second, and goes away after about 10 seconds with a decreased frequancy at the end. Sounds like something charging up and discharging. Also, if the power supply board is plugged into the wall (not turned on) and then the wire to the main pcb (3 wire, solid red, green & brown wires, connector 'PB' on the PS board and 'DB' on the Main pcb) is connected, a substantial spark is observed on the brown wire. Seems like something is discharging through that wire, doesn't seem normal to me. No ticking sound is heard at any time if this is done. When the unit is turned on, a faster clicking noise (~5 hz) is heard from the same area of the board, but the sound is different. This sound more like the power supply rappidly cycling. When the power is turned off, the same tick tick noise is heard for about 5 seconds, ending in a brief sizzle type sound. It sounds alot to me like something is shorted out on the main board, but I haven;t had much luck finding it. Any ideas?

I didn't see any other cracked solder joints, but haven't looked too hard yet. I think the tick sound I'm hearing is definetly abnormal and would like to find out what's going on there first.

Anyone know of a source for a schematic / service manual for this unit? If someone could scan a schematic I would really appreciate it, athough just a source where I could get one would help too.

Also, how similar is this unit to a VZ-2 chassis? I've found alot of refernce to power problems for the VZ-2, and MCM has a power kit to fix that unit, but I don't know if it will work on mine. Will it?
Thanks ~ John

[Krankshaft]

Re: Mitsubishi VS-5072 (V-13 Chassis?)

Yes you should observe an orange glow from the clear neck of all three tubes.

I would investigate the source of the popping noise I have a feeling that your flyback is arcing the flyback also supplies power to the tube heaters.

It is also responsible for supplying high voltage to the tube anodes to accelerate the electrons generated by the cathode to strike the phosphor surface of the tube hard enough to emit light.

In other words without the tube heaters no electrons will be generated and without the High Voltage at the anode the electrons won't hit the phosphors hard enough to emit light so in any case you won't have any picture.

I would listen closer around the flyback.

Also check the horizontal output transistor although the chassis shouldn't power up at all if it was fried check it anyways.

Here is a link to a service manual for your set but its not free:

http://www.servicemanuals.net/result...9&model=VS5072

[tvtech]

Re: Mitsubishi VS-5072 (V-13 Chassis?)

Be sure to check for leakage of the crt coolant,I usually avoided these sets due to this problem,If the crts are leaking you will see corrosion on the chassis and then the set is not worth repair as the coolant eats the traces.I will post a few repair tips from a repair database I have access to.As for the capacitor problem,what year was your set manufactured?It is printed on the same sticker as the model number and serial number if your set was made before 1995 expect to have a good number of leakers and you can't always tell by checking them with a dmm you have to use a cap analyzer or simply remove each capacitor and look for leakage on the pcb and the bung of the capacitor.

[Krankshaft]

Re: Mitsubishi VS-5072 (V-13 Chassis?)

TV tech makes a good point check for coolant leakage around the bells of the tubes.

The clear coolant container is located between the lens and the tube face.

So if it decided to leak it would drip down the tubes back and continue from there.

It is actually ethylene glycol similar to car antifreeze however its clear so as to not affect color reproduction.

If its leaking it could have allowed the HV to arc from the anode cap or it could have eaten away at the CRT neck boards and everything else in its path.

I'm not sure what the aquadag is made of other then graphite and some kind of binder but the coolant may be able to eat that off the tube bells as well.

From my experience the blue likes to leak first then the green with the red rarely ever needing replacement.

The coolant usually leaks because the gaskets give way a simple problem if caught early a disaster if caught too late.